Placental growth factor blunts uterine artery responses to angiotensin II

OBJECTIVE

Changes in maternal serum concentration of placental growth factor (PlGF) and vascular response to intravascular infusion of Angiotensin II (Ang II) follow a bell-shaped curve pattern during gestation. This study evaluates the effects of PlGF and soluble vascular endothelial growth factor receptor-1 (sFlt-1) on responses of human uterine arteries (UA) to Ang II.

DESIGN

Experimental.

SETTING

Baylor College of Medicine and Texas Children's Hospital-Pavilion for Women.

SAMPLE

Uterine arteries samples (n = 14) were obtained from normotensive women undergoing caesarean hysterectomy at ≥32 weeks.

METHODS

Uterine arteries rings were incubated with (1) Krebs solution; (2) PlGF at 1.45, 14.5, and 500 pg/ml; (3) sFlt-1 at 2 ng/ml; and (4) a combination of sFlt-1, and PlGF. Dose-contraction responses to Ang II were determined in UA rings incubated in the above-mentioned conditions. Responses were also measured in presence of L-NAME or inhibitors of endothelium-derived hyperpolarising factor: apamine and charybdotoxin. The t-test was used for comparisons.

MAIN OUTCOME MEASURE

Changes in vascular reactivity of UA rings.

RESULTS

PlGF blunted (P = 0.03) and sFlt-1 increased (P <0.01) the UA maximum responses to Ang II. A combination of sFlt-1 and PlGF blunted UA responses to Ang II (P < 0.05). l-NAME, apamine, and charybdotoxin reversed the relaxation effects of PlGF on UA responses to Ang II (P < 0.05).

CONCLUSIONS

PlGF contributes to the blunted vascular response to Angiotensin II during normotensive pregnancies and sFlt-1 appears to attenuate this effect. PlGF and sFlt-1 may contribute to the regulation of vascular tone during pregnancy by altering the vascular response to Angiotensin II.

FUNDING

Baylor College of Medicine.

TWEETABLE ABSTRACT

Placental growth factor and soluble vascular endothelial growth factor receptor-1 modulate the uterine artery response to Angiotensin II in normotensive pregnant women.

Spontaneous abortion is associated with elevated systemic C5a and reduced mRNA of complement inhibitory proteins in placenta

Spontaneous abortion in early pregnancy due to unknown reasons is a common problem. The excess complement activation and consequent placental inflammation and anti-angiogenic milieu is emerging as an important associated factor in many pregnancy-related complications. In the present study we sought to examine the expression of complement inhibitory proteins at the feto-maternal interface and levels of complement split products in the circulation to understand their role in spontaneous abortion. Consenting pregnant women who either underwent elective abortion due to non-clinical reasons (n = 13) or suffered miscarriage (n = 14) were recruited for the study. Systemic levels of complement factors C3a and C5a were measured by enzyme-linked immunosorbent assay (ELISA). Plasma C5 and C3 protein levels were examined by Western blot. Expressions of complement regulatory proteins such as CD46 and CD55 in the decidua were investigated by quantitative polymerase chain reaction (PCR) and Western blot. The median of plasma C3a level was 82·83 ng/ml and 66·17 ng/ml in elective and spontaneous abortion patients, respectively. Medians of plasma C5a levels in elective and spontaneous abortion patients were 0·96 ng/ml and 1·14 ng/ml, respectively. Only plasma C5a levels but not C3a levels showed significant elevation in spontaneous abortion patients compared to elective abortion patients. Further, there was a threefold decrease in the mRNA expressions of complement inhibitory proteins CD46 and CD55 in the decidua obtained from spontaneous abortion patients compared to that of elective abortion patients. These data suggested that dysregulated complement cascade may be associated with spontaneous abortion.

Muscle inflammation induces a rapid increase in calcitonin gene-related peptide (CGRP) mRNA that temporally relates to CGRP immunoreactivity and nociceptive behavior

Recent data support an important role for calcitonin gene-related peptide (CGRP) in deep tissue nociceptive processing. Using real-time reverse transcriptase polymerase chain reaction (RT-PCR), radioimmunoassay, immunohistochemistry and behavioral testing, we studied the early time course of CGRP mRNA and protein expression as well as nociceptive behavior following muscle inflammation. A rapid and significant increase in CGRP mRNA occurred in the mandibular division (V3) of the ipsilateral trigeminal ganglion at 30 minutes, 4 and 24 h after the injection of complete Freund's adjuvant as an inflammatory agent into rat masseter muscle. No change in mRNA occurred in the ipsilateral ophthalmic and maxillary divisions (V1/V2) or in the contralateral V3. The levels of immunoreactive calcitonin gene-related peptide (iCGRP) in the ipsilateral V3 significantly increased at 1, 4 and 24 h following muscle inflammation. In contrast, no change occurred in iCGRP levels in either the ipsilateral V1/V2 or contralateral V3. When saline was injected into the masseter muscle, the levels of mRNA or iCGRP did not change in the ipsilateral V3 suggesting that the biochemical changes are specific to CFA-induced muscle inflammation. The number of muscle afferent neurons immunoreactive for CGRP was significantly reduced compared with control at 1, 4 and 24 h in the ipsilateral but not in the contralateral trigeminal ganglion following inflammation. This decrease in the ipsilateral ganglion may indicate a loss of intrasomatic CGRP as a result of increased axonal transport away from the neuronal cell body and/or release of CGRP. Behavioral testing showed a reduction in head withdrawal thresholds bilaterally from 30 min through 24 h following muscle inflammation. Thus upregulation of CGRP mRNA and iCGRP levels are temporally related to the development of inflammation and lowered pain thresholds. The present data support the hypothesis that CGRP is upregulated during deep tissue inflammation and suggest that gene transcription is involved in this upregulation.

Calcitonin gene-related peptide stimulates human villous trophoblast cell differentiation in vitro

Calcitonin gene-related peptide (CGRP) is a multifunctional peptide present in both maternal and fetal circulations in pregnancy. Its receptors have been identified on human trophoblast cells, but the role of CGRP in trophoblast differentiation remains unknown. This study was designed to determine the effect of CGRP on the differentiation of villous trophoblasts isolated from normal human term placentae. The morphological and functional differentiation of the trophoblast cells were assessed by desmosomal protein immunofluorescent staining and the quantification of hCG, estrogen and progesterone secretion. Results showed that (i) exposure of villous trophoblast cells to CGRP led to a dose-dependent increase in intracellular cyclic adenosine monophosphate (cAMP) accumulation; (ii) immunofluorescent staining with antidesmosomal antibody was identified at the boundaries between aggregated cytotrophoblast cells, and these stainings disappeared when cells fused to form syncytiotrophoblast cells; (iii) the formation of multinucleated syncytiums in primary cultured cytotrophoblasts was stimulated by CGRP as evidenced by the changes in antidesmosomal staining; (iv) CGRP increases trophoblast hCG secretion in a time- and dose-dependent manner, and this secretion was blocked by CGRP antagonist, CGRP(8-37), and (v) both 17beta-estradiol (E(2)) and progesterone concentrations in the culture medium were increased by CGRP, and these increases were dose dependent. These observations suggest that CGRP may be involved in the morphological and functional differentiation of trophoblast cells, and these actions might be attributed to CGRP-induced intracellular cAMP accumulation.

Effects of Parathyroid Hormone Like Hormone (PTHLH) Antagonist, PTHLH7–34, on Fetoplacental Development and Growth During Midgestation in Rats1

Parathyroid hormone-like hormone (PTHLH) secretion has been reported in human amnion, chorion, decidual cytotrophoblast, syncytiotrophoblast, endometrium, and myometrium; however, the functions of PTHLH during pregnancy, particularly during placenta formation and fetal development, are not well understood. We examined whether neutralization of PTHLH action using PTHLH antagonist, PTHLH(7-34), in rats during early gestation affects fetal and placental growth. Rats received s.c. a daily dose of either 0, 4, 12, or 36 microg of PTHLH(7-34) infused continuously through mini-osmotic pumps from Day 8 through Day 15 of pregnancy. Fetal weights measured on Day 15 were significantly decreased in rats treated with all the doses of PTHLH(7-34) compared to controls, and decreases in placental weights were significant at the 12-microg dose. TUNEL assay demonstrated an increased number of apoptotic cells in placenta of treated rats, including rats treated with the 4-microg dose. Cleaved caspase 3 (CASP3), caspase 9 (CASP9) (P < 0.05) and poly-ADP-ribose polymerase (PARP1) (P < 0.01) expression was increased and BCL2 (P < 0.01) expression was decreased in rats treated with 4 microg PTHLH(7-34) compared to that in control. Placental cytochrome c expression was increased (P < 0.01) in cytosolic and decreased (P < 0.01) in mitochondrial fraction in PTHLH(7-34)-treated rats. Caspase 8 expression was not affected by the treatment. Immunohistochemical analysis of platelet endothelial cell adhesion molecule (PECAM1) showed higher staining intensity in control than in treated rats. In conclusion, these results suggests that PTHLH plays a role in early pregnancy, and that antagonization of PTHLH action causes fetoplacental growth restriction through activation of mitochondrial pathway of apoptosis in the placenta and through decreased expression of PECAM1.

Dra/AfaE adhesin of uropathogenic Dr/Afa+ Escherichia coli mediates mortality in pregnant rats

Escherichia coli bearing adhesins of the Dr/Afa family frequently causes urogenital infections during pregnancy in humans and has been associated with mortality in pregnant rats. Two components of the adhesin, Dra/AfaE and Dra/AfaD, considered virulence factors, are responsible for bacterial binding and internalization. We hypothesize that gestational mortality caused by Dr/Afa+ E. coli is mediated by one of these two proteins, Dra/AfaE or Dra/AfaD. In this study, using afaE and/or afaD mutants, we investigated the role of the afaE and afaD genes in the mortality of pregnant rats from intrauterine infection. Sprague-Dawley rats, on the 17th day of pregnancy, were infected with the E. coli afaE+ afaD and afaE afaD+ mutants. The clinical E. coli strain (afaE+ afaD+) and the afaE afaD double mutant were used as positive and negative controls, respectively. The mortality rate was evaluated 24 h after infection. The highest maternal mortality was observed in the group infected with the afaE+ afaD+ strain, followed by the group infected with the afaE+ afaD strain. The mortality was dose dependent. The afaE afaD double mutant did not cause maternal mortality, even with the highest infection dose. The in vivo studies corresponded with the invasion assay, where the afaE+ strains were the most invasive (afaE+ afaD strain > afaE+ afaD+ strain), while the afaE mutant strains (afaE afaD+ and afaE afaD strains) seemed to be noninvasive. This study shows for the first time that the afaE gene coding for the AfaE subunit of Dr/Afa adhesin is involved in the lethal outcome of gestational infection in rats. This lethal effect associated with AfaE correlates with the invasiveness of afaE+ E. coli strains in vitro.

Mesenteric arterial relaxation to calcitonin gene-related peptide is increased during pregnancy and by sex steroid hormones

The present study investigated whether pregnancy and circulatory ovarian hormones increase the sensitivity of the mesenteric artery to calcitonin gene-related peptide (CGRP)-induced relaxation and possible mechanisms involved in this process. Mesenteric arteries from young adult male rats or female rats (during estrous cycle, after ovariectomy, at Day 20 of gestation, or Postpartum Day 2) were isolated, and the responsiveness of the vessels to CGRP was examined with a small vessel myograph. The CGRP (10(-10) to 10(-7) M) produced a concentration-dependent relaxation of norepinephrine-induced contractions in mesenteric arteries of all groups. Arterial relaxation sensitivity to CGRP was significantly (P < 0.05) greater in female rats compared with male rats. Pregnancy increased the sensitivity to CGRP significantly (P < 0.05) compared to ovariectomized and Postpartum Day 2 rats. In pregnant rats, CGRP-receptor antagonist, CGRP(8-37), inhibited the relaxation responses produced by CGRP. The CGRP-induced relaxation was not affected by N(G)-nitro-l-arginine methyl ester (nitric oxide inhibitor, 10(-4) M) but was significantly (P < 0.05) attenuated by an inhibitor of guanylate cyclase (1H-[1 , 2 , 4 ]oxadizaolo[4 , 3 -a]quinoxalin-1-one, 10(-5) M). Relaxation responses of CGRP on mesenteric arteries were blocked (P < 0.05) by a cAMP-dependent protein kinase A inhibitor, Rp-cAMPs (10(-5) M). The CGRP-induced vasorelaxation was significantly (P < 0.05) attenuated by calcium-dependent (tetraethylammonium, 10(-3) M), but not ATP-sensitive (glybenclamide, 10(-5) M), potassium channel blocker. Therefore, the results of the present study suggest that mesenteric vascular sensitivity to CGRP is higher during pregnancy and that cAMP, cGMP, and calcium-dependent potassium channels appear to be involved. Therefore, we propose that CGRP-mediated vasodilation may be important to maintain vascular adaptations during pregnancy.

Female Sex Steroid Hormones and Pregnancy Regulate Receptors for Calcitonin Gene-Related Peptide in Rat Mesenteric Arteries, but Not in Aorta1

Calcitonin gene-related peptide (CGRP) is a potent vasodilator neuropeptide known to be involved in the regulation of vascular tone. Results of previous studies from our laboratory and others suggest that vascular sensitivity to CGRP is enhanced during pregnancy and that the female sex steroid hormones estradiol-17beta (E2) and progesterone (P4) may be involved in this process. We hypothesized that CGRP receptors in the mesenteric artery are increased during pregnancy and with sex steroid hormone treatments. In the present study, we investigated whether pregnancy and female sex steroid hormones modulate the CGRP-receptors CGRP-A and CGRP-B in the mesenteric artery in the rat. The CGRP-A receptor consists of calcitonin receptor-like receptor (CRLR) and receptor activity-modifying protein 1 (RAMP1); however, the CGRP-B receptor needs to be further characterized. Messenger RNA levels for CRLR and RAMP1 were assessed by reverse transcription-polymerase chain reaction, and CGRP-B receptor proteins levels were determined by Western blot analysis. In addition, [125I]CGRP binding was measured by Scatchard analysis. Both mRNA for CGRP-A (CRLR and RAMP1) and the protein for CGRP-B receptors in mesenteric arteries were increased with pregnancy compared to nonpregnant, diestrous animals. A P4 antagonist, RU-486, downregulated and P4 upregulated these receptors in mesenteric arteries (P < 0.05) in pregnant rats. In adult ovariectomized rats, P4 upregulated CRLR and RAMP1 mRNA levels as well as [125I]CGRP-binding sites. The CGRP-B-receptor protein levels were significantly (P < 0.05) elevated by P4 and by combined E2 and P4 treatment. Together with earlier findings, these data suggest that increases in the expression of CGRP-A (CRLR and RAMP1) and CGRP-B receptors in mesenteric arteries may be important in reducing vascular resistance and in vascular adaptations that occur during pregnancy; in addition, P4 may be involved in this process.

Studies on the effects of the N-terminal domain antibodies of calcitonin receptor-like receptor and receptor activity-modifying protein 1 on calcitonin gene-related peptide-induced vasorelaxation in rat uterine artery

The vascular relaxation sensitivity to calcitonin gene-related peptide (CGRP) is enhanced during pregnancy, compared with nonpregnant human and rat uterine arteries. In the rat uterine artery, two types of CGRP receptors have been shown to coexist, CGRP-A receptor, which is a complex of calcitonin receptor-like receptor (CRLR), and receptor activity-modifying protein (RAMP(1)) and CGRP-B receptor, which is different from CRLR. In the present study, we hypothesized that: 1) CGRP-induced vasorelaxation in rat uterine artery is mediated through CGRP-A receptor and 2) N-terminal (Nt) domain of CRLR (Nt-CRLR) has a major contribution in ligand binding and mediating CGRP- induced relaxation effects in rat uterine artery. Polyclonal antibodies against Nt-domain of CRLR and RAMP(1) (Nt-RAMP(1)) were raised in rabbits and characterized for their specificity and were used to inhibit CGRP-induced vasorelaxation in rat uterine artery. For vascular relaxation studies, uterine arteries from Day 18 pregnant rats were isolated, and responsiveness of the vessels to CGRP was examined with a small vessel myograph. CGRP (10(-10) to 10(-7) M) produced a concentration-dependent relaxation of norepinephrine-induced contractions in Day 18 pregnant rat uterine arteries. These effects were significantly (P < 0.05) inhibited when uterine arteries were incubated with the antibody raised against Nt-CRLR (PD(2) = 6.75 +/- 0.20) and were totally abolished in presence of antibodies for both Nt-CRLR and Nt-RAMP(1) (PD(2) = 6.14 +/- 0.35). In contrast, a monoclonal antibody for CGRP-B receptor had no effect on CGRP-induced rat uterine artery relaxation. These studies suggest that CGRP effects in rat uterine artery are mediated through CGRP-A receptor and that Nt-domain of CRLR may play a predominant role in CGRP binding and thus in causing CGRP-induced uterine artery relaxation.

Mechanisms involved in calcitonin gene-related Peptide-induced relaxation in pregnant rat uterine artery

Human and rodent studies have demonstrated that calcitonin gene-related peptide (CGRP), a potent vasodilator, relaxes uterine tissue during pregnancy but not during labor. The vascular sensitivity to CGRP is enhanced during pregnancy, compared to nonpregnant human uterine arteries. In the present study, we hypothesized that uterine artery relaxation effects of CGRP are enhanced in pregnant rats compared to nonpregnant diestrus rats (NP-DE) and that several secondary messenger systems are involved in this process. We also hypothesized that the expression of CGRP-A receptor components, calcitonin receptor-like receptor (CRLR), receptor activity-modifying protein (RAMP1), and CGRP-B receptors are greater in pregnant rats. For vascular relaxation studies, uterine arteries from either NP-DE or Day 18 pregnant rats were isolated, and responsiveness of the vessels to CGRP was examined with a small vessel myograph. CGRP-A and CGRP-B receptor expressions were assessed by RT-PCR and Western immunoblotting, respectively. CGRP (10(-10)--10(-7) M) produced a concentration-dependent relaxation of norepinephrine-induced contractions in both NP-DE and Day 18 pregnant rat uterine arteries. Pregnancy increased the vasodilator sensitivity to CGRP significantly (P < 0.05) compared to NP-DE rats. CGRP receptor antagonist, CGRP8-37, inhibited CGRP-induced relaxation of pregnant uterine arteries. The CGRP-induced relaxation was not affected by NG-nitro-l-arginine methyl ester (L-NAME) (nitric oxide inhibitor, 10(-4) M) but was significantly (P < 0.05) attenuated by inhibitors of guanylate cyclase (ODQ, 10(-5) M) and adenylate cyclase (SQ 22536, 10(-5) M). CGRP-induced vasorelaxation was significantly (P < 0.05) attenuated by potassium channel blockers KATP (glybenclamide, 10(-5) M) and K(CA) (tetraethylammonium, 10(-3) M). The expression of CRLR and RAMP1 was significantly (P < 0.05) elevated during pregnancy compared to nonpregnant diestrus state (NP-DE). However, CGRP-B receptor proteins in uterine arteries were not altered with pregnancy compared to those of NP-DE. These studies suggest that CGRP-induced increases in uterine artery relaxation may play a role in regulating blood flow to the uterus during pregnancy and, therefore, in fetal growth and survival.

Changes in the expression of calcitonin receptor-like receptor, receptor activity-modifying protein (RAMP) 1, RAMP2, and RAMP3 in rat uterus during pregnancy, labor, and by steroid hormone treatments

Calcitonin gene-related peptide (CGRP) and its related peptide, adrenomedullin (AM), are potent smooth muscle relaxants in a variety of tissues. The CGRP has been reported to play an important role in maintaining uterine relaxation during pregnancy. We have previously reported that CGRP-induced uterine relaxation was gestationally regulated. Calcitonin receptor-like receptor (CRLR), a seven-domain transmembrane protein functions as CGRP-A receptor, in association with receptor activity-modifying protein (RAMP) 1, a single-domain transmembrane protein, whereas CRLR and RAMP2 or RAMP3 constitute a receptor for AM. In the present investigation, we examined the mRNA expression of CRLR, RAMP1, RAMP2, and RAMP3 in rat uterus (n = 8) by reverse transcriptional analysis and polymerase chain reaction to assess the changes in the expression of CGRP-A- and AM-receptor components during pregnancy and labor and by steroid hormone treatments in adult ovariectomized rats. The changes in mRNA are expressed relative to the 18S mRNA in the uterus of rats at various stages: nonpregnant, pregnant on Day 18, spontaneous labor at term, Day 2 postpartum, and in pregnant rats on treatment with RU486. Ovariectomized rats treated for 3 days twice daily s.c. with estradiol-17beta (2.5 microg/injection), progesterone (2 mg/injection), and the combination of estradiol-17beta and progesterone (same doses as above) were also examined for the expression of various receptor components. Results showed that mRNA expression of the receptor components was significantly higher (P < 0.001 for CRLR, P < 0.01 for RAMP1, P < 0.05 for RAMP2, and P < 0.01 for RAMP3) in pregnant compared to nonpregnant rats. Except for RAMP3, expression of all the other three genes decreased significantly (P < 0.05) during labor. A progesterone antagonist, RU486 significantly decreased (P < 0.01 for CRLR, P < 0.05 for RAMP1, RAMP2, and RAMP3) all the receptor components during pregnancy. In adult ovariectomized rats, progesterone caused significant increases in CRLR (P < 0.001), RAMP1 (P < 0.05), and RAMP2 (P < 0.01). Levels of RAMP3 were unaffected by the progesterone treatment. Estradiol-17beta treatment decreased all of the four receptor components significantly (P < 0.01 for CRLR, P < 0.05 for RAMP1, RAMP2, and RAMP3). Our results demonstrate that both CGRP and AM may play a role in uterine quiescence during pregnancy and that their receptor components are regulated by the steroid hormones.

Expression of calcitonin gene-related peptide receptor components, calcitonin receptor-like receptor and receptor activity modifying protein 1, in the rat placenta during pregnancy and their cellular localization

Calcitonin gene-related peptide (CGRP), one of the most potent endogenous vasodilators known, has been implicated in vascular adaptations and placental function during pregnancy. The present study was aimed to investigate mRNA expression of CGRP-A receptor components, calcitonin receptor-like receptor (CRLR) and receptor activity modifying protein 1 (RAMP(1)) in the rat placenta. Immunohistochemical staining of rat placentas obtained on day 18 of pregnancy using polyclonal anti-CRLR and RAMP(1) antibodies revealed that labelling was specifically concentrated in the cytotrophoblast and syncytium in labyrinth, trophoblastic giant cells and basophilic cells in trophospongial cell layer, and endothelium and smooth muscle cells in fetal vessels. The intensity of staining was reduced in all these cells except in the syncytium in placentas obtained during labour. RT-PCR analysis showed that mRNA expression of CRLR and RAMP(1) was significantly higher in the rat placenta from gestation day 17 to day 22, than during labour. During pregnancy, 17beta-estradiol inhibits, while progesterone stimulates, placental mRNA and proteins for CRLR and RAMP(1). Antiestrogen, ICI 182780, increased, whereas antiprogesterone, RU 486, inhibited the expression of both CRLR and RAMP(1). In summary, we demonstrate the presence and cellular localization of CRLR and RAMP(1) in the rat placenta. Elevated placental CRLR and RAMP(1) may be involved in CGRP-related increases in blood flow and therefore fetal growth and decreases at term labour may help minimize the blood loss.

Sex steroid hormones enhance hypotensive effects of calcitonin gene-related Peptide in aged female rats

The aim of the present study is to investigate whether vascular protective effects of steroid hormones in aged female rats are mediated through calcitonin gene-related peptide (CGRP), a known potent vasodilator. This rat model reflects the postmenopausal state in humans. We examined whether blood pressure lowering effects of CGRP are enhanced in aged female rats when steroid hormone treatments are administered. We observed that 1) continuous infusion of CGRP lowered blood pressures in rats treated with estradiol-17beta and progesterone (P < 0.05), 2) acute hypotensive effects of CGRP were significantly (P < 0.05) greater in the presence of steroid hormones than in vehicle-treated groups, 3) blood pressure decreases in response to CGRP are lower in aged female rats than they are in young adult ovariectomized rats, and 4) age-related differences in the hypotensive effects of CGRP were nullified when animals were treated with steroid hormones. These data suggest that female sex steroid hormones may modulate arterial blood pressure by regulating the CGRP effector system in female rats regardless of age.

Effects of pregnancy and female sex steroid hormones on calcitonin gene-related peptide content of mesenteric artery in rats

Calcitonin gene-related peptide (CGRP) levels in plasma and the dorsal root ganglia (DRG) are increased during pregnancy and in ovariectomized rats injected with ovarian hormones. Vasodilatory responses to CGRP are also increased in these animals. In the present study, we hypothesized that pregnancy and ovarian hormones elevate the contents of CGRP in perivascular nerves. We assessed CGRP-dependent mesenteric vascular relaxation induced by electrical field stimulation (EFS) and arterial content of CGRP. Because the mesenteric artery represents resistance vessels, segments of mesenteric arteries collected from female rats at different stages of the estrous cycle, pregnancy, or postpartum and from male rats were used in this study. The EFS-induced relaxation in the presence and absence of CGRP(8-37), an antagonist of CGRP, was used to measure CGRP-dependent relaxation, and radioimmunoassay (RIA) of tissue homogenates was used to assess changes in CGRP content in mesenteric branch arteries. The results show that CGRP-dependent, EFS-induced relaxation response was lower in female rats at diestrus and proestrus than in male rats, and no statistically significant differences were observed between Gestational Day 20 and Postpartum Day 2. The RIA revealed significantly lower mesenteric artery CGRP levels in female rats at proestrus, gestation, and postpartum than in female rats at diestrus or in male rats. We conclude that no correlation exists between CGRP-dependent, EFS-induced relaxation and CGRP content in the mesenteric arteries of these animal groups. Because both CGRP levels in DRG and serum are reported to be elevated, the reduced CGRP content in the vasculature during pregnancy and proestrus implicate enhanced basal release of CGRP at the nerve terminal in these animals.

Infusion of pregnant rats with calcitonin gene-related peptide (CGRP)(8-37), a CGRP receptor antagonist, increases blood pressure and fetal mortality and decreases fetal growth

Calcitonin gene-related peptide (CGRP) is the most potent endogenous vasodilatory peptide, and is involved in the regulation of blood flow to vital organs. We have previously shown that CGRP may be involved in vascular adaptations that occur during pregnancy, and that steroid hormones may be involved in these mechanisms. We hypothesized that endogenous CGRP is required for maintaining blood pressure and fetoplacental growth in pregnant rats, and that progesterone will enhance CGRP effects. The vasodilatory effects of CGRP are known to be inhibited by a competitive CGRP receptor antagonist, the C-terminal fragment CGRP(8-37). In the present study, we investigated whether continuous s.c. infusion of CGRP(8-37) to pregnant rats will reduce fetoplacental growth and increase systolic blood pressure. We also assessed whether progesterone will alter the effects of CGRP(8-37) on blood pressure during postpartum. Groups of five pregnant rats were s.c. infused with varying doses of CGRP(8-37) from Day 17 of pregnancy. Daily systolic blood pressures, pup weight, mortality at term delivery, and fetoplacental weights on Day 20 of gestation were measured. CGRP(8-37) at a dose of 0.083 mg day(-1) kg(-1) body weight (BW) showed no effects; however, doses of 0.33 and 1.33 mg day(-1) kg(-1) BW increased (P < 0.05) blood pressure during pregnancy, and these elevated blood pressures persisted during postpartum with the highest dose used. Progesterone (2 mg per injection, twice a day; s.c.) treatment significantly elevated blood pressure in rats infused with CGRP(8-37) during postpartum, suggesting that progesterone regulates CGRP-induced vascular effects. CGRP(8-37) infusion caused significant reductions in pup weight with an increase in mortality rate, and these effects were dose-dependent. Placental and fetal weights were also decreased prior to term on Day 20 of gestation, 72 h after CGRP(8-37) infusion, indicating effects on uteroplacental tissues. Therefore, we suggest that endogenous CGRP plays an important role in maintaining normal fetoplacental development, fetal survival, and vascular adaptations during pregnancy.

Gestational changes in calcitonin gene-related peptide, nerve growth factor, and its receptors in rat dorsal root ganglia

In dorsal root ganglia (DRG) cell cultures, levels of calcitonin gene-related peptide (CGRP) are increased in the presence of ovarian hormones and nerve growth factor (NGF). In addition, injection of ovariectomized rats with ovarian hormones led to an increase in levels of two NGF receptors, TrkA and p75(NTR), in DRG. Thus, we hypothesized that increased levels of ovarian hormones during pregnancy may elevate the synthesis of CGRP and NGF receptors in the DRG. DRG harvested from rats on specific days of pregnancy, on Day 2 postpartum, and after ovariectomy were subjected to radioimmunoassay, Western blot analysis, and NGF immunoassay to determine levels of CGRP, TrkA and p75(NTR), and NGF, respectively. CGRP levels in rat DRG were significantly higher during pregnancy than at Day 2 postpartum or in ovariectomized rats. Levels of both TrkA and p75(NTR) in DRG increased during pregnancy and remained elevated at Day 2 postpartum, but CGRP levels declined. Levels of NGF reached a statistically significant peak at Day 18 of gestation, and were not significantly reduced at Day 2 postpartum. Increased levels of ovarian steroid hormones during pregnancy may be involved in the synthesis of CGRP, however, the postpartum decreases in CGRP synthesis appear to be unrelated to NGF and its receptors.

Pregnancy and steroid hormones enhance the systemic and regional hemodynamic effects of calcitonin gene-related peptide in rats

Calcitonin gene-related peptide (CGRP) is a potent vasodilator neuropeptide known to be involved in the regulation of vascular resistance. Several lines of evidence suggest that CGRP plays a role in the vascular adaptations that occur during normal pregnancy; however, the effects of exogenous CGRP on systemic and regional hemodynamics during pregnancy remain unknown. Therefore, the purpose of this study was to determine the hemodynamic effects of systemically administered CGRP in adult pregnant (Day 19) and ovariectomized (ovx) rats using the radioactive microsphere technique. In addition, we also used ovariectomized rats treated for 3 days with estradiol (E2), progesterone (P4), E2 + P4 in sesame oil, or oil only to assess if these hormones regulate the CGRP-induced hemodynamic changes. On the day of study, catheters were inserted into the left cardiac ventricle (through the right carotid artery), right jugular vein, and caudal tail artery. Hemodynamic studies using radioactive microspheres were then performed in conscious rats 3 h after recovery from anesthesia. Blood pressure and heart rate were continuously monitored, and left ventricular pressure was determined immediately prior to each microsphere injection. Microspheres labeled with either (141)Ce or (85)Sr were injected prior to and 2 min following the i.v. bolus injection of CGRP (270 pmol/kg body weight [BW]). Mean arterial pressure (MAP) and total vascular resistance in pregnant rats was lower than in ovx rats, and this was further decreased with an i.v. bolus injection of 270 pmol CGRP/kg BW. Cardiac output was elevated with further increases upon CGRP administration in pregnant but not in ovx rats. The CGRP-induced changes in MAP, total vascular resistance, and cardiac output in E2 + P4 -treated rats were similar to that observed in Day 19 pregnant rats, indicating that CGRP effects on these parameters during pregnancy may be modulated by steroid hormones. Both pregnancy and E2 + P4 treatment in ovx rats caused significant decreases in CGRP-induced resistance in mesenteric, coronary, and renal vasculature. Thus, the vasodilatory sensitivity to CGRP during pregnancy may be mediated through decreased total vascular resistance, particularly to coronary, mesenteric, and renal vascular beds. Thus, CGRP-induced vasodilatory effects may play a role in mediating vascular adaptations that occur during pregnancy and that steroid hormones may modulate these CGRP effects.

Differential expression of uterine NO in pregnant and nonpregnant rats with intrauterine bacterial infection

Previous studies have demonstrated that nitric oxide (NO) is involved in the uterine host defense against bacterial infection. In nonpregnant rats, NO production in the uterus was shown to be lower, and inducible NO synthase (NOS) expression was undetectable. However, studies in pregnant rats show abundant expression of inducible NOS with significant elevation in NO production in the uterus. We have recently reported that intrauterine Escherichia coli infection caused a localized increase in uterine NO production and inducible NOS expression in the nonpregnant rat. In our present study, we examined whether the uterine NO production, NOS expression, and uterine tumor necrosis factor-alpha protein are increased in pregnant rats with intrauterine pathogenic Escherichia coli infection. Unlike the nonpregnant state, the NO production in the infected uterine horn of pregnant rats was not significantly elevated after bacterial inoculation compared with the contralateral uterine horn. The expression of uterine NOS (types II and III) also did not show significant upregulation in the infected horn. This is in contrast to that in nonpregnant animals, in which type II NOS was induced in the uterus on infection. Moreover, intrauterine infection induced an elevated expression of tumor necrosis factor-alpha protein in the infected horn both of nonpregnant and of pregnant rats. These data suggest that the sequential stimulation of NOS expression, especially the inducible isoform, and generation of uterine NO are lacking during pregnancy despite an elevated tumor necrosis factor-alpha after infection. In summary, NO synthesis response may be maximal at pregnancy, and infection may not further induce the NO system. Present studies, together with our previous report that intrauterine infection-induced lethality in pregnancy rats was amplified with the inhibition of NO, suggest that pregnancy is a state predisposed for increased complications associated with intrauterine infection and that the constitutively elevated uterine NO during pregnancy may help contain or even reduce the risk of infection-related complications.

Female steroid hormones modulate receptors for nerve growth factor in rat dorsal root ganglia

Calcitonin gene-related peptide (CGRP) is a vasodilatory peptide, and it is primarily synthesized in dorsal root ganglia (DRG). Plasma CGRP levels increase during pregnancy and with steroid hormones, and nerve growth factor (NGF) stimulates calcitonin/CGRP promoter and CGRP synthesis in DRG. We previously showed that CGRP levels in DRG were stimulated with steroid hormone treatments in vivo but not in vitro. Thus, the stimulation of CGRP by these hormones may be indirect through the upregulation of NGF effects. We hypothesized that the female sex steroid hormones upregulate NGF receptors, trkA and p75(NTR), in DRG. We examined the effects of 17 beta-estradiol (E(2)) and progesterone (P(4)) on NGF receptors in DRG obtained from ovariectomized (ovx) rats. Groups of 4 ovx rats were injected s.c. with 5 microg E(2), 4 mg P(4), or 5 microg E(2) + 4 mg P(4) in 0.2 ml sesame oil or injected with oil only and were killed at 6, 24, and 48 h. In addition, ovx rats were also injected s.c. with varying doses (0.2, 1.0, 5.0, 25 microg) of E(2) (0.5, 1.5, 4, 10 mg) P(4), and (5 microg) E(2) + (0.5, 1.5, 4.0, 10 mg) P(4) in 0.2 ml sesame oil, or vehicle, and killed at 6 (for E(2)) or 24 (for P(4) and E(2) + P(4)) h. Furthermore, groups of ovx rats were also killed at 12 and 24 h; 3 and 7 days; 2, 4, and 6 wk after ovariectomy. The DRGs were collected from all groups and then processed for Western immunoblotting to examine both trkA and p75(NTR) levels. Estradiol increased trkA at 6 h but not p75(NTR). Progesterone caused upregulation of trkA and p75(NTR) at 6 and 24 h. 17 beta-Estradiol + P(4) increased trkA at 6 and 24 h and p75(NTR) at all time points examined. One microgram of E(2) increased trkA but did not affect p75(NTR) levels. Progesterone at 4 and 10 mg upregulated trkA but only 10 mg P(4) increased p75(NTR). Five micrograms of E(2) coinjected with P(4) at 1.5 and 4 mg increased trkA, while p75(NTR) receptor was upregulated when coinjected with P(4) at 1.5 to 10 mg. The ovariectomy caused a decrease in trkA receptors compared to proestrus rats, and these decreases were significant by 6 wk, but surprisingly p75(NTR) increased at 2 wk after ovariectomy. 17 beta-Estradiol increased trkA but not p75(NTR) receptors in DRG, whereas P(4) caused increases in both trkA and p75(NTR) in DRG. In addition, the combination of these steroid hormones had more effect on both receptors than either hormone alone. Thus, we concluded that high levels of female steroid hormones such as those due to pregnancy or hormonal replacement therapy could increase NGF receptor expression in DRG that carry more NGF to elevate the CGRP synthesis in these groups. We suggested that the regulation of NGF receptors by ovarian steroids may underlie steroidal regulation of other factors such as CGRP.

Increased nitric oxide synthase activity and expression in the human uterine artery during pregnancy

Evidence exists that NO plays a role in the vasodilation that occurs during pregnancy. The purpose of the present study was to determine whether the role of NO is associated with an increase in the activity and protein expression of NO synthase (NOS) in the human uterine artery. Uterine arteries were obtained from pregnant patients (P arteries) and nonpregnant patients (NP arteries). NOS activity was estimated with the L-[(3)H]-arginine-to-L-[(3)H]-citrulline conversion method and on the basis of changes in tissue levels of cGMP. Western immunoblotting and immunohistochemistry were used to assess NOS protein expression. Ca(2+)-dependent NOS activity was 8 times greater (P:<0.01) in P than in NP arteries. Although most of this pregnancy-induced increase in NOS activity was Ca(2+) dependent (64%), a considerable portion was Ca(2+) independent. Expressions of endothelial NOS (eNOS) and neuronal NOS, but not inducible NOS, were demonstrated in P and NP arteries. The eNOS was located in the endothelium and stained with a qualitative order of P arteries>NP arteries (follicular)>NP arteries (luteal). The neuronal NOS was located in the adventitia of P and NP arteries. Basal NO-dependent and bradykinin-stimulated levels of cGMP were higher (P:<0.05) in P than in NP arteries. These results indicate that an upregulation of eNOS protein expression could account for the increased NO synthesis/release in the human uterine artery during pregnancy.

Estradiol-17beta inhibits nitric oxide synthase (NOS)-II and stimulates NOS-III gene expression in the rat uterus

Nitric oxide (NO) is synthesized by NO synthases (NOS) from L-arginine in a variety of tissues, including rat uterus. Progesterone was shown to be required for maintaining elevated NOS II expression in pregnant rat uterus. However, effects of estrogens on uterine NOS II expression remains unclear. In the present study, we examined whether 17beta-estradiol regulates NO production and NOS II expression in the rat uterus during pregnancy and in nonpregnant rats treated with lipopolysaccharide (LPS). Rats on Day 18 of pregnancy received 17beta-estradiol (0.5 or 5 microgram/rat). Groups of ovariectomized (ovx) rats received 17beta-estradiol (5 microgram/rat) or LPS (1 mg/rat) or a combination of the two or received vehicle only. All rats were sacrificed 24 h after treatments. Nitrite concentrations in uterine cultures were measured by Greiss reaction. Uterine NOS II and NOS III proteins and mRNA levels were determined by Western blotting and reverse transcription polymerase chain reaction, respectively. In the pregnant rat, estradiol administration caused inhibition in total NO production, suppression of both mRNA and protein levels of NOS II enzyme, and increase in NOS III mRNA and protein levels in the uterus in a dose-dependent manner. The data indicate that estradiol inhibits NOS II and total NO generation and stimulates NOS III expression. In ovx rats, LPS stimulated NOS II mRNA and NO production by the uterus. Coadministration of 5 microgram estradiol profoundly suppressed NOS II mRNA and NO generation but elevated NOS III mRNA. Thus, estradiol inhibited LPS-induced increases in NOS II mRNA. Estradiol inhibits NO production by NOS II through the inhibition of NOS II expression in the rat uterus. This inhibition of NOS II expression occurs whether NOS II expression is constitutive (pregnancy) or induced (LPS-treated nonpregnant). Estradiol inhibition of NOS II expression occurs in the presence (pregnancy) or absence (ovx) of progesterone. Estradiol may play a role in regulating NOS II expression and NO production and uterine contractility during pregnancy and labor.

Frequency-dependent effect of nitric oxide donor nitroglycerin on bone

Recently, we showed that supplementation with nitric oxide (NO) via donor nitroglycerin (NG) alleviated the ovariectomy and corticosteroid-induced bone loss in rats. In humans, high doses or frequent applications of NG (i.e., for angina) lead to rapid loss of its efficacy in relieving angina. To examine whether there is a similar effect on the loss of efficacy of NG on bone, we examined the frequency-dependent effects of NG on bone mineral density (BMD), bone mass, trabecular bone volumes (BV/TV), and blood pressure in rats. Thirty 7-month-old female Brown Norway rats underwent ovariectomy, and an additional six rats were sham-operated. The ovariectomized rats were treated either with vehicle (ovariectomized control), 17beta-estradiol (E2; positive control), or 0.2 mg NG (via dermal application) once, twice, or three times a day. Before and at the end of the 10-week treatment period, BMD of the lumbar spine was measured by dual-energy X-ray absorptiometric (DXA) scanning and expressed as a percentage change. BMD in ovariectomized rats was significantly lower (-2.5 +/- 2.0%) compared with the sham-operated rats (+6.3 +/- 5.3%; p < 0.01). Estrogen therapy completely abolished the ovariectomy-induced potential bone loss (+5.9 +/- 3.4%). Application of NG once daily also completely prevented (+6.2 +/- 2.8%; p < 0.01) the ovariectomy-induced bone loss (i.e., it was as effective as estrogen). However, the beneficial effects of NG on BMD were significantly reduced with increased frequency of application of NG (+1.9 +/- 2.1%, twice a day and -0.2 +/- 3.3% three times a day). Estrogen or once daily administration of NG preserved femur weights, BV/TV, and decreased urinary deoxypyridinoline levels as expected. However, a higher level of serum osteocalcin and bone-specific alkaline phosphatase levels were maintained only with once daily administration of NG. There were no adverse effects of these doses of NG on blood pressure, but a tendency to lower blood pressure was noticed with increased frequency of NG. These results confirmed our previous findings that NO donors counteract the bone loss associated with estrogen deficiency. However, these beneficial effects of maintaining BMD are lost with increased frequency of NG application.

Distinct regulation of nitric oxide and cyclic guanosine monophosphate production by steroid hormones in the rat uterus

It has previously been reported that uterine nitric oxide (NO) production is enhanced during rat pregnancy compared to non-pregnant, labouring or postpartum states. The present hypothesis is that these changes in uterine NO production during pregnancy are caused by the interplay of oestrogen and progesterone. It is further postulated that changes in cyclic guanosine monophosphate (cGMP) production closely follow the changes in uterine NO synthesis. To test these hypotheses a variety of hormonal regimens (17beta-oestradiol, progesterone and combinations) were applied to different rat models (prepubertal, non-pregnant intact and ovariectomized as well as pregnant rats). The production of nitric oxide (NO) as well as basal and in-vitro NO-stimulated cGMP tissue content were measured in parallel. NO production was measured by the accumulation of nitrites and nitrates in a 24 h incubation medium as analysed by Greiss reaction. cGMP content was measured by radioimmunoassay. Diethylenetriamine/NO (DETA/NO) was used as NO donor. NO production in the rat uterus was markedly increased by pregnancy compared to other physiological (prepubertal, or cycling dioestrus) and experimentally induced (OVX) states. In contrast, uterine cGMP was significantly decreased in pregnancy. Pregnancy also inhibited the elevation in uterine cGMP after in-vitro NO challenge. Chronic 17beta-oestradiol treatment in prepubertal and/or OVX models increased NO production and also mimicked the effect of pregnancy on cGMP. Administration of progesterone in prepubertal rats induced a parallel decrease in both uterine NO and cGMP. In conclusion, sex steroid hormones distinctly regulate uterine NO and cGMP production depending upon the dose and regimen used, as well as the animal's reproductive state.

Regulation of calcitonin gene-related peptide expression in dorsal root ganglia of rats by female sex steroid hormones

Calcitonin gene-related peptide (CGRP), a potent vasodilator primarily synthesized in dorsal root ganglia (DRG) neurons, has been shown to decrease vascular resistance and thus regulate blood flow to a variety of organs in rats. Serum CGRP levels in the human have been reported to increase with pregnancy and decrease postpartum. It has been suggested that female sex steroid hormones play a role in cardiovascular function, but the mechanisms are unknown. In this study, we examined the effects of estradiol-17beta (E(2)) and progesterone (P(4)) on the expression of CGRP in DRG in adult rats both in vivo and in vitro. Ovariectomized (ovx) animals were injected s.c. with 5 microg E(2), 4 mg P(4), or 5.0 microg E(2) + 4 mg P(4) in 0.5 ml sesame oil or with oil only, and groups of 4 rats were killed at 0, 24, or 48 h. DRGs were then removed and analyzed for CGRP mRNA and immunoreactive (i-)CGRP content by Northern blotting and RIA, respectively. Primary cultures of DRG neurons from adult female rats were used to assess the effects of varying doses of E(2) (1, 10, 100 nM), P(4) (10, 100, 1000 nM), or E(2) (10 nM) + P(4) (100 nM) in the absence or presence of nerve growth factor (NGF; 20 ng/ml); and CGRP mRNA content in the cells and i-CGRP in the medium were quantitated at 24 or 48 h after incubation. Results of in vivo studies showed that E(2) caused a significant increase in CGRP mRNA at 24 h (1.8-fold) and in i-CGRP levels both at 24 h (2. 8-fold) and at 48 h (3.4-fold) in DRG of ovx rats. P(4) also stimulated expression of both CGRP mRNA and i-CGRP. In the in vitro studies, either E(2) or P(4) alone or the two in combination were without effect on CGRP expression in cultured DRG neurons at all the doses tested. However, in the presence of NGF, both CGRP mRNA and peptide levels were significantly enhanced by E(2), P(4), and E(2)+P(4) in a time-dependent (2.0- to 2.8-fold at 24 h, 3.0- to 5. 0-fold at 48 h) and dose-dependent manner, with maximal effects achieved at 1.0 nM (E(2)) and 100 nM (P(4)) at 24 h of incubation. In summary, both E(2) and P(4), either alone or in combination, stimulate CGRP peptide synthesis in DRG neurons through increasing CGRP mRNA. The effects of these steroid hormones are mediated through amplifying the NGF-induced synthesis of CGRP in these neurons. Thus, we propose that the cardiovascular functions of female sex steroid hormones may be mediated, at least in part, by the up-regulation of neuronal CGRP synthesis, via NGF-mediated mechanisms.

Pregnancy and sex steroid hormones enhance circulating calcitonin gene-related peptide concentrations in rats

Calcitonin-gene-related peptide (CGRP) is a 37 amino acid neuropeptide synthesized primarily in dorsal root ganglia (DRG) and distributed widely in the perivascular nerves, suggesting that this peptide may play a role in the regulation of peripheral vascular tone. Since female sex steroid hormones have been implicated in the regulation of peripheral vascular tone during pregnancy, we postulated that they may alter the concentration of CGRP in the circulation and thus modulate the increased blood flow observed during pregnancy. In the present study, we measured changes in plasma concentrations of CGRP in non-pregnant, pregnant, and post-partum rats. Groups of ovariectomized rats were treated s.c. for 3 days either with 17beta-oestradiol (2.5 microg per injection twice daily), progesterone (2 mg per injection twice daily), or vehicle. Another group of adult, non-pregnant rats at dioestrus stage of the oestrous cycle was also used in this study. Plasma concentrations of CGRP were higher (P < 0.05) in rats on day 19 of pregnancy (22.0 +/- 3.0 pmol/l) compared to that during delivery (5. 0 +/- 2.0), post-partum day 2 (2.0 +/- 0.7) or in non-pregnant (4.9 +/- 1.6) state. Furthermore, in adult ovariectomized (6.0 +/- 0.6) rats, plasma CGRP concentrations were increased significantly (P < 0. 05) by oestradiol (10.0 +/- 1.0), progesterone (9.5 +/- 1.0) and oestradiol + progesterone (14.0 +/- 1.0). Thus, circulating concentrations of CGRP are elevated during pregnancy and by oestrogen and progesterone, suggesting that the elevated concentrations of CGRP may play an important role in vascular adaptations that occur during pregnancy.

Pregnancy and exogenous steroid treatments modulate the expression of relaxant EP(2) and contractile FP receptors in the rat uterus

Prostaglandins (PGs) interact with specific receptors on plasma membranes to regulate myometrial activity in many species. The present study examined whether the expression of relaxant prostaglandin E receptor subtype two (EP(2)) and contractile prostaglandin F receptor (FP) mRNA in the rat uterus is changed during various states of pregnancy and regulated by steroid hormones. Expression of mRNA for EP(2) and FP receptors in the full-thickness uteri was analyzed by reverse transcription-polymerase chain reaction using specific primers. Abundance of receptor mRNA was expressed relative to beta-actin mRNA. Results showed that 1) mRNA for EP(2) receptors in the rat uterus was substantially increased during pregnancy (320%) compared with the nonpregnant state (100%, P < 0.01), and declined during labor at term (36% vs. 100% in control, P < 0.01); 2) mRNA expression for FP receptors in rat uterus was increased during pregnancy (333% vs. 100% in nonpregnant rats, P < 0. 01) and reached maximal levels during labor (515% vs. 100% in control, P < 0.01); 3) upon RU-486 treatment on Day 19 of pregnancy, uterine EP(2) receptor mRNA levels were decreased (18% vs. 100% in control, P < 0.01), and FP mRNA levels were increased (357% vs. 100% in control, P < 0.01); 4) with ICI 164384 (an antiestrogen) treatment on Day 19 of gestation, uterine FP receptor mRNA levels were decreased without effects on EP(2) receptors; 5) in ovariectomized (ovx) rats, progesterone increased EP(2) (163% vs. 100% in control, P < 0.01) and had no effects on FP receptor mRNA expression in the rat uterus; 6) estradiol increased FP receptor mRNA levels (358% vs. 100% in control, P < 0.01) and had no effects on EP(2) mRNA in the ovx rat uterus. Therefore, we conclude that steroid hormones modulate the mRNA for relaxant EP(2) and contractile FP receptors for PGs in the uterus and thus regulate uterine activity during pregnancy and labor.

Increased blood pressure in alpha-calcitonin gene-related peptide/calcitonin gene knockout mice

Nerves that contain calcitonin gene-related peptide (CGRP) are components of the sensory nervous system. Although these afferent nerves have traditionally been thought to sense stimuli in the periphery and transmit the information centrally, they also have an efferent vasodilator function. Acute administration of a CGRP receptor antagonist increases the blood pressure (BP) in several models of hypertension, which indicates that this potent vasodilator plays a counterregulatory role to attenuate the BP increase in these settings. To determine the role of this peptide in the long-term regulation of cardiovascular function, including hypertension, we obtained mice that have a deletion of the alpha-calcitonin gene-related peptide (alpha-CGRP) gene. Although the beta-calcitonin gene-related peptide (beta-CGRP) gene is intact in these mice, alpha-CGRP is by far the predominant species of CGRP produced in dorsal root ganglia (DRG) sensory neurons. Initially, we examined the effect of deletion of the alpha-CGRP on baseline BP and beta-CGRP and substance P mRNA expression. Systolic BP was significantly higher in the knockout mice (n=7) compared with wild-type in both male (160+/-6.1 vs 125+/-4.8 mm Hg) and female (163+/-4.8 vs 135+/-33 mm Hg) mice. Next, groups (n=7) of knockout and wild-type mice had catheters surgically placed in the right carotid artery for mean arterial pressure recording. With the animals fully awake and unrestrained, the knockout mice displayed an elevated mean arterial pressure compared with wild-type in both male (139+/-4.9 vs 118+/-4.9 mm Hg) and female (121+/-3.4 vs 107+/-3.1 mm Hg) mice. Northern blot analysis of DRG RNA samples confirmed the absence of alpha-CGRP mRNA in the knockout mice. Substance P mRNA content in DRG was unchanged between the 2 groups; however, beta-CGRP mRNA levels were reduced 2-fold in the knockout mice. These results indicate for the first time that alpha-CGRP may be involved in the long-term regulation of resting BP and suggest that these mice are particularly sensitive to challenges to BP homeostasis because of the loss of a compensatory vasodilator mechanism.

Regulation of calcitonin gene-related peptide receptors in the rat uterus during pregnancy and labor and by progesterone

Calcitonin gene-related peptide (CGRP) is a potent smooth muscle relaxant in a variety of tissues. We recently demonstrated that CGRP relaxes uterine tissue during pregnancy but not during labor. In the present study we examined whether uterine (125)I-CGRP binding and immunoreactive CGRP receptors are regulated by pregnancy and labor and by sex steroid hormones. We found that (125)I-CGRP binding to membrane preparations from uteri was elevated during pregnancy and decreased during labor and postpartum. Changes in immunoreactive CGRP receptors were similar to the changes in (125)I-CGRP binding in these tissues, suggesting pregnancy-dependent regulation of CGRP receptor protein. CGRP receptors were elevated by Day 7 of gestation, and a precipitous decrease in these receptors occurred on Day 22 of gestation prior to the onset of labor. Both (125)I-CGRP-binding and immunofluorescence studies indicated that CGRP receptors were localized to myometrial cells. Hormonal control of uterine CGRP receptors was assessed by the use of antiprogesterone RU-486, progesterone, and estradiol-17beta. RU-486 induced a decrease in uterine CGRP receptors during pregnancy (Day 19). On the other hand, progesterone prevented the fall in uterine CGRP receptors at term (Day 22). In addition, progesterone also increased uterine CGRP receptors in nonpregnant, ovariectomized rats, while estradiol had no effects. These hormone-induced changes in uterine CGRP receptors were demonstrated by (125)I-CGRP-binding, Western immunoblotting, and immunolocalization methods. These results indicate that CGRP receptors and CGRP binding in the rat uterus are increased with pregnancy and decreased at term. These receptors are localized to the myometrial cells, and progesterone is required for maintaining CGRP receptors in the rat uterus. Thus, the inhibitory effects of CGRP on uterine contractility are mediated through the changes in CGRP receptors and may play a role in uterine quiescence during pregnancy.

Localized increase in nitric oxide production and the expression of nitric oxide synthase isoforms in rat uterus with experimental intrauterine infection

OBJECTIVE

We recently reported that nitric oxide was associated with increased mortality among pregnant rats with intrauterine infection. In our current study we investigated the expression of different isoforms of nitric oxide synthases and nitric oxide in the nonpregnant rat uterus with experimental intrauterine infection.

STUDY DESIGN

Pathogenic Escherichia coli was inoculated into the uterine lumen of ovariectomized rats. Animals were killed after inoculation, and uterine horns were collected for assessing nitric oxide production with high-performance liquid chromatography and nitric oxide synthase (type II and type III) protein expression with Western immunoblotting and immunofluorescence methods.

RESULTS

(1) Nitric oxide production increased in the infected uterine horn in a time-dependent manner after intrauterine infection but did not increase in the uninfected horn. (2) Nitric oxide synthase type III protein contents did not show a difference between infected and uninfected horns, and type III nitric oxide synthase was expressed by the epithelial cells and smooth muscle cells. (3) Type II nitric oxide synthase was abundantly expressed in infected horns but was not expressed in uninfected horns. Immunofluorescence data indicated that macrophages and natural killer cells, located in the endometrial layer clustering around epithelial cells, expressed type II protein.

CONCLUSION

We suggest that localized increase in type II nitric oxide synthase expression and nitric oxide production occurs in response to intrauterine infection and that the nitric oxide system may play a role in host response to restrict the infection.

Involvement of calcitonin gene-related peptide in the modulation of human myometrial contractility during pregnancy

Calcitonin gene-related peptide (CGRP) is a potent vasodilator and relaxes smooth muscle of a variety of tissues, but the effects of CGRP on human myometrial contractions and the changes in CGRP receptors (CGRP-Rs) in human myometrium have not been described. We report that CGRP induced dose-dependent relaxation in spontaneously contracting myometrium from pregnant women. This relaxation effect is diminished in myometrium obtained from patients during labor and in the nonpregnant state. CGRP-induced relaxations are inhibited by a CGRP-R antagonist (CGRP(8-37)), a soluble guanylate cyclase inhibitor (LY(83583)), and a nitric oxide synthase inhibitor (L-NAME). Both Western blotting and mRNA analysis showed that CGRP-Rs are present in human myometrium, and that the expression of these receptors is increased during pregnancy and decreased during term labor. Immunofluorescent staining revealed that CGRP-Rs are abundant in the myometrial cells of pregnant women who are not in labor, and are minimal in uterine specimens from women in labor and in the nonpregnant state. We conclude that increased CGRP-Rs in myometrium, and resulting enhanced myometrial sensitivity to CGRP, may play a role in maintaining human myometrium in a quiescent state during pregnancy, and that a decline in the CGRP-Rs at term could contribute to the initiation of labor.

Inverse relationship between severity of experimental pyelonephritis and nitric oxide production in C3H/HeJ mice

The contribution of nitric oxide to host resistance to experimental pyelonephritis is not well understood. We examined whether the inhibition of nitric oxide synthesis alters the sensitivity of lipopolysaccharide (LPS) responder (C3H/HeN) and nonresponder (C3H/HeJ) mice to experimental Escherichia coli pyelonephritis. C3H/HeJ and C3H/HeN mice were implanted subcutaneously with minipumps containing an inhibitor of nitric oxide, NG-nitro-L-arginine methyl ester (L-NAME), or a corresponding vehicle. Ascending urinary tract infection by bladder catheterization with two strains of E. coli, an O75 strain bearing Dr fimbriae and an O75 strain bearing P fimbriae, was developed in tested animals. Twenty-four hours following bladder infection, the kidneys of C3H/HeN and C3H/HeJ mice were colonized at a similar rate. However, 5 weeks postinoculation, C3H/HeN mice cleared infection while C3H/HeJ mice showed persistent colonization. Twenty-four hours following infection, C3H/HeN mice treated with L-NAME showed no significant increase of renal tissue infection compared to the saline-treated control group. However, L-NAME-treated C3H/HeJ mice showed an approximately 100-fold increase in E. coli infection rate compared to the saline-treated controls in the Dr+ group but showed no change compared to those in the P+ group. Dissemination of Dr+ E. coli but not P+ E. coli to the liver and uterus was significantly enhanced with L-NAME treatment in C3H/HeJ mice only. Nitric oxide had no direct killing effect on E. coli in vitro. Nitrite production by various organs was found to be significantly lower in C3H/HeJ mice than in C3H/HeN mice. Alteration of nitric oxide and LPS responsiveness was significantly associated with the increased sensitivity of C3H/HeJ mice to experimental Dr+ but not to P+ E. coli pyelonephritis. These findings are consistent with the hypothesis that nitric oxide synthase activity in concert with LPS responsiveness may participate in the antibacterial defense mechanisms of the C3H mouse urinary tract. This phenomenon is strain dependent and possibly related to the invasive properties of E. coli.

Pregnancy and steroid hormones enhance the vasodilation responses to CGRP in rats

We recently reported that calcitonin gene-related peptide (CGRP) reversed the hypertension induced by nitric oxide inhibition in pregnant rats and that this effect appeared to be progesterone dependent. In the present study, we examined whether the vasodilator responses to CGRP are increased during pregnancy and whether these responses are steroid hormone dependent. Three groups of ovariectomized (Ovx) rats (n = 4-8 rats/group) were studied 3 days after daily treatment (subcutaneous injection) with progesterone (P; 2 mg/injection, twice daily for 3 days, in 0.2 ml of sesame oil), 17beta-estradiol (E; 2.5 microgram/injection, twice daily for 3 days, in 0.2 ml of sesame oil), or vehicle (sesame oil). A fourth group (n = 6 rats) of pregnant rats was studied on day 19 of gestation. A fifth group of adult, nonpregnant rats (n = 6 rats), regardless of stage of estrous cycle, was also used in this study. Mean arterial blood pressure (MAP) was continuously monitored in fully awake and free-moving instrumented rats. MAP was measured before and after administration of either saline or varying bolus doses of CGRP (9-360 pmol/kg body wt). CGRP produced a dose-dependent decrease in MAP in all rats with a significant (P < 0.05) reduction in MAP beginning with a CGRP dose of 90 pmol/kg and with maximal effects observed at 360 pmol/kg. Decreases in MAP in response to CGRP were significantly (P < 0.05) greater in pregnant compared with nonpregnant rats. Similarly to pregnant rats, Ovx rats given both E and P treatments produced greater decreases in MAP in response to CGRP at 90, 180, and 360 pmol/kg doses compared with both ovary-intact and Ovx nonpregnant rats, which were not different from each other. In summary, these data show that 1) the hypotensive effects of CGRP are dose dependent and 2) the hypotensive effects of CGRP are enhanced during pregnancy and in Ovx rats treated with either E or P. Therefore, we suggest that the decrease in vascular tone that is seen during pregnancy may be mediated, at least in part, by a sex steroid hormone-induced increase in the vascular sensitivity to the vasodilator effects of CGRP.

Nitric oxide reverses prostaglandin-induced inhibition in ovarian progesterone secretion in rats

The present studies were undertaken to determine whether nitric oxide (NO) is involved in the regulation of ovarian progesterone and oestradiol secretion in rats. Immature female Sprague-Dawley rats at 27 days of age were injected s.c. with 4 IU pregnant mare's serum gonadotrophin (PMSG) and were killed 72 h after the injection. The ovaries were collected, weighed and cultured in Dulbecco's modified Eagle's medium containing saline, NO donor, NO synthesis inhibitor or prostaglandin F2 alpha (PGF2 alpha). After 24 h culture, the medium concentrations of progesterone and oestradiol were measured by radioimmunoassay. Results showed that: (i) diethylenetriamine (DETA)/NO (1 x 10(-6), 1 x 10(-5), 1 x 10(-4) M), an NO donor, caused a dose-dependent increase in progesterone synthesis (355 +/- 43, 443 +/- 46, 647 +/- 55 ng/g ovary respectively, P < 0.01) with a concomitant decrease in ovarian oestradiol secretion (408.1 +/- 50.7, 272.9 +/- 28.2, 132.6 +/- 34.6 pg/g ovary respectively, P < 0.01); (ii) neither progesterone nor oestradiol concentrations in the culture medium were altered by DETA without NO; (iii) NG-nitro-l-arginine methyl ester (1 x 10(-4) M), an inhibitor of NO synthesis, did not significantly affect progesterone and oestradiol secretion by rat ovaries; (iv) PGF2 alpha(1 x 10(-6) M) caused a fall in progesterone and oestradiol synthesis; (v) co-incubation with DETA/NO, significantly reversed the PGF2 alpha-induced decrease in progesterone concentrations from 184 +/- 29 to 388 +/- 60 ng/g (P < 0.01), but not that of oestradiol. It can be concluded that NO up-regulates progesterone secretion and down-regulates oestradiol secretion in rat ovaries, and NO can reverse PGF2 alpha-induced inhibition in ovarian progesterone secretion.

Regulation of inducible nitric oxide synthase messenger ribonucleic acid expression in pregnant rat uterus

Nitric oxide synthases catalyze the synthesis of the biomediator, nitric oxide, from L-arginine in a variety of tissues. The expression and regulation of inducible isoform of nitric oxide synthase (NOS II) in the uterus were assessed in this study by reverse transcription-polymerase chain reaction with the use of specific primers. Results showed the following: 1) NOS II mRNA expression in the rat uterus was substantially increased during pregnancy and decreased during labor at term; 2) RU-486 (an antagonist of progesterone) induced preterm labor and was associated with a marked decrease in NOS II mRNA expression to 60.9%, 20.3%, and 2.9% at, respectively, 6, 12, and 24 h after treatment compared with the control value (100%); 3) progesterone administration in pregnant rats significantly increased uterine NOS II gene expression (374.1% vs. 100%); 4) NOS II mRNA in the uterus was significantly reduced by prostaglandin F2alpha (PGF2alpha; 11.6% vs. 100% in control); 5) treatment with progesterone prevented PGF2alpha-induced inhibition in NOS II mRNA expression; 6) ICI 164384, an antiestrogen, significantly increased serum progesterone concentration and stimulated NOS II expression by the uterus in a time-dependent manner; 7) as shown by immunofluorescent studies, cells stained by NOS II antibodies were apparent in the decidual compartment as well as in areas between myometrial cell bundles in the pregnant rat uterus. The density of staining decreased in the specimens at labor and postpartum. We conclude that NOS II gene expression in the rat uterus was enhanced during pregnancy and decreased during labor and postpartum. NOS II in rat uterus is up-regulated by progesterone and down-regulated by estrogens and prostaglandins, consistent with their role in uterine activity regulation during pregnancy and labor.

Pre-eclamptic toxemia: potential new therapy based on animal studies

OBJECTIVE

Pre-eclamptic toxemia (PET) affects 4 to 8% of human pregnancies. Presently, reliable specific therapies to treat this disorder are not available. This study was designed to develop a new therapeutic approach in the management of PET using an animal model.

DESIGN

Pregnant rats (5/group) infused with 50 mg L-NAME daily via osmotic mini pumps from day 17 of gestation developed a PET-like syndrome. Systolic blood pressure (BP) was monitored daily during pregnancy and up to 7 days postpartum by the tail cuff method. Pup weight and mortality were recorded immediately after delivery. We examined the effect of CGRP to ameliorate L-NAME-induced hypertension during pregnancy, and the efficacy of CGRP and progesterone in combination to inhibit L-NAME-induced hypertension during the post-partum period.

RESULTS

Blood pressure in L-NAME-treated rats was significantly elevated (P < 0.01) throughout pregnancy (141 +/- 3 to 166 +/- 10 mm Hg). CGRP 10 micrograms/day did not cause hypotension, the values being similar to controls which received only saline. On the other hand, CGRP infusion inhibited L-NAME-induced hypertension to normotensive levels (116 +/- 3 to 122 +/- 2) during pregnancy (up to day 22 of gestation), but not during postpartum period (137 +/- 8 to 148 +/- 2). During the post-partum period, neither progesterone nor CGRP by itself was effective in lowering L-NAME-induced hypertension. The combination of CGRP with progesterone decreased BP to control levels in the post-partum period, and also significantly improved foetal mortality and growth (P < 0.05).

CONCLUSIONS

CGRP inhibited L-NAME-induced hypertension during pregnancy and not during postpartum period. The same phenomenon was evident in the presence of adequate levels of progesterone in the post-partum period. We believe that CGRP regulates vascular adaptations during pregnancy and these effects may be progesterone-dependent. This combination treatment of CGRP plus progesterone may be a promising therapy in the management of PET in humans.

Uterine relaxation responses to calcitonin gene-related peptide and calcitonin gene-related peptide receptors decreased during labor in rats

OBJECTIVES

Our purpose was to investigate (1) whether uterine relaxation responses to calcitonin gene-related peptide are differentially regulated during pregnancy and labor, (2) the involvement of nitric oxide in smooth muscle relaxant action of calcitonin gene-related peptide in the rat uterus, (3) whether receptors for calcitonin gene-related peptide are expressed in rat uterus, and if so (4) whether the concentrations of these receptors are differently regulated during pregnancy and labor.

STUDY DESIGN

Rats were killed on day 18 of gestation, at the time of spontaneous labor, or postpartum day 2. The uteri were removed for in vitro contractility measurements, nitric oxide production, and calcitonin gene-related peptide receptor binding assay.

RESULTS

(1) Calcitonin gene-related peptide induced a dose-dependent relaxation in spontaneously contracting uterine strips from pregnant rats on day 18 of gestation; (2) the relaxation effects of calcitonin gene-related peptide on the uterus were decreased during spontaneous delivery at term and post partum compared with that during pregnancy; (3) calcitonin gene-related peptide-induced relaxation was inhibited by pretreatment of the uterine tissue with a calcitonin gene-related peptide receptor antagonist, calcitonin gene-related peptide(8-37); (4) nitric oxide synthesis inhibitor (N(G)-nitro-L-arginine methyl ester) and soluble guanylate cyclase inhibitor (LY83583) significantly decreased calcitonin gene-related peptide-induced relaxation of the rat uterus during pregnancy; (5) calcitonin gene-related peptide increased the uterine nitric oxide production in pregnant rats, and this increase was obliterated in the presence of calcitonin gene-related peptide(8-37); and (6) calcitonin gene-related peptide receptors are present in rat uterus, and the concentration of these receptors dramatically increases during pregnancy and decreases during labor at term.

CONCLUSIONS

Calcitonin gene-related peptide inhibits uterine spontaneous contractions in rats during pregnancy but not during labor and post partum. The inhibitory effects of calcitonin gene-related peptide on uterine contractility appear to be modulated, at least in part, by the activation of nitric oxide generation in the rat uterus. Changes in calcitonin gene-related peptide receptors could contribute to the changes in calcitonin gene-related peptide-mediated uterine relaxation during pregnancy and labor.

Immunohistochemical localization of constitutive and inducible cyclo-oxygenases in rat uterus during the oestrous cycle and pregnancy

The uterus is a rich source of eicosanoids synthesized from arachidonic acid metabolism through the cyclo-oxygenase pathway. Two isoforms of cyclo-oxygenase, constitutive (COX-I) and inducible (COX-II) enzyme, have been reported. In the present study, we have immunohistochemically mapped the distribution of both COX-I and COX-II during various physiological states of the rat uterus. Uterine tissue was collected from female rats (a) during different stages of the oestrous cycle, (b) on days 1, 4, 8 and 18 of gestation, (c) after spontaneous delivery and (d) post partum, and fixed in Bouin's fixative. After paraffin wax embedding, 5-microm-thick sections were immunohistochemically stained by the ABC technique. Observation of the stained sections under the light microscope revealed that, in non-pregnant rat uterus, both COX-I and COX-II were abundantly expressed in the endometrium, with minimal staining observed in the myometrium. Staining was more prominent in epithelial cells than in stromal cells. The intensity of staining in epithelial cells was highest at pro-oestrus and oestrus and lowest at dioestrus. In pregnant rats, although the expression of both COX-I and COX-II was localized primarily to the endometrium with very little staining in the myometrium on day 1 of gestation, both of these enzymes were also apparent in myometrial cells by day 4 of gestation. The staining intensity of endometrial and myometrial cells increased further with the progression of gestation, being maximal at the time of spontaneous delivery. During the post-partum period, however, the staining intensity for both of the enzymes in endometrium and myometrium was decreased. Thus, our studies show that the expression of cyclo-oxygenases in various uterine cells vary with the oestrous cycle and with pregnancy. Furthermore, prominent increases in the expression of cyclo-oxygenases in the myometrium during pregnancy and parturition imply that the cyclo-oxygenase system in the myometrium may play a major role in modulating uterine contractility during pregnancy and labour.

Nitric oxide inhibits development of embryos and implantation in mice

The objectives of this study were to evaluate the effects of a nitric oxide (NO) donor on embryo development in vitro and on implantation of embryos in vivo in mice. Mouse embryos (2-cell) were incubated in media containing different concentrations of diethylenetriamine/NO (DETA/NO), a nitric oxide donor, and development was monitored daily for 4 days. Specificity of NO effects was assessed by using DETA without NO or 48 h preincubated DETA/NO. In in-vivo studies, mated mice were continuously infused, subcutaneously, with various concentrations of DETA/NO or DETA through mini-osmotic pumps (from day 1 of pregnancy), and implantations in the uterus were assessed on day 6. None of the embryos progressed beyond 4-cell stage when exposed to 0.1 or 1.0 mM DETA/NO compared with 94.5% of control embryos that developed beyond the morula stage by day 4. Embryo development was unaffected by lower (0.001 and 0.01 mM) concentrations of DETA/NO, 48 h preincubated DETA/NO, or DETA only. Infusion of DETA/NO to mice caused inhibition of embryo implantation in a dose-dependent manner. No implantation sites were observed in mice infused with a daily dose of 20 micromol DETA/NO rate, compared with an implantation rate of 81.8% in control or DETA-treated mice. This study demonstrates for the first time that higher concentrations of NO inhibit both embryo development in vitro and implantation in vivo in mice.

Calcitonin Gene-related Peptide (CGRP) is a Mediator of Vascular Adaptations During Hypertension in Pregnancy

Hypertension during pregnancy is a serious obstetrical problem, and the pathophysiology of pre-eclampsia is unclear. Evidence is presented that calcitonin gene-related peptide (CGRP) plays a role in the vascular adaptations that occur during pregnancy. In addition, CGRP might be critical for compensatory vasodilatory changes that occur in response to hypertensive insults during pregnancy, and these compensatory mechanisms might require adequate progesterone activity. Thus, we suggest that an inadequate CGRP-mediated compensatory vasodilatory (adaptative) response may play a role in the pathophysiology of hypertensive disorders during pregnancy.

Role and regulation of nitric oxide in the uterus during pregnancy and parturition

OBJECTIVE

To review the English-language literature as it relates to the role and regulation of uterine nitric oxide (NO) during pregnancy and parturition, special emphasis being placed on the interactions of NO with other uterotonic agents.

METHODS

A thorough literature review of the English-language literature using a Medline search was performed.

RESULTS

Current data support the view that NO is generated in the uterus and inhibits uterine contractility. Gestation, parturition, steroid hormones, and prostaglandins modulate both the generation and the effects of NO on the uterus. The changes in NO and its effects are consistent with the theory that NO plays a role in uterine quiescence during pregnancy. A change in this system at term or preterm could play a role in inhibition of labor and delivery.

CONCLUSION

Uterine NO may play a role in maintaining uterine quiescence during pregnancy.

Involvement of nitric oxide pathway in prostaglandin F2 alpha-induced preterm labor in rats

OBJECTIVE

Our purpose was to investigate the roles of nitric oxide and prostaglandins in controlling parturition.

STUDY DESIGN

Pregnant rats on day 18 of gestation were injected intraperitoneally with prostaglandin F2 alpha, prostaglandin F2 alpha plus diethylenetriamine-nitric oxide (a donor of nitric oxide), prostaglandin F2 alpha plus diethylenetriamine without nitric oxide, or vehicle. Uterine nitrite production, nitric oxide synthase messenger ribonucleic acid and contractile response in vitro, and serum progesterone levels were measured. The labor and delivery of the rats also were monitored.

RESULTS

Exogenously administered prostaglandin F2 alpha significantly inhibited nitric oxide production by the uterus in a time-dependent manner with maximal effects observed 48 hours after prostaglandin F2 alpha treatment. Messenger ribonucleic acid for inducible nitric oxide synthase but not endothelial nitric oxide synthase messenger ribonucleic acid in the uterus was significantly inhibited by prostaglandin F2 alpha with maximal inhibition at 48 hours after prostaglandin F2 alpha injection. The serum progesterone concentration was substantially reduced by prostaglandin F2 alpha, and this reduction was partially reversed by administration of diethylenetriamine-nitric oxide but not diethylenetriamine without nitric oxide. Prostaglandin F2 alpha caused increases in contractile activity of the uterus in a dose-dependent manner. Diethylenetriamine-nitric oxide (10(-4) mol/L) blocked prostaglandin F2 alpha-induced contractions. Premature parturition was induced within 48 hours after prostaglandin F2 alpha injection in 100% of the animals. Coadministration of diethylenetriamine-nitric oxide completely prevented the preterm labor induced by prostaglandin F2 alpha.

CONCLUSION

Prostaglandin F2 alpha inhibited inducible nitric oxide synthase messenger ribonucleic acid and subsequent nitric oxide generation in the rat uterus. Nitric oxide can prevent prostaglandin F2 alpha-induced preterm labor, possibly by attenuating the fall in serum progesterone and blocking uterine contractions induced by prostaglandin F2 alpha administration.

Lethal outcome of uterine infection in pregnant but not in nonpregnant rats and increased death rate with inhibition of nitric oxide

PROBLEM

Limited information is available on potential differences in sensitivity to urogenital infections between pregnant and nonpregnant hosts.

METHOD OF STUDY

In this study, we evaluated Escherichia coli infectious complications in pregnant and nonpregnant rats and the effect of nitric oxide (NO) inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), on the outcome of an experimental uterine infection.

RESULTS

Of the infected pregnant animals, 31% were found dead in 24-48 hr. The death rate was increased 2-fold (66%) with L-NAME treatment. No deaths occurred in nonpregnant animals with or without L-NAME treatment. The rate of uterine infection in pregnant animals was about 10-fold higher than in nonpregnant animals.

CONCLUSION

We propose that infectious complications of pregnancy may be related to gestation-dependent sensitivity to the pathogenic microorganism and the host NO status.

Prevention of corticosteroid-induced bone loss with nitric oxide donor nitroglycerin in male rats

Nitric oxide (NO) has been reported to inhibit osteoclastic bone resorption. We examined the bone sparing effect of NO on prevention of corticosteroid-induced bone loss in older male rats. Recently, we demonstrated that NO donor nitroglycerin (NG) can alleviate ovariectomy-induced bone loss, and the protective effects of estrogens on bone are mediated through NO [Bone 18(4):301-304; 1996]. Therefore, we chose to study a different model (i.e., steroid-induced osteoporosis in males) to evaluate whether NG can inhibit the bone loss associated with corticosteroid therapy. Twenty-five 32-week-old male Wistar rats were randomly assigned to five groups (n = 5/group). They received either vehicle, methylprednisolone (7 mg/kg per week), NO synthase inhibitor L-NAME (25 mg/kg per day), NO donor nitroglycerin (NG, 0.2 mg twice daily), a combination of prednisolone+NG, or prednisolone plus L-NAME, respectively. Prior to treatment and at the end of the 6 week treatment period, bone mineral density (BMD) of the lumbar spine was measured by dual energy X-ray absorptiometry scanning. Administration of prednisolone significantly decreased BMD (-9.50%, p < 0.05). The group receiving NG with prednisolone (-2.34%) and the group treated with NG alone (-0.36%) were not statistically different from the control group (-0.11%). Similar to the changes in BMD, femur weights were also significantly lower in prednisolone-treated rats (1.09 +/- 0.01 g vs. 1.17 +/- 0.03 in controls; p < 0.05). However, the rats receiving prednisolone together with NG were able to maintain their femur weights (1.13 +/- 0.02). There was a reduction of 9.5% of BMD (p < 0.05) and 7.8% of femoral weight (p < 0.05) in rats treated with L-NAME. A 50%-70% reduction of the percentage trabecular bone volume in the proximal tibia and distal femur and a 50% reduction of the midshaft cortical area was seen after corticosteroid therapy, and these too were prevented by administration of NG. Here, we demonstrate, for the first time, that supplementation with a NO donor compound can counteract prednisolone-induced bone loss.

Contrasting effects of diethylenetriamine-nitric oxide, a spontaneously releasing nitric oxide donor, on pregnant rat uterine contractility in vitro versus in vivo

OBJECTIVE

The aim of the study was to investigate the in vitro (on tension) and in vivo (on intrauterine pressure) effects of a spontaneously releasing nitric oxide adduct, diethylenetriamine-nitric oxide, on rat uterine contractility.

STUDY DESIGN

Contractile responses to the nitric oxide donor diethylenetriamine-nitric oxide on isometric tension of rat uterine strips (in vitro) and on intrauterine pressure (in vivo) in anesthetized and conscious animals were quantified at late gestation and during preterm and term labor. Preterm labor was induced with the administration of a single injection of the antiprogestin onapristone (10 mg). All control animals were injected with diethylenetriamine, the parent compound, without nitric oxide.

RESULTS

The nitric oxide donor diethylenetriamine-nitric oxide relaxes rat uterine tissues when given in vitro during gestation (median effective dose 0.30 +/- 0.09 mmol/L) but fails to have an effect on uterine tissues from laboring term and preterm animals in the muscle bath. Intraperitoneal injection of the nitric oxide adduct in doses of 5 mg and 50 mg produced a significant and sustained decrease in intrauterine pressure in both delivering and nondelivering animals compared with intrauterine pressure values before administration. Analysis of intrauterine pressure levels at different time frames (before injection, immediately after injection, and after 30, 60, and 90 minutes) in anesthetized rats between days 19 and 21 of gestation shows that the dose of 5 mg diethylenetriamine-nitric oxide significantly (p < 0.05) decreased contractility starling at 30 minutes after administration. Similarly, during labor diethylenetriamine-nitric oxide (5 mg intraperitoneally) decreased contractility (p < 0.05) but only starting at 60 minutes after injection. However, with the dose of 50 mg diethylenetriamine-nitric oxide contractility was reduced 30 minutes (p < 0.05) after treatment during pregnancy (days 19 to 21). The same dose of diethylenetriamine-nitric oxide produced a greater relaxation immediately after intraperitoneal injection (p < 0.05) in the laboring group. Diethylenetriamine-nitric oxide (50 mg) also induced an earlier onset and greater relaxation in animals delivering preterm compared with nondelivering animals at the same stage of gestation. The intrauterine pressure maintained constant contractility levels throughout the 100-minute recording period in the control groups of anesthetized and conscious animals that were injected with diethylenetriamine at the equivalent doses. In the preterm laboring group the effects were similar in both anesthetized and conscious animals.

CONCLUSION

Although in vitro studies of uterine muscle show decreased inhibitory responses to nitric oxide donors during spontaneous term labor and preterm labor compared with tissues collected during late pregnancy (day 19), studies in vivo demonstrate that nitric oxide donors can decrease uterine contractility even more effectively during delivery. The results suggest that nitric oxide donors may act indirectly or that the fetal-placental unit increases the availability of nitric oxide in vivo. Therefore, despite what in vitro studies alone suggest, nitric oxide donor drugs may be very effective in suppressing either term or preterm labor.

Rat GST 8-8 is expressed predominantly in myeloid origin cells infiltrating the gravid uterus

Previous studies from our laboratory have shown a relatively high expression of rGST8-8 in uterine tissues. This GST isozyme displays relatively high glutathione-peroxidase activity towards lipid-hydroperoxides and towards toxic 4-hydroxyalkenals generated from lipid peroxidation. Since the uterus is a unique organ, subject to oxidative stress due to infiltration by immune effector cells during gestation and because this infiltration is readily identifiable histologically, the studies reported herein were performed to localize the cell specific expression of rGST8-8 to determine whether immune effector cells infiltrating the pregnant rat uterus specifically expressed rGST8-8. A 75 bp end-radiolabeled cRNA probe was prepared from the full length mGSTA4-4 cDNA from the region which is highly homologous with rGST8-8. This cRNA probe was used for in situ hybridization studies to localize rGST8-8 in specific cell types of gravid rat uterus. Results of these studies indicate that this GST isozyme is selectively expressed in myeloid origin cells such as monocytes/macrophages, and neutrophils infiltrating the uterine endometrium and in vascular walls. Selective expression of rGST8-8 in the myeloid origin cells, which are known to generate higher levels of reactive oxygen species, suggests that this GST isozyme plays an important role in the protection mechanisms against lipid peroxidation.

Progesterone up-regulates vasodilator effects of calcitonin gene-related peptide in N(G)-nitro-L-arginine methyl ester-induced hypertension

OBJECTIVE

We recently reported that calcitonin gene-related peptide can reverse the hypertension produced by N(G)-nitro-L-arginine methyl ester in pregnant rats. In the current study we investigated whether these vasodilator effects of calcitonin gene-related peptide were progesterone dependent.

STUDY DESIGN

Calcitonin gene-related peptide or N(G)-nitro-L-arginine methyl ester was infused through osmotic minipumps, either separately or in combination, to groups of five pregnant rats from day 17 of gestation until day 8 post partum or to nonpregnant ovariectomized rats for 8 days. Progesterone was injected during days 1 to 6 post partum and for 6 days after ovariectomy. Systolic blood pressure was measured daily.

RESULTS

Animals receiving N(G)-nitro-L-arginine methyl ester exhibited significant elevations of blood pressure during pregnancy and post partum. Coadministration of calcitonin gene-related peptide to these rats reversed the hypertension during pregnancy but not during the postpartum period. At the dose used in this study calcitonin gene-related peptide administered alone was without significant effects on blood pressure. However, it reduced both the mortality and growth restriction of the fetus associated with N(G)-nitro-L-arginine methyl ester in these animals. Calcitonin gene-related peptide reversed the hypertension in N(G)-nitro-L-arginine methyl ester-infused postpartum rats during the periods of progesterone treatment only, and these effects were lost when progesterone treatment was stopped. Neither progesterone nor calcitonin gene-related peptide alone were effective. To further confirm these observations, progesterone effects were tested in ovariectomized adult rats. Similar to the findings in postpartum rats, calcitonin gene-related peptide completely reversed the elevation in blood pressure in N(G)-nitro-L-arginine methyl ester-treated rats receiving progesterone injections. The effects of calcitonin gene-related peptide were apparent only during the progesterone treatment period, and these effects were lost when progesterone treatment was stopped. Again, at these doses calcitonin gene-related peptide and progesterone were each ineffective alone.

CONCLUSIONS

Calcitonin gene-related peptide reverses the N(G)-nitro-L-arginine methyl ester-induced hypertension during pregnancy, when progesterone levels are elevated, but not post partum or in ovariectomized nonpregnant rats. The blood pressure-lowering effects of calcitonin gene-related peptide were restored in both postpartum and ovariectomized rats with progesterone treatment. Therefore we conclude that progesterone modulates vasodilator effects of calcitonin gene-related peptide in hypertensive rats.