Vascular hyperresponsiveness to adrenomedullin during pregnancy is associated with increased generation of cyclic nucleotides in rat mesenteric artery

Calcitonin Gene Related Peptide, Adrenomedullin, and Adrenomedullin 2 Function in Uterine Artery During Human Pregnancy

RATIONALE

Calcitonin gene-related peptide (CGRP) and its family members adrenomedullin (ADM) and adrenomedullin 2 (ADM2; also known as intermedin) support vascular adaptions in rat pregnancy.

OBJECTIVE

This study aimed to assess the relaxation response of uterine artery (UA) for CGRP, ADM, and ADM2 in nonpregnant and pregnant women and identify the involved mechanisms.

FINDINGS

(1) Segments of UA from nonpregnant women that were precontracted with U46619 (1μM) in vitro are insensitive to the hypotensive effects of CGRP, ADM, and ADM2; (2) CGRP, ADM, and ADM2 (0.1-100nM) dose dependently relax UA segments from pregnant women with efficacy for CGRP > ADM = ADM2; (3) the relaxation responses to CGRP, ADM, and ADM2 are differentially affected by the inhibitors of nitric oxide (NO) synthase (L-NAME), adenylyl cyclase (SQ22536), apamin, and charybdotoxin; (4) UA smooth muscle cells (UASMC) express mRNA for calcitonin receptor-like receptor (CRLR) and receptor activity modifying protein (RAMP)1 and RAMP2 but not RAMP3; (5) receptor heterodimer comprising CRLR/RAMP1 and CRLR/RAMP2 but not CRLR/RAMP3 is present in UA; (6) soluble fms-like tyrosine kinase (sFLT-1) and TNF-α treatment decrease the expression of RAMP1 mRNA (P < 0.05) in UASMC; and (7) sFLT-1 treatment impairs the association of CRLR with all 3 peptides while TNF-α inhibits the interaction of CGRP but not ADM or ADM2 with CRLR in UASMC (P < 0.05).

CONCLUSIONS

Relaxation sensitivity of UA for CGRP, ADM, and ADM2 is increased during pregnancy via peptide-specific involvement of NO system and endothelium-derived hyperpolarizing factors; vascular disruptors such as sFLT-1 and TNFα adversely impact their receptor system in UASMC.

Calcitonin Gene-Related Peptide Rescues Proximity Associations of Its Receptor Components, Calcitonin Receptor-Like Receptor and Receptor Activity-Modifying Protein 1, in Rat Uterine Artery Smooth Muscle Cells Exposed to Tumor Necrosis Factor Alpha

Calcitonin gene-related peptide (CALCB), adrenomedullin (ADM), and ADM2/intermedin play critical roles in vascular adaptation during pregnancy through calcitonin receptor-like receptor (CALCRL) and receptor activity-modifying proteins (RAMPs). This study was designed to assess the predominant RAMP that associates with CALCRL to form a functional receptor in the rat uterine artery smooth muscle (RUASM). We also determined if these receptor component associations are decreased by tumor necrosis factor (TNF) alpha and if CALCB, ADM, or ADM2 can rescue CALCRL/RAMP associations. Using proximity ligation assay in RUASM cells, this study shows that CALCRL predominantly associates with RAMP1 forming a CALCB receptor, and minimally with RAMP2 and RAMP3 that confer specificity for ADM and ADM2. However, knockdown of RAMP1 mRNA increases the interaction between CALCRL and RAMP3 without affecting the association of CALCRL and RAMP2. Furthermore, CALCB, ADM, and ADM2 have no effects on the associations of CALCRL with any of the RAMPs in RUASM cells. Interestingly, CALCB reverses the TNFalpha-induced decreases in CALCRL/RAMP1 associations. Furthermore, CALCB increases ERK1/2 phosphorylation in a time-dependent manner in RUASM, and the protective effect of CALCB on TNFalpha-induced inhibition of CALCRL/RAMP1 associations was significantly blocked in presence of ERK inhibitor (PD98059). In conclusion, this study demonstrates that CALCRL predominantly associates with RAMP1 forming a CALCB-specific receptor complex in RUASM cells, which is dissociated by TNFalpha. Rescue of TNFalpha-induced dissociation of CALCRL/RAMP1 complex by CALCB in RUASM cells suggests a potential use of CALCB in developing therapeutic strategies for pregnancy-related complications that are vulnerable to abnormal levels of TNFalpha, such as fetal growth restriction and preeclampsia.

Impaired Vasodilatory Responses of Omental Arteries to CGRP Family Peptides in Pregnancies Complicated by Fetal Growth Restriction

RATIONALE

Calcitonin gene-related peptide (CGRP), adrenomedullin (ADM), and adrenomedullin2 (ADM2)/intermedin are potent vasorelaxant peptides considered to play a role in the adaptive mechanisms in rat pregnancy through increased vasodilation in mesenteric and uterine artery.

OBJECTIVE

This study was designed to demonstrate the response of omental arteries (OA) to vasoactive peptides CGRP, ADM, and ADM2 in pregnancy complications such as fetal growth restriction (FGR), and assess the changes in the expression of their receptor components in segments of OA from FGR pregnancy compared to the control.

FINDINGS

The findings for this study are: 1) relaxation responses of OA were higher for bradykinin (78.55 ± 3.91 vs 52.67 ± 2.19; P < .05) in pregnancy with FGR compared to the normal, 2) relaxation response of OA segments to CGRP was similar with no change in the expression of G-protein couple receptor-calcitonin receptor-like receptor complex in normal healthy pregnancy and pregnancy complicated by FGR, 3) maximal relaxation response of OA were significantly (P < .05) lower for both ADM (18.2 ± 6.7 vs 38 ± 2.5) and ADM2 (26.9 ± 6.7 vs 48 ± 2.6) along with decreases in their respective ligand-receptor complex in FGR compared to the normal pregnancies, 4) expression of calcitonin receptor-like receptor mRNA was higher but its immunoreactivity was lower in OA from FGR pregnancy compared to the normal, and 5) mRNA and protein levels of RAMP1, RAMP2, and RAMP3 were lower in OA isolated from FGR pregnancies compared to the normal.

CONCLUSION

The current study demonstrates that FGR is associated with an increase in the sensitivity of OA to bradykinin and decreased sensitivity for ADM and ADM2 ligand-receptor system with no change in the response for CGRP compared to the normal healthy pregnancy, and suggests a potential role for ADM and ADM2 in the pathophysiology of maternal vasculature in FGR pregnancy.

Pregnancy Increases Relaxation in Human Omental Arteries to the CGRP Family of Peptides

Calcitonin gene-related peptide (CALCB) and its family members adrenomedullin (ADM) and intermedin (ADM2) play important roles in maintaining vascular adaptations during pregnancy in animal models. The present study was designed to evaluate the responses of omental arteries to CALCB, ADM, and ADM2 in pregnant and nonpregnant women, and to determine the mechanisms involved. By using resistance omental arteries collected from nonpregnant women (n = 15) during laparotomy and from term pregnant women (n = 15) at cesarean delivery, this study shows that the receptor components--calcitonin receptor-like receptor (CALCRL) and receptor activity-modifying proteins (RAMPs) 1, 2 and 3--are localized to endothelial and smooth muscle cells in omental arteries, with increased expressions of both mRNA and protein in pregnant compared with nonpregnant women. The myography study demonstrated that CALCB, ADM, and ADM2 (0.1-100 nM) dose dependently relax U46619 (1 muM) precontracted omental artery segments, and the maximum possible effects to CALCB and ADM2, but not to ADM, are significantly enhanced in pregnant compared with nonpregnant women. Further, the vasodilatory responses to CALCB, ADM, and ADM2 are reduced by inhibitors of nitric oxide (NO) synthase (L-NAME), adenylyl cyclase (SQ22536), voltage-activated potassium channels (4-aminopyrodin and tetrabutylammonium), Ca(2+)-activated potassium channel (charybdotoxin), and cyclooxygenase (indomethacin). In conclusion, the CALCB family of peptides, CALCB and ADM2, increase human omental artery relaxation during pregnancy through diverse mechanisms, including NO, endothelium-derived hyperpolarizing factors (EDHFs) and prostaglandins, and thus could contribute to the vascular adaptations during pregnancy in the human.

Involvement of Receptor Activity-Modifying Protein 3 (RAMP3) in the Vascular Actions of Adrenomedullin in Rat Mesenteric Artery Smooth Muscle Cells

CALCB, ADM, and ADM2 are potent vasodilators that share a seven-transmembrane GPCR, calcitonin receptor-like receptor (CALCRL), whose ligand specificity is dictated by the presence of one of the three receptor activity-modifying proteins (RAMPs). We assessed the relative pharmacologic potency of these peptides in mesenteric artery smooth muscle cells (VSMCs) and the specific RAMP that mediates the effect of ADM in VSMCs. VSMCs, with or without RAMP knockdown, were treated with CALCB, ADM, or ADM2 in the presence or absence of their antagonists, CALCB8-37, ADM22-52, and ADM217-47, respectively, to assess the relative effect of peptides on cAMP production and their pharmacologic potency. Proximity ligation assay was used to assess the specific RAMP that associates with CALCRL to mediate the actions of ADM in VSMCs. All three peptides induced cAMP generation in VSMCs and the order of their potency is CALCB > ADM > ADM2. Effects of CALCB were blocked by CALCB8-37, ADM effects were blocked by CALCB8-37 and ADM217-47 but not ADM22-52, and ADM2 effects were blocked by all three antagonists. Knockdown of RAMP2 was ineffective, whereas knockdown of RAMP3 inhibited ADM-induced cAMP production in VSMCs, suggesting involvement of RAMP3 with CALCRL to mediate ADM effects. Absence of both RAMP2 and RAMP3 further increased CALCB-induced cAMP synthesis compared to control (P < 0.05). ADM increased CALCRL and RAMP3 association and RAMP3 knockdown inhibited the interaction of ADM with CALCRL.

Fetal-derived adrenomedullin mediates the innate immune milieu of the placenta

The remodeling of maternal uterine spiral arteries (SAs) is an essential process for ensuring low-resistance, high-capacitance blood flow to the growing fetus. Failure of SAs to remodel is causally associated with preeclampsia, a common and life-threatening complication of pregnancy that is harmful to both mother and fetus. Here, using both loss-of-function and gain-of-function genetic mouse models, we show that expression of the pregnancy-related peptide adrenomedullin (AM) by fetal trophoblast cells is necessary and sufficient to promote appropriate recruitment and activation of maternal uterine NK (uNK) cells to the placenta and ultimately facilitate remodeling of maternal SAs. Placentas that lacked either AM or its receptor exhibited reduced fetal vessel branching in the labyrinth, failed SA remodeling and reendothelialization, and markedly reduced numbers of maternal uNK cells. In contrast, overexpression of AM caused a reversal of these phenotypes with a concomitant increase in uNK cell content in vivo. Moreover, AM dose-dependently stimulated the secretion of numerous chemokines, cytokines, and MMPs from uNK cells, which in turn induced VSMC apoptosis. These data identify an essential function for fetal-derived factors in the maternal vascular adaptation to pregnancy and underscore the importance of exploring AM as a biomarker and therapeutic agent for preeclampsia.

Adaptive changes of mesenteric arteries in pregnancy: a meta-analysis

The vascular response to pregnancy has been frequently studied in mesenteric artery models by investigating endothelial cell (EC)- and smooth muscle cell (SMC)-dependent responses to mechanical (flow-mediated vasodilation, myogenic reactivity, and vascular compliance) and pharmacological stimuli (G protein-coupled receptor responses: Gq(EC), Gs(SMC), Gq(SMC)). It is unclear to what extent these pathways contribute to normal pregnancy-induced vasodilation across species, strains, and/or gestational age and at which receptor level pregnancy affects the pathways. We performed a meta-analysis on responses to mechanical and pharmacological stimuli associated with pregnancy-induced vasodilation of mesenteric arteries and included 55 (188 responses) out of 398 studies. Most included studies (84%) were performed in Wistar and Sprague-Dawley rats (SDRs) and compared late gestation versus nonpregnant controls (80%). Pregnancy promotes flow-mediated vasodilation in all investigated species. Only in SDRs, pregnancy additionally stimulates both vasodilator Gq(EC) sensitivity (EC(50) reduced by -0.76 [-0.92, -0.60] log[M]) and Gs(SMC) sensitivity (EC(50) reduced by -0.51 [-0.82, -0.20] log[M]), depresses vasopressor Gq(SMC) sensitivity (EC(50) increase in SDRs by 0.23 [0.16, 0.31] log[M]), and enhances arterial compliance. We conclude that 1) pregnancy facilitates flow-mediated vasodilation at term among all investigated species, and the contribution of additional vascular responses is species and strain specific, and 2) late pregnancy mediates vasodilation through changes at the receptor level for the substances tested. The initial steps of vasodilation in early pregnancy remain to be elucidated.

GPCRs as potential therapeutic targets in preeclampsia

Preeclampsia is an important obstetric complication that arises in 5% of women after the 20(th) week of gestation, for which there is no specific therapy and no cure. Although much of the recent investigation in this field has focused on soluble forms of the angiogenic membrane receptor tyrosine kinase Flt1 and the transforming growth factor β co-receptor Endoglin, there is significant clinical potential for several GPCR targets and their agonists or antagonists in preeclampsia. In this review, we discuss several of the most promising candidates in this category, including calcitonin receptor-like receptor / receptor activity modifying protein 1 complexes, the angiotensin AT1, 2 and Mas receptors, and the relaxin receptor RXFP1. We also address some of the controversies surrounding the roles and therapeutic potential of these GPCRs and their (ant)agonists in preeclampsia.

Adrenomedullin relaxes rat uterine artery: mechanisms and influence of pregnancy and estradiol

Uterine arteries play a major role in regulating uteroplacental blood flow. Failure to maintain blood flow to the uteroplacental compartment during pregnancy often results in intrauterine growth retardation. Immunohistochemical staining of adrenomedullin (AM), an endogenous vasoactive peptide, in uterine artery was intense in pregnant compared to nonpregnant rats, but it is not known whether AM directly relaxes uterine artery or not. In this study, we elucidated the mechanisms of uterine artery relaxation by AM and its regulation by pregnancy and female sex steroids. AM was able to relax uterine artery, and this relaxation was influenced positively by pregnancy and estradiol as evidenced by the increased pD(2) and E(max) values of AM. Both pregnancy and estradiol treatment to ovariectomized rats amplified RAMP(3) expression in uterine arteries while progesterone had no effect. AM-induced uterine artery relaxation is predominantly endothelium-dependent. The AM receptor antagonist CGRP(8-37) is more potent than AM(22-52) in inhibiting the AM relaxation, indicating the involvement of AM(2) receptor subtype. Moreover, AM uses the classical nitric oxide-cyclic guanosine monophosphate pathway along with K(Ca) channels to mediate the vasodilatory effect in uterine artery. In conclusion, sensitivity of uterine artery to AM-induced relaxation is increased with pregnancy or estradiol treatment by increasing RAMP(3) expression, suggesting an important role for AM in regulating the uterine hemodynamics, probably maintaining uterine blood flow during pregnancy and in pre- and postmenopausal cardiovascular adaptation differences.

Protein restriction during pregnancy induces hypertension and impairs endothelium-dependent vascular function in adult female offspring

Intrauterine undernutrition plays a role in the development of adult hypertension. Most studies are done in male offspring to delineate the mechanisms whereby blood pressure may be raised; however, the vascular mechanisms involved in female offspring are unclear. Female offspring of pregnant Sprague-Dawley rats fed either a control (C; 18%) or a low-protein (LP; 6%) diet during pregnancy were used. Birth weight and later growth were markedly lower in LP than in C offspring. LP offspring exhibited impaired estrous cyclicity with increased mean arterial pressure. Hypotensive response to acetylcholine (ACh) and the hypertensive response to phenylephrine (PE) were greater in LP than in C rats. N-nitro-L-arginine methyl ester (L-NAME) induced greater hypertensive responses in C than in LP rats. Endothelium-intact mesenteric arteries from LP offspring exhibited increased contractile responses to PE and reduced vasodilation in response to ACh. In endothelium-denuded arteries, relaxation responses to sodium nitroprusside were similar in both groups. Basal and ACh-induced increase in vascular nitrite/nitrate production was lower in LP than in C offspring. L-NAME or 1H-1,2,4-oxadiazolo-4,3-quinoxalin-1-one inhibited ACh relaxations and enhanced PE contractions in C offspring, but had minimal effect in LP rats. The decreased NO-mediated vascular response might explain the increased vascular contraction and arterial pressure in female offspring with low birth weight.

Differential [Ca2+]i signaling of vasoconstriction in mesenteric microvessels of normal and reduced uterine perfusion pregnant rats

Vascular resistance and blood pressure (BP) are reduced during late normal pregnancy (Norm-Preg). In contrast, studies in human preeclampsia and in animal models of hypertension in pregnancy (HTN-Preg) have suggested that localized reduction in uterine perfusion pressure (RUPP) in late pregnancy is associated with increased systemic vascular resistance and BP; however, the vascular mechanisms involved are unclear. Because Ca2+ is a major determinant of vascular contraction, we hypothesized that the intracellular free calcium concentration ([Ca2+]i) signaling of vasoconstriction is differentially regulated in systemic microvessels during normal and RUPP in late pregnancy. Pressurized mesenteric microvessels from Norm-Preg and RUPP rats were loaded with fura 2 in preparation for simultaneous measurement of diameter and [Ca2+]i (presented as fura 2 340/380 ratio). Basal [Ca2+]i was lower in RUPP (0.73 +/- 0.03) compared with Norm-Preg rats (0.82 +/- 0.03). Membrane depolarization by 96 mM KCl, phenylephrine (Phe, 10(-5) M), angiotensin II (ANG II, 10(-7) M), or endothelin-1 (ET-1, 10(-7) M) caused an initial peak followed by maintained vasoconstriction and [Ca2+]i. KCl caused similar peak vasoconstriction and [Ca2+]i in Norm-Preg (45.5 +/- 3.3 and 0.89 +/- 0.02%) and RUPP rats (46.3 +/- 2.1 and 0.87 +/- 0.01%). Maximum vasoconstriction to Phe, ANG II, and ET-1 was not significantly different between Norm-Preg (28.6 +/- 4.8, 32.5 +/- 6.3, and 40 +/- 4.6%, respectively) and RUPP rats (27.8 +/- 5.9, 34.4 +/- 4.3, and 38.8 +/- 4.1%, respectively). In contrast, the initial Phe-, ANG II-, and ET-1-induced 340/380 ratio ([Ca2+]i) was reduced in RUPP (0.83 +/- 0.02, 0.82 +/- 0.02, and 0.83 +/- 0.03, respectively) compared with Norm-Preg rats (0.95 +/- 0.04, 0.93 +/- 0.01, and 0.92 +/- 0.02, respectively). Also, the [Ca2+]i-vasoconstriction relationship was similar in KCl-treated but shifted to the left in Phe-, ANG II-, and ET-1-treated microvessels of RUPP compared with Norm-Preg rats. The lower agonist-induced [Ca2+]i signal of vasoconstriction and the leftward shift in the [Ca2+]i-vasoconstriction relationship in microvessels of RUPP compared with Norm-Preg rats suggest activation of [Ca2+]i sensitization pathway(s). The similarity in vasoconstriction in RUPP and Norm-Preg rats suggests that such a [Ca2+]i sensitization pathway(s) may also provide a feedback effect on Ca2+ mobilization/homeostatic mechanisms to protect against excessive vasoconstriction in systemic microvessels during RUPP in late pregnancy.

Adrenomedullin reduces vascular hyperpermeability and improves survival in rat septic shock

OBJECTIVE

Current therapies of sepsis and septic shock require administration of a large volume of fluid to maintain hemodynamic stability. The vasoregulatory peptide adrenomedullin has been shown to prevent the transition to the fatal hypocirculatory septic state by poorly understood mechanisms. We tested the hypothesis that therapeutic administration of adrenomedullin would reduce vascular hyperpermeability, thereby contributing to improved hemodynamics and survival.

DESIGN

Prospective randomized controlled animal study.

SUBJECTS

Male Sprague-Dawley rats (270 g).

INTERVENTIONS

We used 4.8 x 10(3) U/kg of Staphylococcus aureus alpha-toxin, a pore-forming exotoxin, to induce vascular leakage and circulatory shock in rats. The infusion rate was 24 microg/kg per hour. Adrenomedullin was started 1 h after alpha-toxin administration.

MEASUREMENT AND RESULTS

Infusion of alpha-toxin in rats induced cardiocirculatory failure resulting in a 6-h mortality of 53%. alpha-Toxin provoked massive vascular hyperpermeability, which was indicated by an enrichment of Evans blue dye albumin in the tissues of lung, liver, ileum and kidney. Plasma fluid loss led to a significant hemoconcentration. Hemodynamic impairment observed after alpha-toxin infusion was closely correlated to vascular hyperpermeability. Therapeutic administration of 24 microg/kg per hour adrenomedullin reduced 6-h mortality from 53% to 7%. Stabilization of the endothelial barrier by adrenomedullin was indicated by reduced extravasation of albumin and plasma fluid and may have contributed to hemodynamic improvement.

CONCLUSIONS

These data suggest that adrenomedullin-related reduction of vascular hyperpermeability might represent a novel and important mechanism contributing to the beneficial effects of this endogenous vasoregulatory peptide in sepsis and septic shock.