"Rapid actions of the neurosteroid allopregnanolone on ovarian and hypothalamic steroidogenesis: Central and peripheral modulation"

The present study aimed to determine whether an i.c.v. administration of allopregnanolone (ALLO) rapidly modifies the hypothalamic and ovarian 3β-hydroxysteroid dehydrogenase (3β-HSD) enzymatic activity and gene expression in in vivo and ex vivo systems in pro-oestrus (PE) and dioestrus I (DI) rats. Animals were injected with vehicle, ALLO, bicuculline or bicuculline plus ALLO and were then killed. In the in vivo experiment, the hypothalamus, ovaries and serum were extracted and analysed. In the ex vivo experiment, the superior mesenteric ganglion - ovarian nerve plexus - ovary system was extracted and incubated during 120 minutes at 37 ºC. The serum and ovarian compartment fluids were used to determine progesterone by radioimmunoanalysis. In the in vivo experiments, ALLO caused a decrease in hypothalamic and ovarian 3β-HSD enzymatic activity during PE. During DI, ALLO increased hypothalamic and ovarian 3β-HSD activity and gene expression. The ovarian 3β-HSD activity increased in both stages in the ex vivo system; gene expression increased only during DI. ALLO induced an increase in serum progesterone only in D1 and in the ovarian incubation liquids in both stages. All findings were reversed by an injection of bicuculline before ALLO. Ovarian steroidogenic changes could be attributed to signals coming from ganglion neurones, which are affected by the acute central neurosteroid stimulation. The i.c.v. administration of ALLO via the GABAergic system altered 3β-HSD activity and gene expression, modulating the neuroendocrine axis. The present study reveals the action that ALLO exerts on the GABAA receptor in both the central and peripheral nervous system and its relationship with hormonal variations. ALLO is involved in the "fine tuning" of neurosecretory functions as a potent modulator of reproductive processes in female rats.

Estrogen and progesterone dependent expression of visfatin/NAMPT regulates proliferation and apoptosis in mice uterus during estrous cycle

Visfatin is an adipokine which has an endocrine effect on reproductive functions and regulates ovarian steroidogenesis. There is scant information about the expression, regulation, and functions of visfatin in the mammalian uterus. The present study examined expression and localization of visfatin in the mouse uterus at various stages of the natural estrous cycle, effects of estrogen and progesterone on localization and expression of visfatin in the ovariectomised mouse uterus and effect of visfatin inhibition by a specific inhibitor, FK866 on proliferation and apoptosis in the uterus. Western blot analysis of visfatin showed high expression in proestrus and metestrus while it declined in estrus and diestrus. Immulocalization study also showed strong immunostaining in the cells of endometrium, myometrium, luminal and glandular epithelium during proestrus and metestrus that estrus and diestrus. The uterine visfatin expression closely related to the increased estrogen levels in proestrus and suppressed when progesterone rose to a high level in diestrus. The treatment with estrogen to ovariectomised mice up-regulates visfatin, PCNA, and active caspase3 whereas progesterone up-regulates PCNA and down-regulates visfatin and active caspase3 expression in mouse uterus. The co-treatment with estrogen and progesterone up-regulates visfatin and down-regulates PCNA and active caspase3. In vitro study showed endogenous visfatin inhibition by FK866 increased expression of PCNA and BCL2 increased catalase activity while FK866 treatment decreased expression of active caspase3 and BAX with decreased SOD and GPx activity. BrdU labeling showed that inhibition of visfatin modulates the uterine proliferation. This study showed that expression of visfatin protein is steroid dependent in mouse uterus which is involved in the regulation of proliferation and apoptosis via modulating antioxidant system in the uterus of mice during the reproductive cycle.

Ontogeny of clock and KiSS-1 metastasis-suppressor (Kiss1) gene expression in the prepubertal mouse hypothalamus

Kisspeptin is crucial for the generation of the circadian-gated preovulatory gonadotrophin-releasing hormone (GnRH)-LH surge in female rodents, with expression in the anteroventral periventricular nucleus (AVPV) peaking in the late afternoon of pro-oestrus. Given kisspeptin expression is established before puberty, the aim of the present study was to investigate kisspeptin and clock gene rhythms during the neonatal period. Anterior and posterior hypothalami were collected from C57BL/6J mice on Postnatal Days (P) 5, 15 and 25, at six time points across 24h, for analysis of gene expression by reverse transcription-quantitative polymerase chain reaction. Expression of aryl hydrocarbon receptor nuclear translocator-like gene (Bmal1) and nuclear receptor subfamily 1, group D, member 2 (Rev-erbα) in the anterior hypothalamus (containing the suprachiasmatic nucleus) was not rhythmic at P5 or P15, but Bmal1 expression exhibited rhythmicity in P25 females, whereas Rev-erbα expression was rhythmic in P25 males. KiSS-1 metastasis-suppressor (Kiss1) expression did not exhibit time-of-day variation in the anterior (containing the AVPV) or posterior (containing the arcuate nucleus) hypothalami in female and male mice at P5, P15 or P25. The data indicate that the kisspeptin circadian peak in expression observed in the AVPV of pro-oestrous females does not manifest at P5, P15 or P25, likely due to inadequate oestrogenic stimuli, as well as incomplete development of clock gene rhythmicity before puberty.

The participation of the muscarinic receptors in the preoptic-anterior hypothalamic areas in the regulation of ovulation depends on the ovary

BACKGROUND

Muscarinic receptors (mAChRs) of the preoptic and anterior hypothalamus areas (POA-AHA) regulate ovulation in an asymmetric manner during the estrous cycle. The aims of the present study were to analyze the effects of a temporal blockade of mAChRs on either side of the POA-AHA performed in diestrus-2 rats on ovulation, the levels of estradiol, follicle stimulating hormone (FSH) and luteinizing hormone (LH) and the mechanisms involved in changes in ovulation.

METHODS

Cyclic rats on diestrus-2 day were anesthetized and randomly assigned to the following groups: 1) microinjection of 1 μl of saline or atropine solution (62.5 ng) in the left or right POA-AHA; 2) removal (unilateral ovariectomty, ULO) of the left (L-ULO) or right (R-ULO) ovary, and 3) rats microinjected with atropine into the left or right POA-AHA plus L-ULO or R-ULO. The ovulation rate and the number of ova shed were measured during the predicted estrus, as well as the levels of estradiol, FSH and LH during the predicted proestrus and the effects of injecting synthetic LH-releasing hormone (LHRH) or estradiol benzoate (EB).

RESULTS

Atropine in the left POA-AHA decreased both the ovulation rate and estradiol and LH levels on the afternoon of proestrus, also LHRH or EB injection restored ovulation. L- or R-ULO resulted in a lower ovulation rate and smaller number of ova shed, and only injection of LHRH restored ovulation. EB injection at diestrus-2 restored ovulation in animals with L-ULO only. The levels of estradiol, FSH and LH in rats with L-ULO were higher than in animals with unilateral laparotomy. In the group microinjected with atropine in the left POA-AHA, ovulation was similar to that in ULO rats. In contrast, atropine in the right POA-AHA of ULO rats blocked ovulation, an action that was restored by either LHRH or EB injection.

CONCLUSIONS

These results indicated that the removal of a single ovary at noon on diestrus-2 day perturbed the neuronal pathways regulating LH secretion, which was mediated by the muscarinic system connecting the right POA-AHA and the ovaries.

High-fat diet with stress impaired islets' insulin secretion by reducing plasma estradiol and pancreatic GLUT2 protein levels in rats' proestrus phase

This study was conducted to determine whether two estrus phases (proestrus and diestrus) in female rats may influence the metabolic response to a high-fat diet and/or stress, focusing on pancreatic insulin secretion and content. Animals were divided into high-fat and normal diet groups, then each group was subdivided into stress and non-stress groups, and finally, each one of these was divided into proestrus and diestrus subgroups. At the end of high-fat diet treatment, foot-shock stress was applied to the animals. Then, blood samples were taken to measure plasma factors. Finally, the pancreas was removed for determination of glucose transporter 2 (GLUT2) protein levels and assessment of insulin content and secretion of the isolated islets. In the normal and high-fat diet groups, stress increased plasma corticosterone concentration in both phases. In both study phases, high-fat diet consumption decreased estradiol and increased leptin plasma levels. In the high-fat diet group in response to high glucose concentration, a reduction in insulin secretion was observed in the proestrus phase compared with the same phase in the normal diet group in the presence and absence of stress. Also, high-fat diet decreased the insulin content of islets in the proestrus phase compared with the normal diet. High-fat diet and/or stress caused a reduction in islet GLUT2 protein levels in both phases. In conclusion, it seems possible that high-fat diet alone or combined with foot-shock, predispose female rats to impaired insulin secretion, at least in part, by interfering with estradiol levels in the proestrus phase and decreasing pancreatic GLUT2 protein levels.

Unilaterally blocking the muscarinic receptors in the suprachiasmatic nucleus in proestrus rats prevents pre-ovulatory LH secretion and ovulation

BACKGROUND

The suprachiasmatic nucleus (SCN) and the cholinergic system of various regions of the hypothalamus participate in the regulation of gonadotropin-releasing hormone (GnRH) and gonadotropin secretion, which are necessary for the occurrence of ovulation. In the present study, our goal was to analyse the effects of unilaterally blocking the muscarinic receptors in the SCN on ovulation and steroid secretion.

METHODS

Cyclic rats were randomly allotted to one of the experimental groups. Groups of 8-14 rats were anaesthetized and microinjected with 0.3 μl of saline or a solution of atropine (62.5 ng in 0.3 μl of saline) into the left or right SCN at 09.00 or 19.00 h during diestrus-1 or on the proestrus day. The rats were euthanized on the predicted day of oestrus, and evaluated ovulation and levels of progesterone and oestradiol. Other groups of 10 rats were microinjected with atropine into the left or right SCNs at 09.00 h on the proestrus day, were euthanized eight h later, and luteinizing hormone (LH) was measured.

RESULTS

At 09.00 or 19.00 h during diestrus-1, atropine microinjections into the SCNs on either side did not modify ovulation. The atropine microinjections performed at 09.00 h of proestrus into either side of the SCN blocked ovulation (right SCN: 1/9 ovulated vs. 9/10 in the saline group; left SCN: 8/14 ovulated vs. 10/10 in the saline group). The LH levels at 17.00 h in the rats that were microinjected with atropine at 09.00 h of proestrus were lower than those of the controls. In the non-ovulating atropine-treated rats, the injection of synthetic LH-releasing hormone (LHRH) restored ovulation. Atropine treatment at 19.00 h of proestrus on either side of the SCN did not modify ovulation, while the progesterone and oestradiol levels were lower.

CONCLUSION

Based on the present results, we suggest that the cholinergic neural information arriving on either side of the SCN is necessary for the pre-ovulatory secretion of LH to induce ovulation. Additionally, the regulation of progesterone and oestradiol secretion by the cholinergic innervation of the SCN varies with the time of day, the day of the cycle, and the affected SCN.

Molecular Plasticity of Male and Female Murine Gonadotropes Revealed by mRNA Sequencing

Gonadotropes in the anterior pituitary gland are of particular importance within the hypothalamic-pituitary-gonadal axis because they provide a means of communication and thus a functional link between the brain and the gonads. Recent results indicate that female gonadotropes may be organized in the form of a network that shows plasticity and adapts to the altered endocrine conditions of different physiological states. However, little is known about functional changes on the molecular level within gonadotropes during these different conditions. In this study we capitalize on a binary genetic strategy in order to fluorescently label murine gonadotrope cells. Using this mouse model allows to produce an enriched gonadotrope population using fluorescence activated cell sorting to perform mRNA sequencing. By using this strategy, we analyze and compare the expression profile of murine gonadotropes in different genders and developmental and hormonal stages. We find that gonadotropes taken from juvenile males and females, from cycling females at diestrus and at proestrus, from lactating females, and from adult males each have unique gene expression patterns with approximately 100 to approximately 500 genes expressed only in one particular stage. We also demonstrate extensive gene-expression profile changes with up to approximately 2200 differentially expressed genes when comparing female and male development, juveniles and adults, and cycling females. Differentially expressed genes were significantly enriched in the GnRH signaling, calcium signaling, and MAPK signaling pathways by Kyoto Encyclopedia of Genes and Genomes analysis. Our data provide an unprecedented molecular view of the primary gonadotropes and reveal a high degree of molecular plasticity within the gonadotrope population.

EP24.15 as a Potential Regulator of Kisspeptin Within the Neuroendocrine Hypothalamus

The neuropeptide kisspeptin (Kiss1) is integral to the advent of puberty and the generation of cyclical LH surges. Although many complex actions of Kiss1 are known, the mechanisms governing the processing/regulation of this peptide have not been unveiled. The metallo enzyme, endopeptidase 24.15 (thimet oligopeptidase), has been demonstrated to play a key role in the processing and thus the duration of action of the reproductive neuropeptide, GnRH, which signals downstream of Kiss1. Initial in silico modeling implied that Kiss1 could also be a putative substrate for EP24.15. Coincubation of Kiss1 and EP24.15 demonstrated multiple cleavages of the peptide predominantly between Arg29-Gly30 and Ser47-Phe48 (corresponding to Ser5-Phe6 in Kiss-10; Kiss-10 as a substrate had an additional cleavage between Phe6-Gly7) as determined by mass spectrometry. Vmax for the reaction was 2.37±0.09 pmol/min · ng with a Km of 19.68 ± 2.53μM, which is comparable with other known substrates of EP24.15. EP24.15 immunoreactivity, as previously demonstrated, is distributed in cell bodies, nuclei, and processes throughout the hypothalamus. Kiss1 immunoreactivity is localized primarily to cell bodies and fibers within the mediobasal and anteroventral-periventricular hypothalamus. Double-label immunohistochemistry indicated coexpression of EP24.15 and Kiss1, implicating that the regulation of Kiss1 by EP24.15 could occur in vivo. Further studies will be directed at determining the precise temporal sequence of EP24.15 effects on Kiss1 as it relates to the control of reproductive hormone secretion and treatment of fertility issues.

Hepatic and Whole-Body Insulin Metabolism during Proestrus and Estrus in Mongrel Dogs

Insulin resistance occurs during various stages of the estrus cycle in dogs. To quantify the effects of proestrus-estrus (PE) and determine whether PE affects liver insulin sensitivity, 11 female mongrel dogs were implanted with sampling and intraportal infusion catheters. Five of the dogs (PE group) entered proestrus after surgery; those remaining in anestrus were controls. The dogs were fasted overnight, [3-(3)H]glucose and somatostatin were infused through peripheral veins, and glucagon was infused intraportally. Insulin was infused intraportally, with the rate adjusted to maintain arterial plasma glucose at basal levels (PE, 294±25 μU/kg/min; control, 223±21 μU/kg/min). Subsequently the insulin infusion rate was increased by 0.2 mU/kg/min for 120 min (P1) and then to 1.5 mU/kg/min for the last 120 min (P2); glucose was infused peripherally as needed to maintain euglycemia. Insulin concentrations did not differ between groups at any time; they increased 3 μU/mL over baseline during P1 and to 3 times baseline during P2. The glucose infusion rate in PE dogs during P2 was 63% of that in control dogs. Net hepatic glucose output and the endogenous glucose production rate declined 40% to 50% from baseline in both groups during P1; during P2, both groups exhibited a low rate of net hepatic glucose uptake with full suppression of endogenous glucose production. The glucose disappearance rate during P1 and P2 was 35% greater in control than PE dogs. Therefore, PE in canines is associated with loss of nonhepatic (primarily muscle) but not hepatic insulin sensitivity.

Evidence for a Putative Circadian Kiss-Clock in the Hypothalamic AVPV in Female Mice

The kisspeptin (Kp) neurons in the anteroventral periventricular nucleus (AVPV) are essential for the preovulatory LH surge, which is gated by circulating estradiol (E2) and the time of day. We investigated whether AVPV Kp neurons in intact female mice may be the site in which both E2 and daily signals are integrated and whether these neurons may host a circadian oscillator involved in the timed LH surge. In the afternoon of proestrous day, Kp immunoreactivity displayed a marked and transient decrease 2 hours before the LH surge. In contrast, Kp content was stable throughout the day of diestrus, when LH levels are constantly low. AVPV Kp neurons expressed the clock protein period 1 (PER1) with a daily rhythm that is phase delayed compared with the PER1 rhythm measured in the main clock of the suprachiasmatic nuclei (SCN). PER1 rhythm in the AVPV, but not in the SCN, exhibited a significant phase delay of 2.8 hours in diestrus as compared with proestrus. Isolated Kp-expressing AVPV explants from PER2::LUCIFERASE mice displayed sustained circadian oscillations of bioluminescence with a circadian period (23.2 h) significantly shorter than that of SCN explants (24.5 h). Furthermore, in AVPV explants incubated with E2 (10 nM to 1 μM), the circadian period was lengthened by 1 hour, whereas the SCN clock remained unaltered. In conclusion, these findings indicate that AVPV Kp neurons display an E2-dependent daily rhythm, which may possibly be driven by an intrinsic circadian clock acting in combination with the SCN timing signal.

Female mice with deletion of Type One 5α-reductase have reduced reproductive responding during proestrus and after hormone-priming

The capacity to form progesterone (P₄)'s 5α-reduced metabolite, 5α-pregnan-3α-ol-20-one (3α,5α-THP; a.k.a. allopregnanolone), in the brain may be related to facilitation of lordosis among estrogen-primed (E₂) mice. We investigated this idea further by comparing effects of endogenous and exogenous progestogens in mice that are deficient in the Type One 5α-reductase enzyme (5α-reductase knockout mice; 5α-RKO), and their wildtype counterparts for sexual behavior. Comparisons were made following administration of progestogens that are expected to increase 3α,5α-THP or not. Sexual receptivity of 5α-RKO mice and their wildtype counterparts was examined when mice were naturally-cycling (Experiment 1); ovariectomized (OVX), E₂-primed (10 μg, subcutaneous; SC) and administered P₄ (0, 125, 250, or 500 μg SC; Experiment 2); and OVX, E₂-primed and administered P₄, medroxyprogesterone acetate (MPA, 4 mg/kg, SC, which does not convert to 3α,5α-THP) or 3α,5α-THP (4 mg/kg, SC; Experiment 3). The percentage of mounts that elicited lordosis (lordosis quotient) or aggression/rejection behavior (aggression quotient), as well as the quality of lordosis (lordosis rating), was scored. Wildtype, but not 5α-RKO, mice in behavioral estrus demonstrated significantly greater lordosis quotients and lordosis ratings, but similar aggression quotients, compared to their diestrous counterparts. Among OVX and E₂-primed mice, P₄ facilitated lordosis of wildtype, but not 5α-RKO, mice. MPA neither facilitated lordosis of wildtype, nor 5α-RKO mice. 3α,5α-THP administered to wildtype or 5α-RKO mice increased lordosis quotients and lordosis ratings and decreased aggression quotients. 3α,5α-THP levels in the midbrain, one brain region important for sexual behavior, were increased during behavioral estrus, with P4 administered to WT, but not 5α-RKO mice, and 3α,5α-THP administered to WT and 5α-RKO mice. MPA did not increase 3α,5α-THP. Thus, deletion of Type One 5α-reductase among female mice may attenuate reproductive responding during the estrous cycle and after hormone-priming.

Estrogens downregulate urocortin 2 expression in rat uterus

Urocortin 2 (Ucn2) is a member of the corticotropin-releasing factor peptide family and is expressed by various tissues, including reproductive tissues such as the uterus, ovary, and placenta. However, the regulatory mechanisms of Ucn2 expression and the physiological significance of Ucn2 in these tissues remain unclear. We previously showed that passive immunization of immature female rats by i.p. injection of anti-Ucn2 IgG induces earlier onset of puberty. Therefore, this study was designed to clarify the site and regulatory mechanisms of Ucn2 expression in the uterus. Expression levels of Ucn2 mRNA in the uterus were higher in immature (2- and 4-week-old) and aged (17-month-old) rats than in mature (9-week-old) rats in the proestrus phase. In 9-week-old rats, mRNA expression levels and contents in the uterus were lower in the proestrus phase than in the diestrus phase, while plasma Ucn2 concentrations did not differ between the two phases. Ucn2-like immunoreactivitiy was detected in the endometrial gland epithelial cells of the uterus. S.c. injection of estradiol benzoate or an estrogen receptor α (ERα) agonist significantly reduced mRNA expression levels and contents of Ucn2 in the uterus when compared with vehicle-injected ovariectomized rats. By contrast, estradiol benzoate increased Ucn2 mRNA expression levels in the lung. Thus, estrogens downregulate Ucn2 expression in the uterus in a tissue-specific manner, and Ucn2 may play a role in the regulatory mechanisms of maturation of the uterus through ERα and estrous cycle.

Free fatty acids induce Lhb mRNA but suppress Fshb mRNA in pituitary LβT2 gonadotropes and diet-induced obesity reduces FSH levels in male mice and disrupts the proestrous LH/FSH surge in female mice

Female obesity is associated with insulin resistance, hyperandrogenemia, and reproductive dysfunction. We hypothesized that elevated free fatty acids (FFAs) might directly modulate pituitary gonadotropin production. FFAs caused a time- and dose-dependent increase in phosphorylation of the MAPKs p38MAPK, c-Jun N-terminal kinase (JNK)-1/2, and ERK1/2 in LβT2 gonadotrope cells. Furthermore, FFAs up-regulated Lhb mRNA expression acutely, an effect that was blocked by JNK inhibition, but suppressed Fshb mRNA expression, an effect that was independent of MAPK signaling. FFAs enhanced the activation of the MAPKs in the presence of GnRH, although the cotreatment did not alter Lhb induction but did eliminate the GnRH induction of Fshb. FFAs also suppressed activin-induced Fshb expression. Knockdown experiments showed that the FFA effect on the inflammatory kinases p38MAPK and JNK and on Lhb, but not Fshb, mRNA expression is mediated via toll-like receptor-2 and toll-like receptor-4 and was mimicked by lipopolysaccharide stimulation. In vivo, male C57BL/6 mice on a high-fat diet showed reduced FSH levels consistent with the suppression of Fshb seen in vitro. Histological analysis of the testes showed an increased number of abnormal seminiferous tubules. Female mice on a high-fat diet lacked the expected proestrus LH and FSH surge and exhibited an increase in the number of days at estrus and a reduced number of days at proestrus, and ovaries had significantly fewer corpora lutea. Taken together, our findings suggest that lipid excess can lead to reproductive defects in both male and female mice.

Ovarian hormones influence corticotropin releasing factor receptor colocalization with delta opioid receptors in CA1 pyramidal cell dendrites

Stress interacts with addictive processes to increase drug use, drug seeking, and relapse. The hippocampal formation (HF) is an important site at which stress circuits and endogenous opioid systems intersect and likely plays a critical role in the interaction between stress and drug addiction. Our prior studies demonstrate that the stress-related neuropeptide corticotropin-releasing factor (CRF) and the delta-opioid receptor (DOR) colocalize in interneuron populations in the hilus of the dentate gyrus and stratum oriens of CA1 and CA3. While independent ultrastructural studies of DORs and CRF receptors suggest that each receptor is found in CA1 pyramidal cell dendrites and dendritic spines, whether DORs and CRF receptors colocalize in CA1 neuronal profiles has not been investigated. Here, hippocampal sections of adult male and proestrus female Sprague-Dawley rats were processed for dual label pre-embedding immunoelectron microscopy using well-characterized antisera directed against the DOR for immunoperoxidase and against the CRF receptor for immunogold. DOR-immunoreactivity (-ir) was found presynaptically in axons and axon terminals as well as postsynaptically in somata, dendrites and dendritic spines in stratum radiatum of CA1. In contrast, CRF receptor-ir was predominantly found postsynaptically in CA1 somata, dendrites, and dendritic spines. CRF receptor-ir frequently was observed in DOR-labeled dendritic profiles and primarily was found in the cytoplasm rather than at or near the plasma membrane. Quantitative analysis of CRF receptor-ir colocalization with DOR-ir in pyramidal cell dendrites revealed that proestrus females and males show comparable levels of CRF receptor-ir per dendrite and similar cytoplasmic density of CRF receptor-ir. In contrast, proestrus females display an increased number of dual-labeled dendritic profiles and an increased membrane density of CRF receptor-ir in comparison to males. We further examined the functional consequences of CRF receptor-ir colocalization with DOR-ir in the same neuron using the hormone responsive neuronal cell line NG108-15, which endogenously expresses DORs, and assayed intracellular cAMP production in response to CRF receptor and DOR agonists. Results demonstrated that short-term application of DOR agonist SNC80 inhibited CRF-induced cAMP accumulation in NG108-15 cells transfected with the CRF receptor. These studies provide new insights on opioid-stress system interaction in the hippocampus of both males and females and establish potential mechanisms through which DOR activation may influence CRF receptor activity.

Gene expression profiles of intracellular and membrane progesterone receptor isoforms in the mediobasal hypothalamus during pro-oestrus

Progesterone action is mediated by its binding to specific receptors. Two progesterone receptor (PR) isoforms (PRA and PRB), three membrane progesterone receptor (mPR) subtypes (mPRalpha, mPRbeta and mPRgamma) and at least one progesterone membrane-binding protein [PR membrane component 1 (PRmc1)] have been identified in reproductive tissues and brain of various species. In the present study, we examined gene expression patterns for PR isoforms, mPR subtypes and PRmc1 in the rat mediobasal hypothalamus (MBH) during pro-oestrus. The mRNA level for each receptor subtype was quantified by a real-time reverse transcriptase-polymerase chain reaction (RT-PCR) at the time points: 13.00 h on dioestrous day 2; 09.00, 13.00, 17.00 and 22.00 h on pro-oestrus; and 13.00 h on oestrus. For PR, one primer set amplified PRA+PRB, whereas a second primer set amplified PRB. As expected, PRA+PRB mRNA expression was greater than PRB in MBH tissue. PRB mRNA levels increased throughout the day on pro-oestrus, with the highest levels being observed at 17.00 h. PRB mRNA levels in the MBH were increased by 2.4- and 3.0-fold at 13.00 and 17.00 h, respectively, on pro-oestrus compared to 13.00 h on dioestrous day 2. There were differential mRNA expression levels for mPRs and PRmc1 in the MBH, with the highest expression for PRmc1 and the lowest for mPRgamma. The mPRalpha mRNA contents at 13.00 and 17.00 h on pro-oestrus were increased by 1.5-fold compared to that at 13.00 h on dioestrous day 2. The mPRbeta mRNA levels at 13.00 and 17.00 h on pro-oestrus were 2.5- and 2.4-fold higher compared to that at 13.00 h on dioestrous day 2, respectively. PRA+PRB, mPRgamma and PRmc1 mRNA levels did not vary on pro-oestrus. These findings suggest that the higher expression of PRB, mPRalpha and mPRbeta in the MBH on pro-oestrous afternoon may influence both genomic and nongenomic mechanisms of progesterone action during the critical pre-ovulatory period.

Norepinephrine suppresses gonadotropin-releasing hormone neuron excitability in the adult mouse

Norepinephrine (NE) is considered to exert an important modulatory influence upon the activity of GnRH neurons. In the present study, we used a transgenic GnRH-green fluorescent protein mouse model to examine the effects of NE on the electrical excitability of GnRH neurons in male and female mice. Gramicidin-perforated patch recordings demonstrated that NE (10-100 mum) exerted a robust membrane hyperpolarization, with associated suppression of firing, in more than 85% of male prepubertal and adult GnRH neurons (n = 25). The same hyperpolarizing action was observed in female GnRH neurons from diestrous (91%, n = 11), proestrous (50%, n = 14), estrous (77%, n = 13), and ovariectomized (82%, n = 11) mice. A subpopulation (<10%) of silent GnRH neurons in all groups responded to NE with hyperpolarization followed by the initiation of firing upon NE washout. The hyperpolarizing actions of NE were mimicked by alpha1-adrenergic (phenylephrine) and beta-adrenergic (isoproterenol) receptor agonists, but alpha2 receptor activation (guanabenz) had no effect. Approximately 75% of the NE-evoked hyperpolarization was blocked by the alpha1 receptor antagonist prazosin, and 75% of GnRH neurons responded to both phenylephrine and isoproterenol. These findings indicate that NE acts through both alpha1- and beta-adrenergic receptors located on the soma/dendrites of GnRH neurons to directly suppress their excitability throughout the estrous cycle and after ovariectomy. These data force a reanalysis of existing models explaining the effects of NE on gonadotropin secretion.

Effects of acute stress on the day of proestrus on sexual behavior and ovulation in female rats: Participation of the angiotensinergic system

Physical or emotional stress can affect the female reproductive physiology and angiotensin II (Ang II) is a hormone that participates in the stress response and also in the control of reproductive hormones. The present study aimed at evaluating the effects of acute stress in the morning and afternoon of proestrus on sexual behavior and ovulation and the participation of Ang II in the stress-induced effects. Female rats with regular estrous cycles were used. Several different stress protocols were tested in the morning and in the afternoon of proestrus: restraint stress 10 min; restraint stress 1 h and ether stress, respectively. The participation of Ang II was evaluated by injecting Ang II receptor antagonists (losartan and PD123319) 15 min before stress. The lordosis quotient was recorded and the number of oocytes was counted. Plasma levels of luteinizing hormone, progesterone, prolactin and corticosterone were measured. All types of stress in the morning of proestrus induced a reduction in the number of oocytes. Restraint stress (1 h) in the afternoon of proestrus induced a significant reduction in the lordosis quotient. Peripheral and central losartan, but not PD123319, injections partly reverted the effects of stress on ovulation in the morning of proestrus. Acute stress in the morning of proestrus also reduced luteinizing hormone, progesterone and prolactin surges later on the same day. In conclusion, acute stress on the day of proestrus can affect female reproductive physiology. Moreover, the angiotensinergic system, through AT(1) receptors, participates in the effects of acute stress in the morning of proestrus.

AKR1B7 (mouse vas deferens protein) is dispensable for mouse development and reproductive success

AKR1B7 (aldo-keto reductase family 1, member 7; also known as mouse vas deferens protein) is a member of the AKR superfamily, and has been suggested to play a role in detoxifying processes on account of its preferred substrates, 4-hydroxynonenal and isocaproaldehyde. High levels of protein expression were found in the vas deferens and the adrenal gland, where sustained expression is dependent on androgen or ACTH respectively. Recently, a remarkable induction of AKR1B7 expression has been reported in the ovary following exogenous injections of LH. In the present study, we confirm this regulation physiologically during the estrous cycle, observing Akr1b7 expression to be restricted to the theca and stromal cells of the proestrus ovary. To further investigate the role of this detoxifying enzyme in both male and female reproduction, we generated knockout mice deficient in AKR1B7. Although AKR1B7 expression in the vas deferens is considerable and tightly regulated in the ovary of wild-type animals, homozygous mutant animals were found to be viable and no reproductive phenotype was observed. Ovarian follicle maturation and spermatozoa parameters remained normal in the absence of this protein. The determination of serum progesterone revealed an increase in hormone concentration in metestrus, while progesterone was found to be decreased in the estrus phase of the cycle in knockout females.

Luteinizing hormone beta promoter stimulation by adenylyl cyclase and cooperation with gonadotropin-releasing hormone 1 in transgenic mice and LBetaT2 Cells

Rat luteinizing hormone beta (Lhb) gene transcription is stimulated by hypothalamic gonadotropin-releasing hormone 1 (GnRH1), and this response may be modulated by other signaling pathways such as cAMP. Here we characterize the ability of cAMP, alone or with GnRH1, to stimulate Lhb gene transcription in mouse pituitary and clonal gonadotroph cells. Both cAMP and pituitary adenylyl cyclase-activating peptide increase GnRH1 stimulation of luciferase activity in pituitaries of mice expressing the rat Lhb-luciferase transgene, suggesting cAMP and GnRH1 pathways interact in vivo. cAMP stimulation of the Lhb-luciferase transgene was similar between females in metestrus and proestrus, but GnRH1 stimulation was greater at proestrus. Additive effects with combined treatments were observed at metestrus and proestrus. Elevated intracellular cAMP stimulated Lhb promoter activity in LbetaT2 clonal gonadotroph cells, alone and with GnRH1. In LbetaT2 cells, cAMP stimulation of the Lhb promoter was eliminated by inhibition of protein kinase A (PKA); GnRH1 stimulation was partially suppressed by either PKA or protein kinase C inhibitors. Only the proximal GnRH1-responsive region of the promoter was required for cAMP stimulation, and mutation of the 3' NR5A1 site diminished the response. Regulation of primary mRNA transcripts from the endogenous Lhb gene by cAMP and GnRH1 correlated with results from the Lhb-luciferase transgene or transfected promoter. Occupancy of the endogenous promoter by EGR1 was increased by GnRH1 with or without forskolin, but forskolin alone had little effect. Thus, cAMP stimulation of Lhb promoter activity, and enhancement of GnRH1 stimulation, occurs in multiple physiological states independent of steroid status, via a PKA-dependent mechanism.

Prolactin secretory surge during estrus coincides with increased dopamine activity in the hypothalamus and preoptic area and is not altered by ovariectomy on proestrus

Prolactin (PRL) secretory surges have been reported on the afternoons of both proestrus and estrous in cycling rats. As neuroendocrine regulation of estrous PRL surge is poorly understood, the present study aimed to investigate the involvement of hypothalamic dopamine and serotonin as well as of plasma ovarian steroids in this hormonal surge generation. For that, we determined the concentrations of dopamine, serotonin and their respective metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindole-3-acetic acid (5-HIAA) in the mediobasal hypothalamus (MBH) and medial preoptic area (MPOA) throughout the day of estrus and correlated them with plasma PRL levels. In a second study, we evaluated the effect of ovariectomy on the morning of proestrus on PRL surges of both proestrus and estrus. Dopamine turnover, as determined by DOPAC/dopamine ratio, increased in both the MBH and MPOA coinciding with the afternoon PRL surge on estrus. In contrast, both the concentration and turnover (5-HIAA/serotonin) of serotonin within these areas were unaltered during estrus. In addition, ovariectomy reduced plasma estradiol and progesterone levels but did not alter the PRL surges on proestrus and estrus. Considering that dopamine is the main inhibitor of PRL release and that PRL auto-regulates its secretion through a short-loop feedback mechanism, our present results suggest that PRL may suppress its own secretion during the estrus surge through the activation of the dopaminergic neurons in the MBH and MPOA. In addition, the PRL surge on estrus seems do not depend on either the activity of hypothalamic serotonin or the increased secretion of ovarian steroids on proestrus.

Hormonal profile and reproductive performance in lactation deficient (OFA hr/hr) and normal (Sprague–Dawley) female rats

Lactation deficiency may have important consequences on infant health, particularly in populations of low socioeconomic status. The OFAhr/hr(OFA) strain of rats, derived from Sprague–Dawley (SD) rats, has deficient lactation and is a good model of lactation failure. We examined the reproductive performance and hormonal profiles in OFA and SD strains to determine the cause(s) of the lactation failure of the OFA strain. We measured hormonal (PRL, GH, gonadotropins, oxytocin, and progesterone) levels by RIA in cycling, pregnant, and lactating rats and in response to suckling. Dopaminergic metabolism was assessed by determination of mediobasal hypothalamic dopamine and dihydroxyphenylacetic acid (DOPAC) concentrations by HPLC and tyrosine hydroxylase expression by immunocytochemistry and western blot. OFA rats have normal fertility but 50% of the litters die of malnutrition on early lactation; only 6% of the mothers show normal lactation. The OFA rats showed lower circulating PRL during lactation, increased hypothalamic dopamine and DOPAC, and impaired milk ejection with decreased PRL and oxytocin response to suckling. Before parturition, PRL release and lactogenesis were normal, but dopaminergic metabolism was altered, suggesting activation of the dopaminergic system in OFA but not in SD rats. The number of arcuate and periventricular neurons expressing tyrosine hydroxylase was higher in SD rats, but hypothalamic expression of TH was higher in OFA rats at the end of pregnancy and early lactation. These results suggest that the OFA rats have impaired PRL release linked with an augmented dopaminergic tone which could be partially responsible for the lactational failure.

Impact of proestrous milieu on expression of orexin receptors and prepro-orexin in rat hypothalamus and hypophysis: actions of Cetrorelix and Nembutal

Orexins and their receptors OX1 and OX2 regulate energy balance and the sleep-wake cycle. We studied the expression of prepro-orexin (PPO), OX1, and OX2 in brain and pituitary under the influence of the hormonal status in adult rats. Primarily, PPO, OX1, and OX2 expression was determined in Sprague-Dawley female cycling rats during proestrus and in males. Animals were killed at 2-h intervals. Anterior (AH) and mediobasal (MBH) hypothalamus, anterior pituitary (P), and frontoparietal cortex (CC) were homogenized in TRIzol, and mRNAs were obtained for screening of PPO, OX1, OX2 expression by semiquantitative RT-PCR. Main findings were confirmed and extended to all days of the cycle by quantitative real-time RT-PCR. Hormones and food consumption were determined. Finally, OX1, OX2, and PPO were measured by real-time RT-PCR in tissues collected at 1900 of proestrus after treatments at 1400 with ovulation-blocking agents Cetrorelix or pentobarbital. OX1 and OX2 expression increased at least threefold in AH, MBH, and P, but not in CC, between 1700 and 2300 of proestrus, without variations in estrus, diestrus, or in males. PPO in AH and MBH showed a fourfold or higher increase only during proestrus afternoon. Cetrorelix or pentobarbital prevented increases of OX1 and OX2 only in the pituitary and blunted gonadotropin surges, but left OX1, OX2, and PPO brain expression unchanged. Reproduction, energy balance, and sleep-wake cycle are integrated. Here, we demonstrate that, in the physiological neuroendocrine condition leading to ovulation, information to the orexinergic system acts in hypothalamus and pituitary by different mechanisms.

Fluctuation of synapse density in the arcuate nucleus during the estrous cycle

The hypothalamic arcuate nucleus integrates different hormonal and neural signals to control neuroendocrine events, feeding, energy balance and reproduction. Previous studies have shown that in adult female rats the arcuate nucleus undergoes a cyclic fluctuation in the number of axo-somatic synapses during the estrous cycle, in parallel to the variation of ovarian hormone levels in plasma. In the present study we have used an unbiased stereological analysis in conjunction with postembedding immunocytochemistry to assess whether the synaptic remodeling during the estrous cycle in rats is specific for certain types of synapses. Our findings indicate that there is a significant decrease in the number of GABAergic axo-somatic synapses on proestrus afternoon and estrus day compared with other days of the estrous cycle. This decrease in GABAergic synapses is accompanied by an increase in the number of dendritic spine synapses. The synaptic density appears to cycle back to proestrus morning values on metestrus day. In contrast, the number of synapses on dendritic shafts does not change during the cycle. These results indicate that a rapid and selective synaptic turnover of arcuate synapses occurs in physiological circumstances.

Neuromedin s as novel putative regulator of luteinizing hormone secretion

Neuromedin S (NMS), a 36 amino acid peptide structurally related to neuromedin U, was recently identified in rat brain as ligand for the G protein-coupled receptor FM4/TGR-1, also termed neuromedin U receptor type-2 (NMU2R). Central expression of NMS appears restricted to the suprachiasmatic nucleus, and NMS has been involved in the regulation of dark-light rhythms and suppression of food intake. Reproduction is known to be tightly regulated by metabolic and photoperiodic cues. Yet the potential contribution of NMS to the control of reproductive axis remains unexplored. We report herein analyses of hypothalamic expression of NMS and NMU2R genes, as well as LH responses to NMS, in different developmental and functional states of the female rat. Expression of NMS and NMU2R genes was detected at the hypothalamus along postnatal development, with significant fluctuations of their relative levels (maximum at prepubertal stage and adulthood). In adult females, hypothalamic expression of NMS (which was confined to suprachiasmatic nucleus) and NMU2R significantly varied during the estrous cycle (maximum at proestrus) and was lowered after ovariectomy and enhanced after progesterone supplementation. Central administration of NMS evoked modest LH secretory responses in pubertal and cyclic females at diestrus, whereas exaggerated LH secretory bursts were elicited by NMS at estrus and after short-term fasting. Conversely, NMS significantly decreased elevated LH concentrations of ovariectomized rats. In summary, we provide herein novel evidence for the ability of NMS to modulate LH secretion in the female rat. Moreover, hypothalamic expression of NMS and NMU2R genes appeared dependent on the functional state of the female reproductive axis. Our data are the first to disclose the potential implication of NMS in the regulation of gonadotropic axis, a function that may contribute to the integration of circadian rhythms, energy balance, and reproduction.

Non-neuronal acetylcholine and choline acetyltransferase in oviductal epithelial cells of cyclic and pregnant pigs

Certain female reproductive tissues are known to express the non-neuronal cholinergic system. Using different experimental approaches, we tested the hypothesis that acetylcholine (ACh) in the porcine oviduct may also be derived from non-neuronal structures. Immunohistochemistry was performed to detect acetylcholine synthesizing enzyme choline acetyltransferase (ChAT) in different segments of the oviduct of cyclic and pregnant sows. Immunohistochemical experiments revealed strong immunoexpression of ChAT in the entire oviductal epithelium at metoestrus. Thereby, a particular pronounced staining was found in the supranuclear region of almost all epithelial cells. Immunostaining of ChAT decreased markedly during dioestrus and prooestrus stages, respectively. At prooestrus, ChAT immunoreactivity was confined to ciliated cells. Furthermore, we found elevated level of staining intensity of ChAT in the pregnant oviduct at day 13. Using the same ChAT antibody for Western blot analyses, we detected immunoreactive bands of MW 69,000 and 46,000 mainly in ampulla, while MW 58,000 and 30,000 forms were present mainly in infundibulum and isthmus. Furthermore ACh was detected by HPLC and fluorimetric methods in oviductal epithelium. In conclusion, we show expression of ChAT in oviductal epithelial cells at different stages of the oestrus cycle and pregnancy, indicating that these cells can synthesize ACh in a cycle-dependent manner. These results suggest as yet unexplored roles of epithelial ACh in the oviduct.

Effect of alpha-melanotropin hormone on serum levels of luteinizing hormone and progesterone in experimental rat autoimmune oophoritis

We studied the effect of alpha-melanotropin hormone (alpha-MSH) on experimental autoimmune oophoritis (EAO), an inflammatory process induced in female rats. During proestrus, serum levels of LH and progesterone in rats with EAO were higher than those of control rats. However, administration of alpha-MSH to these rats decreased the levels of LH. Similarly, in the following diestrus, rats with EAO had high levels of LH but treatment with alpha-MSH decreased the levels to diestrus 2 control values. Treatment with alpha-MSH also reduced the LH levels of control rats in diestrus 2 compared to untreated controls. However, alpha-MSH treatment had no effect on progesterone levels of either control or rats with EAO. Thus, although alpha-MSH induced notable changes in levels of LH, this decrease was unable to block the illness.

Spontaneous appearance of uterine tumors in vehicle and 3-methylcholanthrene-treated Wistar rats

During the conduct of a study designed to determine the effect of 3-methylcholanthrene (3-MC), a synthetic polycyclic aromatic hydrocarbon (PAH) that acts through the aryl hydrocarbon receptor (AhR), on uterine contractility in Wistar rats, uterine tumors were identified in both vehicle and 3-MC-treated animals. The objective of the current study was to describe the histological characteristics of these tumors. Sexually mature female rats (110 days old) were treated with 70 micro mol/kg 3-MC or vehicle (olive oil) for 4 days and euthanized by exsanguination. At necropsy uterine tumors were unexpected findings in two vehicle and four 3-MC-treated rats. The tumors appeared as multiple unilateral or bilateral subserosal nodes. No tumors were found in other tissues on gross inspection. Prior to necropsy, tumor-presenting animals were acyclic and arrested in a state of persistent proestrus. Haematoxylin and eosin staining of tumor sections revealed nests of acidophilic granule-containing cells within a highly vascular stroma of the uterine wall below the muscularis. Positive periodic acid Schiff (PAS) staining suggested the presence of glycogen or glycophospholipids within these granules, however, negative PAS diastase staining indicated that the acidophilic bodies were not composed of glycogen. The tumors are histologically similar to human dysgerminomas. We conclude that these tumors are unrelated to treatment and are of a granular type not previously documented in Wistar rats.

Vasopressin regulation of the proestrous luteinizing hormone surge in wild-type and Clock mutant mice

In the female mouse, ovulation and estrous cyclicity are under both hormonal and circadian control. We have shown that mice with a mutation in the core circadian gene Clock have abnormal estrous cycles and do not have a luteinizing hormone (LH) surge on the afternoon of proestrus due to a defect at the hypothalamic level. In the present study, we tested the hypotheses that vasopressin (AVP) can act as a circadian signal to regulate the proestrous release of LH, and that this signal is deficient in the Clock mutant. We found that Avp expression in the suprachiasmatic nucleus (SCN) and AVP 1a receptor (Avpr1a) expression in the hypothalamus is reduced in Clock mutant mice compared to wild-type mice. Intracerebroventricular (i.c.v.) injection of AVP on the afternoon of proestrus is sufficient to induce LH secretion, which reaches surge levels in 50% of Clock mutant mice. The effect of AVP on the Clock mutant LH surge is mediated by AVPR1A, as co-infusion of AVP and an AVPR1A-specific antagonist prevents AVP induction of LH release, although infusion of an AVPR1A antagonist into wild-type mice failed to prevent a proestrous LH surge. These results suggest that reduced hypothalamic AVP signaling plays a role in the absence of the proestrous LH surge in Clock mutant mice. The results also support the hypothesis that AVP produced by the SCN may be a circadian signal that regulates LH release.

Estrogen Mediates Phosphorylation of Histone H3 in Ovarian Follicle and Mammary Epithelial Tumor Cells via the Mitotic Kinase, Aurora B

Cells of the ovarian follicle undergo extensive proliferation and differentiation from the time that the follicle escapes from the primordial state to its acquisition of ovulatory capacity. We examined the dynamic modification of the phosphorylation state of the histone H3 N-terminal tail in granulosa cells during follicular development. In rodent follicles, the granulosa cell H3 phosphorylation on Ser10 peaks during proestrus. This epigenetic mark is induced by both FSH and 17β-estradiol (E2), acting independently. E2-induced H3 phosphorylation fails to occur in mice with inactivated α-isoform of the nuclear estrogen receptor. E2 induction of histone phosphorylation is attenuated by cell cycle inhibition. Further, E2 induces the activity of the mitotic kinase, Aurora B, in a mammary tumor cell model where mitosis is estrogen receptor-α dependent. These results provide evidence for mitotic regulation in follicle development by estrogen and demonstrate a previously undiscovered mechanism for induction of cell proliferation in ovarian and mammary gland cells.

8-oxoguanine DNA glycosylase, but not Kin17 protein, is translocated and differentially regulated by estrogens in rat brain cells

8-oxoguanine DNA glycosylase and Kin17 are proteins widely distributed and phylogenetically conserved in the CNS. 8-oxoguanine DNA glycosylase is a DNA repair enzyme that excises 7,8-dihydro-8-oxoguanine present in DNA damaged by oxidative stress. Kin17 protein is involved in DNA repair and illegitimate recombination in eukaryotic cells. The present study evaluates the effect of ovarian hormones on the expression of both proteins in the magnocellular paraventricular nucleus of the hypothalamus and the bed nucleus of the stria terminalis in female and male rat brains. In the paraventricular nucleus, ovariectomy induced a significant decrease in the number of 8-oxoguanine DNA glycosylase-positive nuclei as well as in their relative fluorescent intensity as compared with ovariectomized-estradiol treated and proestrous groups. Confocal microscopy observation demonstrated that oxoguanine DNA glycosylase protein is located in the Hoechst-dyed nuclei and cytoplasm in male and ovariectomized rats. Surprisingly, following estradiol administration to ovariectomized and proestrous rats, the 8-oxoguanine DNA glycosylase immunolabeling was observed in the nucleolus, the cytoplasm and the dendrites of cells, while Kin17 protein was always localized in the cell nuclei. In the bed nucleus of the stria terminalis, the number of 8-oxoguanine DNA glycosylase-positive nuclei during proestrous was significantly lower than the number obtained in males and ovariectomized rats and similar to the number of ovariectomized-estradiol-treated groups. In contrast to these observations, no significant differences were observed in the expression of kin17 protein. Our results suggest that estrogens differentially regulate the expression of 8-oxoguanine DNA glycosylase, but not that of Kin17 protein, in specific regions of the rat brain and that estradiol can translocate the 8-oxoguanine DNA glycosylase protein within nuclei and to other subcellular compartments.

Estrous cycle alters naphthalene metabolism in female mouse airways

Previous studies have shown variability in naphthalene cytotoxicity, expression of CYP2F2 gene and protein, and naphthalene metabolism in random cycling female mice (NIH:Swiss). CYP2F2 metabolizes naphthalene to cytotoxic metabolites in lungs of mice. This study was designed to address the question: do hormonal changes associated with the estrous cycle alter metabolism of naphthalene in the lung? Adult virgin female mice were manipulated into defined stages of the reproductive cycle: estrus, proestrus, and noncycling. Cycling was confirmed by cytology on vaginal swabs. At specific cycle times, extrapulmonary (tracheal and bronchial) and intrapulmonary (bronchiolar) conducting airways were microdissected from the lung parenchyma and incubated with naphthalene, and the products of naphthalene metabolism were trapped and measured using high-performance liquid chromatography. Circulating estradiol levels were measured at necropsy using an enzyme-linked immunosorbent assay. CYP2F2 gene expression was determined by airway level using real-time reverse transcription-polymerase chain reaction and did not vary by estrous cycle stage in intrapulmonary airways but did in extrapulmonary airways. Metabolism of naphthalene varied significantly by estrous cycle stage with the highest level of total metabolism occurring in proestrus (when estrogen is lowest) in intrapulmonary airways. Total activity and metabolite profiles in both extrapulmonary and intrapulmonary airways were affected by cycle stage. We conclude that the hormonal patterns associated with different stages of the estrous cycle 1) alter metabolism of naphthalene in the lungs of mice and 2) alter naphthalene metabolism differentially in extrapulmonary versus intrapulmonary airways.

Progestins in the hippocampus of female rats have antiseizure effects in a pentylenetetrazole seizure model

PURPOSE

Progestins can have profound effects on seizure processes. However, the effects and mechanisms of progestins to modulate seizures have not been systematically investigated. The present studies were designed to characterize the effects of progestins to modulate pentylenetetrazole (PTZ)-induced seizures in female rats.

METHODS

In Experiment 1, ictal activity and plasma and hippocampal progesterone (P) and 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) levels of proestrous rats were compared with those of diestrous and ovariectomized (ovx) rats. Experiments 2 and 3 examined effects of ovx and replacement with vehicle, P, or 3alpha,5alpha-THP, systemically (Experiment 2) or to the hippocampus (Experiment 3) on seizures and plasma and hippocampal P and 3alpha,5alpha-THP concentrations.

RESULTS

Proestrous rats had reduced ictal activity and increased levels of P and 3alpha,5alpha-THP in plasma and hippocampus compared with diestrous or ovx rats (Experiment 1). Rats administered systemic P or 3alpha,5alpha-THP had significantly reduced ictal activity and increased plasma and hippocampal P and 3alpha,5alpha-THP levels compared with vehicle-administered rats (Experiment 2). Administration of P or 3alpha,5alpha-THP to the hippocampus of ovx rats significantly reduced seizure activity and increased hippocampal, but not plasma, levels of P and 3alpha,5alpha-THP compared with vehicle administration (Experiment 3).

CONCLUSIONS

Together, these data suggest that P can have antiseizure effects, and these effects may be due in part to actions of its metabolite, 3alpha,5alpha-THP, in the hippocampus.

Expression of glutamate receptor subunits in the hypothalamus of the female rat during the afternoon of the proestrous luteinizing hormone surge and effects of antiprogestin treatment and aging

The excitatory transmitter, glutamate has been implicated in the control of reproduction, hormone secretion and neuroendocrine regulation. The present study examined whether the hypothalamic expression of three key ionotropic glutamate receptor subunits (NMDAR1, GluR1 and GluR6) fluctuates significantly on proestrus in the rat, and whether treatment with the antiprogestin, RU486 affected glutamate receptor subunit expression. The studies revealed that NMDAR1, GluR1 and GluR6 mRNA levels in the mediobasal hypothalamus (MBH) and preoptic area (POA) fluctuate little throughout the day of proestrus. However, treatment with the antiprogestin, RU486 induced a significant elevation of GluR6 mRNA levels at 14.00 and 16.00 h on proestrus in the MBH, suggesting that endogenous progesterone (P4) may act to inhibit hypothalamic GluR6 levels. In support of this suggestion, exogenous P4 treatment to estrogen (E2)-primed ovariectomized (ovx) rats significantly suppressed GluR6 mRNA levels in the afternoon (12.00-16.00 h) in the MBH, and at 12.00 h in the POA, which preceded LH surge induction. Likewise, temporal examination of hypothalamic GluR6 protein levels in E2 + P4-treated young and middle-aged ovx rats revealed an early elevation from 12.00 to 14.00 h, which was followed by a fall from 16.00 to 20.00 h. The early elevation of GluR6 protein levels was most pronounced in the POA of the young rat, and this elevation was markedly attenuated in the middle-aged rat. As a whole, the studies suggest that glutamate receptor expression fluctuates little on proestrus in the hypothalamus, but that expression of the kainate GluR6 receptor subunit may be modulated by progesterone and aging.

Sex differences in hippocampal estradiol-induced N-methyl-D-aspartic acid binding and ultrastructural localization of estrogen receptor-alpha

Estradiol increases dendritic spine density and synaptogenesis in the CA1 region of the female hippocampus. This effect is specific to females, as estradiol-treated males fail to show increases in hippocampal spine density. Estradiol-induced spinogenesis in the female is dependent upon upregulation of the N-methyl-D-aspartic acid (NMDA) receptor as well as on non-nuclear estrogen receptors (ER), including those found in dendrites. Thus, in the male, the inability of estradiol to induce spinogenesis may be related to a failure of estradiol to increase hippocampal NMDA receptors as well as a paucity of dendritic ER. In the first experiment, we sought to investigate this possibility by assessing NMDA receptor binding, using [(3)H]-glutamate autoradiography, in estradiol-treated males and females. We found that while estradiol increases NMDA binding in gonadectomized females, estradiol fails to modulate NMDA binding in gonadectomized males. To further investigate sex differences in the hippocampus, we conducted a second separate, but related, ultrastructural study in which we quantified ERalpha-immunoreactivity (ERalpha-ir) in neuronal profiles in the CA1 region of the hippocampus in intact males and females in diestrus and proestrus. Consistent with previous reports in the female, we found ERalpha-ir in several extranuclear sites including dendrites, spines, terminals and axons. Statistical analyses revealed that females in proestrus had a 114.3% increase in ERalpha-labeled dendritic spines compared to females in diestrus and intact males. Taken together, these studies suggest that both the ability of estrogen to increase NMDA binding in the hippocampus and the presence of ERalpha in dendritic spines may contribute to the observed sex difference in estradiol-induced hippocampal spinogenesis.

Changes of melanin-concentrating hormone related to LHRH release in the median eminence of rats

The present research was carried out to study the distribution of melanin-concentrating hormone (MCH) fibers in the median eminence of rats and to evaluate if changes in the MCH content of the median eminence could be related to the release of LHRH. Immunocytochemical studies in the median eminence of males and estrous females showed the presence of MCH fibers, mainly in its internal layer. Diestrous and proestrous animals displayed MCH immunoreactivity in both the internal and external layers of the median eminence. Longitudinal sections of the median eminence in proestrous animals showed that MCH-immunoreactive (ir) density is higher at 12 than at 9 h in both layers of the median eminence. MCH was assayed by radioimmunoassay in median eminences of males and in females in all stages of the estrous cycle at 10 h. It was observed that the content of MCH at diestrus-1 and -2 was higher than in estrus and in male rats. In the day of proestrus, MCH and LHRH were assayed at 10, 12, 13, 14, 15 and 17 h. At 12 h, the content of MCH and LHRH showed the maximal values. At 13 h, MCH content showed a decline, while LHRH was still high. At 14 h, the LHRH content started to decrease. The present results suggest that MCH is involved in the regulation of LHRH release in the female rat.

Glucocorticoid counteracts the suppressive effect of tumor necrosis factor-alpha on the surge of luteinizing hormone secretion in rats

We have previously reported that tumor necrosis factor-alpha (TNF-alpha) suppressed pulsatile secretion of luteinizing hormone (LH) in adrenalectomized (ADX) rats, which was restored by replacement of glucocorticoid. In the present study, we examined the role of glucocorticoid in inducing the preovulatory LH surge under conditions of infectious stress. Intravenous injection of TNF-alpha (1 microg) into the proestrous rats at 1300 h attenuated the LH surge and decreased the number of oocytes ovulated. The inhibitory effect of TNF-alpha on the LH surge was blocked by pretreatment with indomethacin, suggesting that the effects of TNF-alpha were mediated by prostaglandins (PGs). On the other hand, ADX markedly enhanced the inhibitory effect of TNF-alpha on the LH surge and subsequent ovulation, which was almost completely restored by pretreatment with a subcutaneous injection of corticosterone (10 mg). These results suggest that glucocorticoid counteracts the inhibitory effect of the cytokines on the preovulatory LH surge by suppressing PG synthesis, and thereby helps to maintain reproductive function under infectious stress conditions.

Orexin A and B levels in the hypothalamus of female rats: the effects of the estrous cycle and age

OBJECTIVE

Orexins have been implicated in the regulation of several physiological functions including reproduction, energy balance and vigilance state. For successful reproduction, the precisely timed hormonal secretions of the estrous cycle must be combined with appropriate nutritional and vigilance states. The steroid- and nutritional state-dependent modulation of LH release by orexins, as well as an increase of vigilance, suggest that orexins may co-ordinate these functions in the course of the estrous cycle.

DESIGN

We studied the brain tissue levels of orexins in the course of the estrous cycle in young and middle-aged rats. Young cycling rats (3 months old) and irregularly/non-cycling (7-9 months old) female rats were inspected for vaginal smears and serum hormone levels.

METHODS

Tissue concentrations of orexin A and B were measured in the hypothalamus and lateral hypothalamus on different days of the estrous cycle.

RESULTS

Orexin A concentration in the hypothalamus of young cycling rats was higher on the day of proestrus 5-6 h after the lights were switched on than on the other days of the estrous cycle at the same circadian time. Orexin B concentration was higher on both the day of proestrus and the day of estrus as compared with the days of diestrus. The hypothalamic concentrations of both orexin A and B in the non-cycling middle-aged rats were lower than those in cycling rats on the days of proestrus and estrus.

CONCLUSIONS

We have concluded that the high hypothalamic concentration of orexins on the day of proestrus may contribute to the LH and prolactin surges. High orexin A levels may also contribute to the decreased amount of sleep on the day of proestrus.

Prenatal cocaine exposure decreases nigrostriatal dopamine release in vitro: Effects of age and sex

The present study examined the effects of prenatal cocaine (PCOC) exposure, age, sex, and estrous phase on the functional development of nigrostriatal dopamine (DA) neurons. Striatal tissue was obtained from prepubescent and adult rats of both sexes after bidaily exposure to saline (1 ml/kg) or cocaine (20 mg/kg/ml saline) from embryonic days 15-21. Tissue levels, basal release, and electrically evoked (1 or 8 Hz) overflow of endogenous DA and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), as well as their efflux in response to superfusion with the DA transport blocker, nomifensine (10 microM), were measured from superfused striatal slices. Generally, these measures were highest in tissue from males and adults. Tissue DA and DOPAC levels and the rate of DA turnover were unaffected by PCOC exposure. Slices from PCOC-exposed juvenile and adult male rats exhibited significantly reduced basal and electrically evoked DA release at both stimulation intensities, in conjunction with higher levels of presynaptic DA reuptake. Female rats were largely spared from the effects of PCOC exposure, and measures did not vary with estrous phase. These findings demonstrate that the effects of PCOC exposure on various parameters of nigrostriatal DA neuronal function are not uniform across age, sex, or phases of the estrous cycle. These novel alterations in nigrostriatal DA transmission are in need of independent replication, but they may have profound implications for behavioral activities regulated by these neurons and, thus, may provide a basis for sex-selective effects of PCOC in exposed humans. Possible mechanisms of deleterious effects of PCOC exposure in select groups are discussed.

Gene expression analysis of the pro-oestrous-stage rat uterus reveals neuroligin 2 as a novel steroid-regulated gene

In the present study, differential gene expression in the uteri of ovariectomised (OVX) and pro-oestrous rats (OVX v. pro-oestrus pair) was investigated using cDNA expression array analysis. Differential uterine gene expression in OVX rats and progesterone (P4)-injected OVX rats (OVX v. OVX + P4 pair) was also examined. The uterine gene expression profiles of these two sets of animals were also compared for the effects of P4 treatment. RNA samples were extracted from uterine tissues and reverse transcribed in the presence of [α32P]-dATP. Membrane sets of rat arrays were hybridised with cDNA probe sets. Northern blot analysis was used to validate the relative gene expression patterns obtained from the cDNA array. Of the 1176 cDNAs examined, 23 genes showed significant (>two-fold) changes in expression in the OVX v. pro-oestrus pair. Twenty of these genes were upregulated during pro-oestrus compared with their expression in the OVX rat uterus. In the OVX v. OVX + P4 pair, 22 genes showed significant (>two-fold) changes in gene expression. Twenty of these genes were upregulated in the OVX + P4 animals. The genes for nuclear factor I–XI, afadin, neuroligin 2, semaphorin Z, calpain 4, cyclase-associated protein homologue, thymosin β-4X and p8 were significantly upregulated in the uteri of the pro-oestrus and OVX + P4 rats of both experimental pairs compared with the OVX rat uteri. These genes appear to be under the control of P4. One of the most interesting findings of the present study is the unexpected and marked expression of the neuroligin 2 gene in the rat uterus. This gene is expressed at high levels in the central nervous system and acts as a nerve cell adhesion factor. According to Northern blot analysis, neuroligin 2 gene expression was higher during the pro-oestrus and metoestrus stages than during the oestrus and dioestrus stages of the oestrous cycle. In addition, neuroligin 2 mRNA levels were increased by both 17β-oestradiol (E2) and P4, although P4 administration upregulated gene expression to a greater extent than injection of E2. These results indicate that neuroligin 2 gene expression in the rat uterus is under the control of both E2 and P4, which are secreted periodically during the oestrous cycle.

LHRH release depends on Locus Coeruleus noradrenergic inputs to the medial preoptic area and median eminence

We tested the hypothesis that Locus Coeruleus (LC) inputs to the medial preoptic area (MPOA) and median eminence (ME) are essential for gonadotropin release. Proestrus and ovariectomized (OVX) rats were decapitated at 16:00 h. LC electrolytic lesion was performed at 11:00 h during proestrus and 24h before decapitation in OVX rats. Plasma luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured and MPOA and ME were microdissected for LHRH content measurement. In addition, FOS protein in LC and MPOA were studied in proestrus and OVX rats at 12:00, 15:00, and 17:00 h. On proestrus, LC lesion blocked the LH surge and only decreased plasma FSH; in OVX rats the lesion induced only a slight decrease on plasma LH without affecting FSH secretion. An increased content of LHRH in the MPOA and ME of both groups accompanied the decreases of plasma LH. In proestrus, the number of FOS-immunoreactive (FOS-ir) neurons increased from 12:00 to 17:00 h in the LC and MPOA. In OVX rats, there was an increase at 15:00 h in the LC and a decrease at 17:00 h in both areas. The number of FOS-ir neurons was lower in OVX than in proestrus animals. Thus, LC (1) is responsible, at least in part, for gonadotropin release through the activation of LHRH neurons, (2) is more closely related to the positive than the negative feedback, and (3) seems to show an intrinsic cyclic activity which is amplified by ovarian steroids.

Immunolocalization of sex steroid hormone receptors in the canine uterine tube and their relation to sex steroid hormone concentrations

The aim of this immunohistochemical study was to describe the cellular distribution of the estrogen receptor-alpha (ERalpha), progesterone receptor (PR) and androgen receptor (AR) in canine uterine tubes. Samples of uterine tubes were taken from dogs in different stages of the estrous cycle, and dogs that were pregnant or had just delivered. Nuclear staining for sex steroid hormone receptors was observed in the surface epithelium, stromal cells and smooth muscle cells of the muscular layer. Only slight differences in staining pattern were observed between the ampulla and fimbriae. The staining for ERalpha and PR showed changes throughout the estrous cycle. Some of these changes were related to changing concentrations of sex steroid hormones. High staining scores for ERalpha and PR were found during proestrus and low scores during early metestrus. The staining for AR showed only minor cyclic changes. However, during proestrus and estrus, cytoplasmic staining for AR was observed in differentiated secretory epithelial cells, when nuclear staining in these cells was nearly absent. For the three hormone receptors, stromal cells generally stained with a higher intensity than epithelial cells. It is likely that many steroid hormone actions on the epithelium are mediated through stromal cells. During pregnancy, rather high staining scores were found for ERalpha and AR in the uterine tube. This is in contrast to observations in the canine pregnant uterus.

Mechanism for normal splenic T lymphocyte functions in proestrus females after trauma: enhanced local synthesis of 17beta-estradiol

Trauma-hemorrhage and resuscitation (TH) produces profound immunodepression and enhances susceptibility to sepsis in males but not in proestrus females, suggesting gender dimorphism in the immune responses. However, the mechanism responsible for the maintenance of immune functions in proestrus females after TH is unclear. Splenic T lymphocytes express receptors for estrogen (ER), contain enzymes involved in estrogen metabolism, and are the major source of cytokine production; the metabolism of 17beta-estradiol was assessed in the splenic T lymphocytes of proestrus and ovariectomized mice by using appropriate substrates after TH. Analysis for aromatase and 17beta-hydroxysteroid dehydrogenases indicated increased 17beta-estradiol synthesis and low conversion into estrone in T lymphocytes of proestrus but not of ovariectomized mice. The effect of 17beta-estradiol on T lymphocyte cytokine release was reliant on ER expressions. This was apparent in the differences of ER expression, especially that of ER-beta, and an association between increased 17beta-estradiol synthesis and sustained release of IL-2 and IL-6 in T lymphocytes of proestrus females after TH. Because 17beta-estradiol is able to regulate cytokine genes, and the splenic T lymphocyte cytokine releases is altered after TH, continued synthesis of 17beta-estradiol in proestrus females appears to be responsible for the maintenance of T lymphocyte cytokine release associated with the protection of immune functions after TH.

Estrogen receptor beta messenger ribonucleic acid expression in the forebrain of proestrous, pregnant, and lactating female rats

Estrogen receptor (ER)beta is present in hypothalamic and limbic neurons of female rat brains, but little is known about its regulation under physiological conditions. To determine whether ER beta expression varies during physiological conditions in which sex steroid hormone profiles are significantly different, we used in situ hybridization to assess ER beta mRNA expression in the periventricular preoptic area, bed nucleus of stria terminalis, paraventricular nucleus, supraoptic nucleus, and the posterodorsal medial amygdala of female rats on proestrus, on d 22 of pregnancy, or on d 10 of lactation (L10). In the periventricular preoptic area, d-22 pregnant females had fewer ER beta-mRNA-expressing cells than did females at proestrus, but the level of ER beta mRNA expression per cell in pregnant females was higher than in the two other groups. In the paraventricular nucleus, no changes in ER beta mRNA expression were observed; whereas in the supraoptic nucleus, proestrous females had fewer ER beta-mRNA-expressing cells than L10 females. In the posterodorsal medial amygdala, proestrous females had a greater number of ER beta-mRNA-expressing cells than did L10 females. These results demonstrate that ER beta mRNA expression is differentially regulated in a brain-region-specific and temporal manner under physiological conditions and suggest that ER beta may participate in the regulation of estrogen-sensitive reproductive functions in female rats.

Angiotensin-(1-7): a novel peptide in the ovary

The present study was undertaken to investigate the presence of angiotensin-(1-7) [Ang-(1-7)] in the ovary and a possible role for it. Cycling female rats were killed in each phase of the estrous cycle, and ovarian Ang II and Ang-(1-7) were separated by HPLC and measured by RIA. The mean levels of Ang-(1-7) in proestrus and estrus were significantly higher than those in metestrus and diestrus (P < 0.05). Ang-(1-7) was also significantly higher in equine chorionic gonadotropin (eCG)-treated immature rats. Ang-(1-7) induced a significant increase in estradiol and progesterone production (P < 0.05) in the ovary of immature rats (24-25 d old) pretreated with eCG and perfused in a closed circuit system. This effect was blocked by A-779, a specific Ang-(1-7) antagonist (P < 0.05). The present data demonstrate the presence and physiological role of a novel renin-Ang system peptide in the ovary. The higher level of Ang-(1-7) in proestrus and estrus as well as in eCG-treated rats suggests the involvement of this renin-Ang system peptide in pre- and postovulatory events.

Tyrosine hydroxylase and norepinephrine transporter in sympathetic ganglia of female rats vary with reproductive state

In females, sympathetic activity varies with changes in reproductive status, but whether expression of proteins critical to the function of sympathetic neurons is also altered is unknown. Therefore, the present study tested the hypothesis that, in rat adrenal gland and superior cervical ganglia, the expression of tyrosine hydroxylase (TH) and the norepinephrine transporter (NET), measured using Western analysis, are changed during pregnancy and the estrous cycle. Compared to diestrus, pregnancy increased TH levels in both superior cervical ganglia and adrenal gland. Pregnancy was also associated with decreased NET levels in the superior cervical ganglia, but increased levels in the adrenal gland. Relative to diestrus, the pattern of changes of TH and the NET in rats during proestrus was generally similar to changes observed during pregnancy. To assess whether gonadal hormones were involved, ovariectomized rats were also studied and changes in serum estrogen and progesterone were assayed in a subset of animals in all groups. Variations in TH and the NET among all groups did not correlate with changes in either estrogen or progesterone, suggesting that the steroids were not exclusively responsible. In conclusion, reproductive status alters the expression of TH and the NET in adrenal gland and superior cervical ganglia of female rats, which could significantly influence the function of the sympathetic nervous system. However, the mechanism for these changes does not depend solely on changes in estrogen or progesterone.

Role of Na+ and Ca2+ channels in the preoptic LH surge generating mechanism in proestrous rats

We studied whether Na+ and Ca2+ channels are involved in the neural mechanism responsible for the surge of gonadotropin-releasing hormone (GnRH) in proestrous rats. In experiment 1, female rats in proestrus were i.p. injected at 1345 h with pentobarbital sodium (35 mg/kg) to block spontaneous surge of LH and electrical stimulation was applied between 1400 and 1600 h to the preoptic area (POA) together with POA injection of 0.5 microl saline containing the Na+ channel blocker tetrodotoxin (TTX) at a concentration of 1 microM, 2 microM, or 5 microM. Since 5 microM TTX completely blocked the increase in serum LH concentrations evoked by the POA stimulation, we used this concentration in experiment 2 to observe the TTX effect on the spontaneous LH surge. In experiment 2, bilateral injections of 1.5 microl of 5 microM TTX at 1430 h in the POA in proestrous rats postponed the peak time and reduced the peak level of the LH surge. In experiment 3, bilateral injections of 1.5 microl of 5 microM L-type Ca2+ channel blocker nifedipine at 1430 h in the POA completely blocked the LH surge. Since the cell bodies of GnRH neurons are primarily concentrated in the POA in rats, these results suggest that both voltage-sensitive Na+ channels and Ca2+ channels contribute to the generation of action potentials at GnRH cell bodies for the surge release of GnRH.

Estrogen levels regulate the subcellular distribution of phosphorylated Akt in hippocampal CA1 dendrites

In addition to genomic pathways, estrogens may regulate gene expression by activating specific signal transduction pathways, such as that involving phosphatidylinositol 3-kinase (PI3-K) and the subsequent phosphorylation of Akt (protein kinase B). The Akt pathway regulates various cellular events, including the initiation of protein synthesis. Our previous studies showed that synaptogenesis in hippocampal CA1 pyramidal cell dendritic spines is highest when brain estrogen levels are highest. To address the role of Akt in this process, the subcellular distribution of phosphorylated Akt immunoreactivity (pAkt-I) in the hippocampus of female rats across the estrous cycle and male rats was analyzed by light microscopy (LM) and electron microscopy (EM). By LM, the density of pAkt-I in stratum radiatum of CA1 was significantly higher in proestrus rats (or in estrogen-supplemented ovariectomized females) compared with diestrus, estrus, or male rats. By EM, pAkt-I was found throughout the shafts and in select spines of stratum radiatum dendrites. Quantitative ultrastructural analysis identifying pAkt-I with immunogold particles revealed that proestrus rats compared with diestrus, estrus, and male rats contained significantly higher pAkt-I associated with (1) dendritic spines (both cytoplasm and plasmalemma), (2) spine apparati located within 0.1 microm of dendritic spine bases, (3) endoplasmic reticula and polyribosomes in the cytoplasm of dendritic shafts, and (4) the plasmalemma of dendritic shafts. These findings suggest that estrogens may regulate spine formation in CA1 pyramidal neurons via Akt-mediated signaling events.

Effects of combined exposure to lead and cadmium on the hypothalamic-pituitary axis function in proestrous rats

The effects of lead and cadmium on the hypothalamic-pituitary axis were studied in proestrous rats. Adult female rats were treated intraperitonially with either lead acetate and cadmium acetate alone or in combination at a dose of 0.05 mg/kg daily for 15 days. Serotonin (5-HT) and norepinephrine (NE) levels decreased in individually and combined metal treated groups whereas dopamine (DA) levels were decreased only in the cadmium-exposed group. The pituitary levels of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were decreased significantly in cadmium and combined treatment groups. In contrast, lead exposure failed to cause any change in serum LH and FSH levels, whereas cadmium and combined treatments showed significant decrease in serum LH and FSH levels as compared with control. The accumulation of both metals increased in the hypothalamus and pituitary after treatment. These data suggest that the metal accumulation disrupts the regulatory mechanisms of the hypothalamic-pituitary axis where the effects produced by the combined treatment of metals are not additive.

Autocrine regulation of prolactin secretion by endothelins throughout the estrous cycle

We have previously found that the ovarian steroid background determines the efficiency of the endothelin-mediated autocrine feedback regulation of prolactin (PRL) secretion. In this study, we investigated the role of endogenous endothelins in regulating PRL secretion during the estrous cycle. Adult female rats representing different stages of the 4-d cycle were sacrificed by decapitation, and the anterior pituitary cells were enzymatically dispersed using collagenase and hyaluronidase. PRL secretion of individual lactotrophs was measured in a PRL-specific reverse hemolytic plaque assay, and the influence of endogenous endothelins on PRL secretion was assessed by applying the selective ET(A) receptor antagonist peptide, BQ123. Blocking the endothelin-mediated autocrine feedback resulted in an increase in PRL secretion when cells were obtained at proestrus, estrus, and diestrus-1, whereas PRL secretion was decreased at diestrus-2 by ET(A) receptor blockade. These observations suggest that endogenous endothelins are predominantly inhibitory during proestrus, estrus, and diestrus-1, whereas at diestrus-2 their influence on PRL secretion is stimulatory. Whereas the bell-shaped concentration-response curves with BQ123 at proestrus and diestrus-1 may indicate a transition state in which endogenous endothelins can be both stimulatory and inhibitory, at estrus the influence of endogenous endothelins is unequivocally inhibitory in nature. We propose that intensification of the endogenous endothelin- mediated negative feedback at estrus may play a role in restraining PRL secretion following the estradiol- induced proestrous PRL surge.

Proestrous surge of gonadotropin-releasing hormone secretion inhibits apoptosis of anterior pituitary cells in cycling female rats

Estrogen affects apoptotic cell death in estrogen-responsive tissues. The purpose of the present study was to examine dynamic changes in apoptotic cell death in the anterior pituitary gland during the estrous cycle and to investigate neuroendocrine regulation of these changes in cycling female rats. Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) for in situ detection of DNA strand breaks revealed that the number of TUNEL-positive anterior pituitary cells was changing during the estrous cycle, with a maximum in the morning of proestrus and a minimum in the morning of estrus. A similar pattern was observed with Bax immunostaining; however, no difference was observed in Bcl-2 immunostaining. Most of Bax-immunoreactive cells were identified as a subpopulation of gonadotropes. Pentobarbital administered in the afternoon of proestrus attenuated the decrease in TUNEL-positive or Bax-immunoreactive cells in the morning of estrus, although estradiol treatment failed to affect it. This action of pentobarbital was reduced by simultaneous treatment with an ovulation-inducing dose of gonadotropin-releasing hormone (GnRH), but not with progesterone, an ovarian steroid also released after GnRH treatment. These results suggest that anterior pituitary cells, mostly gonadotropes, undergo a cyclic change in apoptotic cell death during the estrous cycle and that the inhibition of apoptosis on estrus is due, at least in part, to the proestrous surge of GnRH secretion.