Preovulatory Release Of Luteinizing Hormone Research Articles

Epigenetic modification of Kiss1 gene expression in the AVPV is essential for female reproductive aging.

Female reproductive senescence is heralded by hypothalamus region-specific changes in the transcription of genes such as Kiss1 under estradiol (E2) positive feedback, associated with luteinizing hormone (LH) surge dysfunction and reproductive decline. The current study explored whether the anteroventral periventricular nucleus (AVPV) displayed epigenetic changes mediated by age-related dysregulation of gene expression and whether an epigenetic-based intervention could alleviate an aging-related neuroendocrine disorder. Chromatin immunoprecipitation sequencing (ChIP-seq) and ChIP-qPCR were used to assess the differential acetylation of histone H3 in the AVPV and the expression of genes in hormone-primed middle-aged rats. The association between acetylated histone H3 and Kiss1 expression and the underlying mechanisms of dysregulation were determined using pharmacological inhibitors and molecular experiments in vitro and in vivo. An AVPV gene expression program failed to initiate in middle-aged females displaying typical genome-wide hypoacetylation of histone H3, and this coincided with decreased LH. Hypoacetylation of histone H3 at the 3' intergenic region of Kiss1 in particular was associated with enhanced chromatin looping between the promoter and enhancer. Restoration of physiological histone H3 acetylation by intracerebroventricular injection of trichostatin A (TSA) restored the expression of Kiss1 by modifying chromatin looping and led to the restoration of Kiss1 neuronal activation and Kiss1 synthesis as well as circulating LH. These findings have revealed novel epigenetic-associated changes in gene expression in female reproductive aging. These results also suggest that HDAC enzyme-based treatment is a potential therapeutic approach for insufficient preovulatory LH release in aging females.

Determination of progesterone levels in the blood of cattle by liquid chromatography-tandem mass spectrometry and the relationship of steroid concentration with fertilization

The optimal conditions for determining the concentration of progesterone in the blood plasma of cattle were selected by high-performance liquid chromatography-tandem mass spectrometry, and the relationship of the level of this progestin with fertilization after treatment of cows with hormonal preparations was studied. It was found that the time of progesterone peak release under the selected chromatography mode is within 2.7 minutes, and the optimal precursor ion is [M+H]+ m/z=315.3. The developed technique makes it possible to determine the endogenous level of the steroid in the blood of cattle with high accuracy (up to hundredths of ng/ml). Analysis of progesterone concentration in cows at the time of the final injection of the prostaglandin analogue showed that animals with different reproductive status have no significant differences in the content of this steroid. The most statistically significant indicators were obtained on the day of insemination. Thus, in infertile cows, the hormone concentration was 1.9...4.2 times lower than in fertilized cows (P<0.05). The higher steroid content in fertilized animals at the time of insemination most likely reflects the ovarian response to the preovulatory release of luteinizing hormone and the readiness of the follicle for ovulation. Keywords: cattle; high-performance liquid chromatomass spectrometry; progesterone; synchronization of sexual cyclicity; fertilization; infertility.

Effects of unilaterally microinjecting ethanol in the preoptic-anterior hypothalamic areas of rats on ovulation.

Intragastric or intraperitoneal ethanol (EtOH) treatment inhibits reproductive functions in females and male rats. The area of the hypothalamus where these effects take place is unknown. As the participations of the preoptic-anterior hypothalamic area (POA-AHA) in regulating ovulation is asymmetric, this study aims to analyze the effects on 17β-estradiol(E2 ), progesterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH) serum levels, the messenger ribonucleic acid (mRNA) expression of estrogen receptor alpha (ERα) and beta (ERβ), and ovulation resulting from unilaterally microinjecting water or an EtOH solution into either side of the POA-AHA. The treatment consisted of microinjecting a 8.6 μM EtOH solution into either side of the POA-AHA. The study was performed on groups of adult cyclic rats at 09.00 hours on diestrus-1, and sacrificed on diestrus-2 at 13.00, on proestrus at 09.00 or 17.00 or on estrus at 09.00 hours. Ovulation rates were assessed in rats sacrificed on estrus. Hormonal serum levels were measured using radioimmunoassay, and as a function of ERα and ERβ mRNA expression in each side of the POA-AHA by reverse transcriptase polymerase chain reaction. EtOH treatment blocked ovulation and the preovulatory release of LH, and lowered E2 levels. Irrespective of the treated POA-AHA side, ERα mRNA expression was consistently lower in the left POA-AHA and higher on the right. EtOH treatment in the left POA-AHA decreased FSH serum levels and lowered ERβ mRNA expression. In turn, EtOH treatment on the right POA-AHA resulted in higher FSH levels and ERβ mRNA expression. The present results show that EtOH blocks the preovulatory surge of LH on the POA-AHA. The effects of EtOH treatment of preovulatory FSH surge on the POA-AHA are asymmetric (stimulative on the right and inhibiting in the left). The effects of EtOH treatment on preovulatory LH and FSH surge could be explained by the inhibition of ERα and ERβ mRNA expression, respectively.

Effects of methanolic extract of Asparagus pubescens root on sexual behavior and pituitary hormone secretion on Wistar rats during pregnancy and lactation

We investigated the effect of methanolic extract of Asparagus pubescens root on sexual behavior and on pituitary hormone secretion during pregnancy and lactation on Wistar rats. Different doses (0.25, 0.5, 1.0 and 1.5 g/kg) of the extract, given in a single bolus dose or in four (divided) daily injections (0.0625, 0.125, 0.25 and 0.375 mg/(kg day)), inhibited sexual behavior when given to proestrous females in a dose-dependent manner, with the high doses (1.0–1.5 g/kg) inhibiting significantly the lordosis quotient. All treated females showed aggressive behavior towards the males to a similar extent irrespective of dose. Fertilization rate, pregnancy, delivery and litter size were normal. Birth weight and growth rates of the pups were also unaffected indicating no deleterious effects of extract on offspring development. The extract had significant effects on preovulatory luteinizing hormone (LH), prolactin (PRL) and progesterone (P4) release. Divided doses of 1.0 and 1.5 g/kg significantly decreased preovulatory LH, PRL and P4 release. Administration of 0.5 or 1.5 g/kg in bolus dose, produced significant inhibition of preovulatory LH and PRL while 1.5 g/kg had no effect. Progesterone was not modified while 1.0 g/kg dose caused a decrease in GH. 0.25 g/kg produced a paradoxical increase in preovulatory PRL secretion, also seen on day 4 of pregnancy. During pregnancy, both dose regimens were effective in inhibiting the afternoon peaks in prolactin secretion at all dose levels with the exception of 0.25 g/kg. There were no effects on the second half of pregnancy or on the suckling-induced PRL release on day 3 postpartum. Circulating GH was scarcely affected on day 3 postpartum. All the results taken together, indicate that the contraceptive effects of the extract may be exerted through interference with neural mechanisms that control preovulatory hormone release and sexual behavior.

Testosterone antagonist (flutamide) blocks ovulation and preovulatory surges of progesterone, luteinizing hormone and oestradiol in laying hens

The preovulatory release of luteinizing hormone (LH) in the domestic hen occurs after the initiation of a preovulatory surge of testosterone. The objective of this study was to determine whether this testosterone surge has functional significance in the endocrine control of ovulation. Groups of laying hens (n = 10-22) were treated with the androgen receptor antagonist, flutamide, at 8 h intervals for 24 h at doses of 0, 31.25, 62.5, 125 and 250 mg. All doses reduced egg laying (P < 0.001), with the highest dose being the most effective. In a second study, laying hens (n = 9) were treated with 250 mg flutamide at 8 h intervals for 24 h with a control group being given placebo (n = 10). Blood samples were taken for hormone measurements at 2 h intervals for 18 h starting 4 h before the onset of darkness. The percentage of hens laying per day did not differ between groups before treatment (control, 88% vs flutamide, 86%). Ovulation was blocked in all hens treated with flutamide within 2 days while the control hens continued to lay at the pretreatment rate (80%). Preovulatory surges of plasma testosterone, progesterone, oestradiol and LH were observed in control hens but with the exception of testosterone, flutamide treatment blocked the progesterone, oestradiol and LH surges. LH concentrations declined progressively with time in the flutamide-treated hens. It is concluded that inhibition of testosterone action blocks egg laying and the preovulatory surges of progesterone, luteinizing hormone and oestradiol demonstrating a key role for the preovulatory release of testosterone in the endocrine control of ovulation in the domestic hen.

Effects of Estrogen on Serum Leptin Levels and Leptin mRNA Expression in Adipose Tissue in Rats

Objective: In this study, we examined changes in serum leptin levels during the estrus cycle and the role of estrogen in these changes. Methods: We measured serum leptin levels during normal estrus cycles in intact rats and estradiol-17β (E₂)-induced artificial estrus cycles in ovariectomized rats. Results: Serum leptin levels increased 1.6-fold from 4.2 ± 0.2 ng/ml during diestrus stage 2 to 6.7 ± 0.9 ng/ml during proestrus stage during the 4-day estrus cycle. During the E₂-induced estrus cycle, serum leptin levels increased 2.3-fold from 2.3 ± 0.1 ng/ml at estrus to 5.4 ± 1.2 ng/ml at proestrus. E₂ also increased serum leptin concentrations and leptin mRNA expression in adipose tissue of immature rats. Discussion: These findings suggest that increased serum leptin induced by estrogen during proestrus may trigger the preovulatory release of luteinizing hormone. Furthermore, our findings indicate that estrogen has a positive effect on leptin production in adipose tissue.

Role of endogenous opiates in glucoprivic inhibition of the luteinizing hormone surge and fos expression by preoptic gonadotropin-releasing hormone neurones in ovariectomized steroid-primed female rats.

In female mammals, the preovulatory luteinizing hormone (LH) 'surge' elicits ovulation and the subsequent transformation of Graafian follicles into corpora lutea, and is thus a critical component of successful reproduction. In light of evidence that this surge is impaired as a consequence of caloric restriction, the following experiments utilized pharmacological strategies to determine whether glucose substrate homeostasis influences the magnitude and/or duration of this pivotal hormonal event. Groups of oestrogen-and progesterone-primed ovariectomized (OVX) rats were injected intravenously (i.v.) with the glucose antimetabolite, 2-deoxy-D-glucose (2DG: 100 or 400 mg/kg), or the vehicle, saline, prior to onset of the expected LH surge. Other rats were pretreated with 2DG (100 microg/rat) or saline by an intracerebroventricular (i.c.v) route. While glucoprivation did not abolish the afternoon LH surge in these animals, mean plasma LH levels were significantly decreased in groups injected with the higher i.v. dose of 2DG or treated with this drug by an i.c.v route, relative to their vehicle-injected controls. In other studies, i.c.v delivery of the opioid receptor antagonist, naltrexone (NALT), partially reversed the inhibitory effects of 2DG on the gonadal steroid-induced LH surge. Dual-label immunocytochemistry of tissue sections from the preoptic area and anterior hypothalamus of OVX, steroid-primed rats revealed nuclear Fos-immunoreactivity (-ir) in a subpopulation of gonadotropin-releasing hormone-(GnRH-)immunopositive neurones prior to maximal preovulatory LH release. Animals pretreated with 2DG i.c.v showed a significant decrease in mean numbers of GnRH neurones exhibiting Fos-ir, whereas coadministration of 2DG and NALT resulted in numbers of double-labelled neurones that were similar to those detected in the non-drug-treated controls. These studies show that magnitude of the LH surge is decreased by glucose substrate imbalance, and that regulatory effects of this metabolic challenge on the reproductive neuroendocrine axis is correlated with alterations in the transcriptional activation of preoptic GnRH neurones by gonadal steroid positive feedback. The present results also support a role for central opiatergic neurotransmission in glucoprivic regulation of cyclic LH secretion in this animal model.

Neonatal androgenization potentiates the inhibitory effects of blood withdrawal on ovulation in the rat.

Rats treated on Day 5 of life with testosterone propionate (TP) were tested for their ovulatory response to pregnant mare's serum gonadotropin (PMSG) on the 30th day of life with and without cardiac puncture under ketamine/xylazine anesthesia. TP without cardiac puncture in doses of 0.625, 1.25, or 2.5 microg did not inhibit ovulation, but 5.0 microg of TP inhibited ovulation in 15 of 16 rats. When cardiac puncture was performed at 1900 hr in rats not given TP, seven of eight ovulated on Day 33. However, none of the rats that received either 1.25 or 2.5 microg of TP ovulated after cardiac puncture at 1900 hr, and only one of seven given the 0.625-microg dose ovulated. Thus, the stress of bleeding greatly enhanced the inhibitory effect of otherwise ineffective doses of TP. The preovulatory luteinizing hormone (LH) surge was delayed and diminished by neonatal TP in a dose-related manner in animals from which blood was drawn from a previously inserted catheter. When blood drawn from similarly TP-treated animals by cardiac puncture, serum levels of LH were further reduced. Progesterone, given at 1100 hr on Day 32, was capable of partially overcoming the inhibitory effects of the combined treatments on both ovulation and serum LH levels at all but the highest dose of TP tested (5.0 microg). We conclude that neonatal exposure to androgen sensitizes rats to ovulation-inhibiting factors, such as bleeding, in a manner which appears to delay as well as inhibit the preovulatory release of LH. Such early exposure to androgen, therefore, may determine the susceptibility of individuals to reproductive failure in adult life.

V. N. Babichev. Neuroendocrine Regulation of the Reproductive System

The problems raised by V. N. Babichev in this monograph on deciphering the central mechanisms of regulation of the pituitary gonadotropic function occupy one of the main places among other issues of neuroendocrinology. To study the sequence of events in neuroendocrine processes that contribute to the preovulatory release of luteinizing hormone is a very complicated but necessary task. In the last decade, neuroendocrinologists are no longer satisfied with a fairly well-studied system of the relationship between gonadaliberin - gonadotropins and sex steroids. The essential role of monoamines of central origin in the regulation of the synthesis and secretion of pituitary gonadotropins, which show their function through luliberins, is shown. Experimenters and clinicians now have rich material that deepens and significantly changes our understanding of the neuroendocrine control of the reproductive system. These literature data in combination with prof. V.N. Babicheva demanded their generalization, which was perfectly done in the peer-reviewed monograph. A comprehensive approach to the study of the entire reproductive function control system, carried out in the laboratory of physiology of the endocrine system of the Russian Academy of Medical Sciences, starting from the period of early ontogenesis, made it possible to specify the role of neurotransmitters such as norepinephrine, dopamine and serotonin in the regulation of the pituitary gonadotropic function, to determine the point of their application in the hypothalamus , the direction of the response from gonadotropins depending on the level of sex hormones in the blood. The starting role of norepinephrine in the mechanism of ovulatory release of gonadotropins has been established, while the main point of its application is the preoptic region. The main point of application of dopamine is the area of ​​the mediobasal hypothalamus, or rather, the arcuate core.

The number and distribution of detectable luteinizing hormone (LH)-releasing hormone cell bodies changes in association with the preovulatory LH surge in the brains of young but not middle-aged female rats.

The population of LHRH neurons was examined in young and middle-aged female rats at two different time points associated with the LH surge on proestrus. More immunopositive LHRH neurons were detected in the brains of young but not middle-aged females killed on the evening of proestrus (1830-2030 h) compared with those killed earlier in the afternoon (1300-1430 h). To facilitate the investigation of potential regional differences within the population, sections through the basal forebrain were divided into four areas based upon their rostral-caudal position. Whereas no change in detectability was observed in the most rostral subset of LHRH neurons, more LHRH perikarya were observed at the later compared to the earlier time point in the other three areas surveyed in the brains of young females. Only the increase observed in sections through the preoptic area, however, reached statistical significance. Computer assisted three-dimensional reconstruction of all LHRH neurons in sections through the preoptic area revealed a marked increase in a subgroup of LHRH neurons in the dorsomedial aspect of this region of the population. Changes in detectability of LHRH neurons in association with the LH surge suggest that these neurons may be involved in regulating preovulatory LH release. Examination of additional time points could reveal changes in other subgroups of LHRH neurons as well as significant changes in detectability of LHRH neurons in aging brains.

The number and distribution of detectable luteinizing hormone (LH)- releasing hormone cell bodies changes in association with the preovulatory LH surge in the brains of young but not middle-aged female rats

The population of LHRH neurons was examined in young and middle-aged female rats at two different time points associated with the LH surge on proestrus. More immunopositive LHRH neurons were detected in the brains of young but not middle-aged females killed on the evening of proestrus (1830-2030 h) compared with those killed earlier in the afternoon (1300-1430 h). To facilitate the investigation of potential regional differences within the population, sections through the basal forebrain were divided into four areas based upon their rostral-caudal position. Whereas no change in detectability was observed in the most rostral subset of LHRH neurons, more LHRH perikarya were observed at the later compared to the earlier time point in the other three areas surveyed in the brains of young females. Only the increase observed in sections through the preoptic area, however, reached statistical significance. Computer assisted three-dimensional reconstruction of all LHRH neurons in sections through the preoptic area revealed a marked increase in a subgroup of LHRH neurons in the dorsomedial aspect of this region of the population. Changes in detectability of LHRH neurons in association with the LH surge suggest that these neurons may be involved in regulating preovulatory LH release. Examination of additional time points could reveal changes in other subgroups of LHRH neurons as well as significant changes in detectability of LHRH neurons in aging brains.

Daily variations in the sensitivity of proestrous LH surge in the inhibitory effect of intraventricular injection of 5-HT or GABA in rats.

Intraventricular injection of 5-hydroxytryptamine (5-HT) into female rats at 11:00 h on the day of proestrus inhibited the preovulatory surge of luteinizing hormone (LH) and ovulation. A similar response was observed after the activation of the serotonergic system by stimulation of the median raphe nucleus. A diurnal rhythm of these responses was observed. In rats acclimated to a 14-h:10-h light:dark cycle the potency of 5-HT to inhibit the LH surge and ovulation was 2.06 and 2.3 times greater, respectively, when injected at 11:00 h than at 13:00 h. Also stimulation of the median raphe nucleus at 11:00 h was significantly more effective in inhibiting these parameters than stimulation at 13:00 h. Similarly, the ability of gamma-amino-butyric acid (GABA) to inhibit the preovulatory LH surge and ovulation was greater in rats injected in the morning than in the afternoon. The results of this study indicate that during proestrus the sensitivity of 5-HT and GABA to induce inhibition of preovulatory LH release and ovulation shows daily variations with maximal effect before the critical period.

Physiologically important role for central oxytocin in the preovulatory release of luteinizing hormone

Recently, our laboratory has provided evidence for a physiologically relevant stimulatory influence of oxytocin (OXY) on the preovulatory luteinizing hormone (LH) surge in cycling female rats. The present study evaluated whether this stimulatory effect of OXY on LH release is exerted at a central or peripheral site of action by comparing the ability of peripheral (intravenous) or central (intracerebroventricular) administration of OXY antisera to influence the preovulatory LH surge. The peripheral injection of a very large dose of OXY antisera (0.8 ml) caused a slight attenuation of the early stages of the LH surge. In contrast, the central administration of 5 μl of OXY antisera completely abolished the preovulatory LH surge. The data support the hypothesis that OXY exerts a physiologically important stimulatory influence on the preovulatory LH surge which is mediated primarily at a central site of action.

The Roles of Endogenous Opioids in the Inhibitory Action of the Hippocampus on Preovulatory of Luteinizing Hormone in Rats.

Whether endogenous opioid peptides were involved in the inhibitory action of the hippocampus (HPC) on luteinizing hormone (LH) release was studied examining the effect of naloxone, an opioid antagonist, on the inhibitory action of electrical stimulation of the HPC and also by examining the effect of metenkephalin administration in the HPC, on preovulatory release of LH in proestrous rats. In rats treated with saline at 13:00 h, either sham stimulation or electrical stimulation of the dorsal HPC, which was performed acutely under ether anesthesia, significantly inhibited the afternoon rise in serum LH. In animals treated with naloxone at a dose of 2.0 mg/kg body weight, the afternoon rise in LH appeared smaller than that in the control group. However, statistical analysis showed no significant difference in LH values compared to the control group. Direct administration of met-enkephalin at a dose of 10 micrograms at 13:00 h through a chronically implanted cannula in the HPC did not induce any significant change in the afternoon rise in LH, regardless of whether it induced behavioral seizures or not. The results suggest that opioid peptides in the HPC do not play a significant role in the inhibitory action of HPC on LH release. Opioids existing in areas other than the HPC may play a certain, but small role.

Evidence for the involvement of dopamine and 5-hydroxytryptamine in the regulation of the preovulatory release of luteinizing hormone in the domestic hen

Injections of the dopamine (DA) precursor l-dopa and the 5-hydroxytryptamine (5-HT) precursor 5-hydroxytryptophan, beginning 6 hr before the predicted preovulatory release of LH, abolished the LH surge and blocked ovulation. The inhibitory effect of the drugs on the preovulatory release of LH was not reversed by injection of progesterone. This showed that the drugs inhibited LH release by acting on the central nervous system rather than peripherally, by inhibiting the release of progesterone from the ovary. The turnover rates of DA and 5-HT were estimated during the ovulatory cycle in the median eminence, the posterior hypothalamus, and the anterior hypothalamus. The turnover rates of the two monoamines were estimated from their rates of accumulation after inhibiting their catabolism with the monoamine oxidase inhibitor pargyline. Turnover of DA and 5-HT in the median eminence was depressed during the preovulatory release of LH and decrease in the anterior hypothalamus when preovulatory LH levels were increasing. Observations were also made of changes in the concentrations of hypothalamic DA, 5-HT, noradrenaline (NA), and adrenaline (A) during the ovulatory cycle. Concentrations of DA, 5-HT, and NA increased in the anterior hypothalamus and decreased in the posterior hypothalamus during the 4hr before the peak of the preovulatory release of LH. These results strengthen the view that hypothalamic DA and 5-HT play a role in the regulation of the preovulatory release of LH by a reduction in inhibitory inputs on LHRH neurones.

Dynamic Changes in Neuropeptide Y Concentrations in the Median Eminence in Association with Preovulatory Luteinizing Hormone Release in the Rat

Abstract Neuropeptide Y (NPY) stimulates luteinizing hormone (LH) release in the rat by a dual action, one in the hypothalamus to excite LH-releasing hormone (LHRH) release and the other at the level of pituitary gonadotrophs to activate and/or potentiate LH release induced by LHRH. Because NPY produces effects similar to norepinephrine with which it may comprise an excitatory hypothalamic circuit, it was hypothesized that NPY concentrations in the hypothalamus would change in a time- and site-specific manner in association with the preovulatory LH surge on proestrus. Concentrations of NPY in individual nuclei of the preoptic-tuberal pathway and serum LH levels were estimated by radioimmunoassays in rats during diestrus 2 and proestrus. On proestrus, serum LH levels were basal between 1000 and 1400 h, rose significantly at 1500 h and plateaued between 1600 and 1800 h. Of the five neural sites examined, only NPY in the median eminence displayed marked fluctuations in close association with the LH surge. NPY concentrations were low between 1000 and 1300 h, and rose abruptly at 1400 h (P<0.05) preceding the onset of LH rise at 1500 h. These elevated levels were maintained until 1600 h, during which time serum LH rose to a plateau and then fell at 1800 h to the low range seen between 1000 and 1300 h. In contrast, the pattern of changes in NPY levels in the arcuate nucleus, suprachiasmatic nucleus and medial preoptic area, three additional sites in the preoptic-tuberal pathway known to participate in the preovulatory LH surge, were markedly different from that seen in the median eminence. In each of these three sites, NPY levels rose significantly at 1800 h from the values at 1000 to 1200 h with a slightly different time-course of increment. None of these areas exhibited changes in NPY concentrations on diestrus 2; NPY concentrations also were unaltered on diestrus 2 or proestrus in the ventromedial nucleus. The present observations of site-specific, dynamic changes in NPY levels on proestrus, in a manner previously documented for LHRH, support the hypothesis that a subset of NPY neurons terminating in the median eminence may be a component of excitatory neural circuitry that either independently or in co-action with the adrenergic system is responsible for the induction of preovulatory LH release.

Changes of the release of luteinizing hormone (LH) on the day of proestrus after lesions or stimulation of the raphe nuclei in rats

The effect of stimulation or lesion of the raphe nuclei on ovulation and on the release of luteinizing hormone (LH) on the day of proestrus was studied in unanesthetized, unrestrained rats. Electrochemical stimulation (anodic DC or 100 μA during 30 s) was applied at 12.00 h on the day of proestrus through chronically implanted stainless steel electrodes. Lesions were made by passing a cathodic current of 1 mA for 20 s through nichrome electrodes stereotaxically implanted and the rats were used 15–30 days later. Blood samples were obtained hourly from the freely behaving rats through a plastic cannula inserted into the external jugular vein. Stimulation in the medial raphe nucleus (MRn) resulted in blockade of ovulation and of the preovulatory LH release. On the contrary, no change of the normal pattern of LH surge nor in the number of ovulating rats was seen after stimulation of the dorsal raphe nucleus (DRn) or in rats stimulated in the mesecephalon outside these nuclei. Injection of p-chloropheylalamine (PCPA) into the MRn to block 5-hydroxytryptamine (5-HT) synthesis, prevented the effect of MRn stimulation, whereas injection of saline solution did not. Rats bearing lesions destroying the DRn showed decreased proestrous LH surge and blockade of ovulation whereas those with lesions of MRn ovulated normally. Rats with transverse cuts placed just behind the DRn exhibited normal LH release indicating that the effects of destroying the DRn is not due to the interruption of ascending fibers crossing the nucleus. Injections of PCPA in the DRn but not saline solution mimicked the effect of lesions. It is concluded that the serotonergic system influences the proestrus surge of LH, with the DRn playing a facilitatory role and the MRn an inhibitory role.

Aspects of the neuroendocrine control of ovulation and broodiness in the domestic hen.

The neuroendocrine control of ovulation and broodiness in the domestic hen involves complex interactions between hypothalamic neuropeptides, neurotransmitters, and ovarian steroids which regulate the secretion of luteinizing hormone (LH) and prolactin. Nuclear progesterone receptor is localized in many neurons throughout the hypothalamus but is absent from LHRH neurons. Hence, the positive feedback action of progesterone on LH release is not mediated by a genomic mechanism within the LHRH neuron. Precursors of 5-hydroxytryptamine (5HT) and dopamine (DA) inhibit the preovulatory release of LH, while the turnover rates of these neurotransmitters in the anterior hypothalamus decrease when preovulatory levels of LH are at their highest. Further, a population of receptors for 5HT which occurs in the anterior hypothalamus in laying birds is absent in nonlaying, incubating hens. Taken together, these observations suggest that the preovulatory surge of LH is mediated by a transitory decrease in the inhibitory action of 5HT and possibly DA, on the secretion of LHRH. Neurons containing 5HT may play a role in the regulation of prolactin release and, more specifically, in the control of broodiness. Drugs which enhance the function of 5HT neurons stimulate prolactin release while increased prolactin secretion in incubating hens is associated with an increase in the turnover of 5HT in the anterior hypothalamus. No receptors for 5HT were demonstrable in the anterior pituitary gland, showing that the prolactin-releasing activity of 5HT must be mediated by a prolactin-releasing factor (PRF). A candidate for a physiological PRF is vasoactive intestinal polypeptide (VIP).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of prolonged stress on the oestrous cycles and prolactin secretion in sheep

The effect of repeated and prolonged stimuli on the release of luteinizing hormone (LH) and the course of oestrous cycles was studied in sheep. Weak electric footshocks were administered in different phases of the cycle in a programmed schedule for 9 h daily during 3–4 days. The enduring and repetitive character of the stimuli was supposed to induce some emotional state which approximated to the so-called management stress. Plasma prolactin concentration was also determined in the pro-oestrous phase of the cycle to follow the interrelationship between the pre-ovulatory release of LH and this hormone. Five out of 26 ewes stimulated in different phases of the oestrous cycle showed inhibition in the release of LH and disturbances in the function of the ovaries (cystic or inactive ovaries). The disturbances of the oestrous cycles appeared not only in the course of the current cycle (in which stimulation was applied), but also in the subsequent ones. Increased plasma prolactin levels after stimulation seem not to have an inhibitory action on the pre-ovulatory LH release. The other cause of the observed disturbances in the course of the oestrous cycle, i.e. the impairment of neuro-hormonal regulation, is discussed.

Reinitiation of ovulatory cycles in pituitary stalk-sectioned rhesus monkeys: evidence for a specific hypothalamic message for the preovulatory release of luteinizing hormone.

Female rhesus monkeys received intermittently infused GnRH after their pituitary stalks had been sectioned and either a Teflon or a Silastic barrier had been placed between the cut ends of the stalk. This mode of GnRH infusion (1 μg/ min for 6 min each hour) caused follicular development and an increase in serum 17β-estradiol (E2) levels to between 200–300 pg/ml, but did not result in ovulation in animals with Teflon barriers. Basal serum LH and FSH levels in these animals were comparable to those observed in intact cycling monkeys. In three animals with Silastic barriers (0.13 or 0.65 mm thick), the identical GnRH treatment resulted in follicular growth and ovulation. To determine if Silastic membranes could serve as a barrier against GnRH, we constructed Silastic capsules (wall thickness, 0.65 mm), filled them with GnRH, and implanted them sc into ovariectomized hamsters primed with E2. There was an increase (P < 0.05) in serum GnRH in animals treated with GnRH capsules, and serum LH was greater (P < 0....