LH Pulse Amplitude Research Articles

An interactive physiological role of neuropeptide Y and galanin in pulsatile pituitary luteinizing hormone secretion

Both neuropeptide Y (NPY) and galanin (GAL) systems have been implicated in the excitatory regulation of pulsatile LH secretion in the ovariectomized rat. The present studies were designed to examine the possible interaction of these two neuropeptides in controlling episodic LH release by testing the effects of central infusion of antibodies (Ab) to NPY and GAL, alone or in combination; additional studies tested the effects of central administration of an antisense oligodeoxynucleotide (ODN) to NPY and GAL messenger RNA. Rats were ovariectomized, implanted with a cannula in the third ventricle, and used in experiments 2 weeks later. Central infusion, via Alzet osmotic minipumps, of IgG purified from an NPY Ab produced a dose-related suppression of pulsatile LH secretion. Although an Ab dilution of 1:10 was ineffective, a maximal inhibitory effect was obtained using an NPY Ab dilution of 1:1, which decreased the mean levels, pulse frequency, and pulse amplitude of LH. These parameters of episodic LH secretion were also significantly reduced by central injection of antisense NPY ODN compared to those in vehicle- or missense ODN-treated controls. Similar dose-related inhibitory effects on the parameters of LH secretion were seen after central infusion of GAL Ab. Furthermore, infusion of a combination of NPY Ab and GAL Ab, each at the ineffective dilution of 1:10, resulted in a profound inhibition of LH secretion equivalent to the pattern seen with the maximally effective 1:1 Ab dilution. These results strengthen the idea of a physiological role for both NPY and GAL systems in the mechanism underlying the LHRH pulse generator activity and further suggest that these two excitatory neuropeptides act in concert to generate pulsatile LHRH release.

Insulin, somatotropic, and luteinizing hormone axes in lean and obese women with polycystic ovary syndrome: common and distinct features.

The basic tenet of this investigation was that obesity is not a prerequisite in the development of polycystic ovary syndrome (PCOS), as indicated by the fact that 50% of PCOS women are not obese. Further, obesity itself is a disease entity with the common manifestation of insulin resistance/hyperinsulinemia with PCOS. Given recent evidence that insulin and GH may have gonadotropin-augmenting effects, we have determined the common and distinguishing features of neuroendocrine-metabolic dysfunctions of lean [body mass index (BMI), < 23 kg/m2] and obese (BMI, > 30 kg/m2) women with the classical form of PCOS. Insulin sensitivity, as determined by rapid i.v. glucose tolerance testing; 24-h dynamics of insulin/glucose levels, somatotropic [GH/GH-binding protein/insulin-like growth factor I (IGF-I)/IGF-binding proteins (IGFBP)], and LH axes; and their downstream effects on ovarian steroids were simultaneously assessed in eight lean PCOS and eight obese PCOS patients and an equal number of BMI-matched normal cycling controls. Our results show that insulin sensitivity was reduced 50% (P < 0.01) in lean PCOS from that in lean controls. There was a further decrease in obese controls (P < 0.01) and a 2-fold greater reduction (P < 0.001) in obese PCOS than in obese controls, suggesting that insulin resistance (IR) is a common lesion in PCOS, and that obesity contributes an additional component to IR in obese PCOS. Consistent with the degree of IR, the manifestation of compensatory hyperinsulinemia in lean PCOS was incipient, being evident only in response to meals (P < 0.05), and became overt during the 24-h fasting/feeding phases of the day in obese control (P < 0.001) with a 2- to 3-fold greater elevation (P < 0.001) in obese PCOS. An enhanced early insulin response to glucose occurs equally in obese control (P < 0.01) and obese PCOS (P < 0.05), but not in their lean counterparts. Considering the more profound IR and the associated hyperglycemia in obese PCOS, the magnitude of the early insulin release is inadequate, suggesting that beta-cell dysfunction exists in obese PCOS. Remarkable differences in the somatotropic axis were also observed; although 24-h GH pulse frequency and levels of IGF-I and IGFBP-3 were unaltered by either PCOS or obesity, the 24-h mean GH pulse amplitude was increased by 30% (P < 0.01) in lean PCOS in the presence of normal levels of high affinity GHBP and normal GH response to GHRH. In distinct contrast, the somatotropic axis in both obese control and obese PCOS was profoundly modified, with attenuation of GH pulse amplitude (P < 0.001) and GH response to GHRH (P < 0.001), resulting in a state of hyposomatotropinism with a more than 50% reduction (P < 0.001) of 24-h mean GH levels. In addition, GHBP levels were elevated 2-fold and were correlated inversely with GH (r = -0.81) and positively with insulin (r = 0.75) concentrations. IGFBP-I levels were suppressed in both obese groups, with a 4-fold greater reduction in obese PCOS than that in obese controls. Thus, the downstream effects of hyperinsulinemia on the somatotropic axis may include up-regulation of hepatic production of GHBP, suppression of IGFBP-1 (r = 0.82) and sex hormone-binding globulin (r = -0.69) levels, and a more than 3-fold increase in ratios of IGF-I/IGFBP-1 and estradiol-testosterone/sex hormone-binding globulin, thereby increasing their bioavailabilities. In contrast, LH pulsatility was unaffected by obesity alone. An accelerated LH pulse frequency was evident in both lean and obese PCOS (P < 0.001), whereas the mean 24-h LH pulse amplitude was increased in lean (P < 0.001), but not obese, PCOS patients. These events resulted in a 3-fold increase in 24-h mean LH levels in lean PCOS and a 2-fold increase in obese PCOS. Thus, increased LH pulse frequency and augmented LH response to GnRH are characteristic of PCOS, independent of obesity, and the presence of obesity in PCOS is associated with an attenuated LH pulse amplitude, not accounted f

Differential regulation of luteinizing hormone release by gamma-aminobutyric acid receptor subtypes in the arcuate-ventromedial region of the castrated ram.

We investigated the effects on LH secretion of infusing gamma-aminobutyric acid (GABA) agonists muscimol and baclofen (GABAA and GABAB receptor agonists, respectively) into either the medial preoptic area (mPOA) or the arcuate-ventromedial region (ARC-VMR) of the hypothalamus of castrated rams during the nonbreeding season. Bilateral microdialysis of artificial cerebrospinal fluid for 4 h followed by treatment with artificial cerebrospinal fluid, baclofen (1 mM), or muscimol (1 mM in the ARC-VMR, 250 microM in the mPOA) for 4 h was carried out on three separate occasions in random order. Simultaneously, jugular venous blood was collected at 10-min intervals, and plasma later was assayed for LH. The estimated dose of baclofen delivered to each unilateral microdialysis site was 7.9 micrograms; for muscimol, it was 1.1 micrograms for the mPOA and 4.5 micrograms for the ARC-VMR. In the mPOA, baclofen had no detectable effect, whereas muscimol had a delayed suppressive effect on mean LH (P < 0.01). In the ARC-VMR muscimol rapidly reduced mean LH (P < 0.01). In contrast, baclofen increased mean LH (P = 0.01) and LH pulse amplitude (P = 0.05) without altering the LH interpulse interval (P > 0.10). These results support the involvement of GABAA receptors in the mPOA in regulating LH secretory patterns. More importantly, both GABAA and GABA(B) receptors in the ARC-VMR appear to differentially modulate LH and, presumably, GnRH release. Whether GABA acts directly on the GnRH neuron or indirectly through other neural systems remains to be determined.

Stimulation of luteinizing hormone secretion by food intake: evidence against a role for insulin.

In adult male rhesus monkeys, 1 day of fasting leads to a profound suppression of LH secretion that is rapidly reversed with refeeding. To test the hypothesis that changes in insulin secretion during fasting and refeeding mediate the changes in LH secretion, blood samples for LH measurement were obtained between 0900-2400 h from adult male rhesus monkeys (n = 9) on 1) a day when monkeys were refed their normal meal after a day of fasting, and 2) a day when monkeys were refed their normal meal, but endogenous insulin secretion was suppressed. Diazoxide (7.5-9.5 mg/kg.h) caused a 40-99% suppression of postmeal insulin secretion. However, no significant differences in LH pulse frequency, pulse amplitude, or mean serum LH levels were detected between control and diazoxide trials, even in animals in which insulin was markedly suppressed. Further, no correlation existed between the degree of insulin suppression and the magnitude of the meal-induced stimulation of LH. We conclude that meal-induced insulin secretion does not provide the stimulus mediating the meal-induced increase in LH secretion.

Effect of bovine follicular fluid treatment and progesterone priming on luteal function in GnRH-treated seasonally anoestrous ewes

AbstractThe main objective of the present experiment was to investigate whether progesterone priming eliminates defective luteal function in seasonally anoestrous ewes induced to ovulate with pulsatile GnRH treatment by synchronizing the early stages of follicle development. This was achieved by suppressing and synchronizing the early stages of follicle development with bovine follicular fluid (bFF) and then investigating whether this was sufficient to eliminate defective luteal function following the induction of ovulation with GnRH. Ewes in group 1 (no. = 10) were injected s.c. with 2 ml bFF at 8-h intervals for a period of 3 days before the start of GnRH treatment. Animals in group 2 (no. = 10), ivhich served as positive controls, were given a single i.m. injection of 20 mg progesterone 3 days before the start of GnRH treatment, while those in group 3 (no. = 10), which served as negative controls, were injected with corn oil alone at this time. Ewes in all the three groups were induced to ovulate by administration of 2-hourly injections of GnRH (250 ng per injection) for 54 h. Frequent blood samples for LH, FSH, and oestradiol were collected around the time of both progesterone/bFF injections and GnRH treatment, as well as daily thereafter to monitor luteal function.The bFF injections given to animals in group 1 resulted in a significant (P&lt;0·001) suppression of FSH concentrations, followed by a rebound rise in concentrations after the cessation of treatment. GnRH treatment significantly (P &lt; 0·05) increased both mean LH pulse amplitude and overall mean LH concentrations in all the three groups, while LH pulse frequency was increased only in non-bFF-treated ewes. Plasma oestradiol concentrations 24 h after the start of GnRH treatment were significantly (P &lt; 0·05) higher in groups 2 and 3 compared with group 1. These differences in the patterns of oestradiol concentrations over time were associated with a significant (P &lt;0·05) delay in the onset of the pre-ovulatory LH surge in ewes treated witli bFF (group 1). However, there was no difference in either the duration or the height of pre-ovulatory LH surge between the three treatment groups. Ewes in all three treatment groups ovulated in response to GnRH treatment. However, both laparoscopic examination and plasma progesterone concentrations revealed that the incidence of normal luteal function was significantly (P &lt; 0·05) higher in group 2 (10/10) compared with groups 1 (2/10) and 3 (4/10), with no difference between groups 1 and 3. Overall, these results suggest that progesterone priming does not eliminate defective luteal function through synchronizing early stages offollicle development.

Naltrexone Treatment Restores Menstrual Cycles in Patients With Weight Loss-Related Amenorrhea

Objective To evaluate whether the efficacy of naltrexone administration in patients with hypothalamic amenorrhea correlates to the response to an acute naloxone test. Design Thirty patients with hypothalamic amenorrhea associated with weight loss were studied. After naloxone test (4mg in bolus IV) patients were divided in two groups: group A, nonresponsive (n=15) and group B, responsive (n=15). Group A underwent two cycles of hormonal replacement therapy with E 2 patches and medroxyprogesterone acetate. Then all patients were administered naltrexone at the dosage 50mg/d orally for 6months. A third group of 10 amenorrheic patients were treated with oral placebo with the same schedule. Results Plasma gonadal steroid levels increased in all patients and in 24 of 30 patients the menstrual bleeding occurred within 90days from the beginning of treatment. After 6months from naltrexone discontinuation, 18 of 24 patients still showed the occurrence of menstrual cycles. Luteinizing hormone plasma levels and LH pulse amplitude increased after 3months of treatment and remained unchanged 6months after naltrexone suspension. Plasma FSH levels did not show any change in any patient. The body mass index increased after 3months in all patients who menstruated. Patients treated with placebo did not show any significant change in gonadotropins and gonadal steroid plasma levels. Conclusionss The present study supports the efficacy of naltrexone therapy for patients with hypothalamic amenorrhea either responsive or nonresponsive to naloxone test.

Alpha adrenergic neurons inhibit luteinizing hormone pulse amplitude in breeding season ewes.

It is now clear that estradiol acts in the brain to inhibit LH pulse amplitude in breeding season ewes, but the neural mechanisms underlying this action of estradiol have yet to be determined. In this study, we performed four experiments to examine the role of alpha-adrenergic neurons in the control of LH pulse amplitude in the ewe. In the first experiment, implantation of the alpha-adrenergic antagonist phenoxybenzamine into the preoptic area (POA) during the follicular phase of the ovine estrous cycle significantly increased LH pulse amplitude. A similar stimulatory effect of POA implants of this antagonist was observed in estradiol-treated ovariectomized (OVX+E) ewes, but phenoxybenzamine implants had no effect in the absence of estradiol. In contrast, systemic administration of phenoxybenzamine decreased LH pulse amplitude in both OVX and OVX+E ewes. Finally, POA implants of the alpha 1-adrenergic antagonist, prazosin, increased LH pulse amplitude in OVX+E ewes, whereas the alpha 2-adrenergic antagonist, yohimbine, had no effect in these animals. These results suggest that a noradrenergic (or adrenergic) system acts in the POA via alpha 1-adrenergic receptors to inhibit LH pulse amplitude in the ewe. They also raise the possibility that this system may be involved in the negative feedback action of estradiol during the breeding season.

Metabolic interfaces between growth and reproduction. V. Pulsatile luteinizing hormone secretion is dependent on glucose availability.

To test the hypothesis that mechanisms controlling the secretion of LH are modulated by glucose availability, the acute effects of glucoprivation were studied. The model was the gonadectomized male lamb raised on a limited diet of artificial milk. The approach was to monitor LH secretion before and after the administration of a competitive antagonist of glucose metabolism, 2-deoxyglucose (2DG). We first determined whether LH secretion was influenced by glucose availability by administering 2DG at several doses. Peripheral administration of the glucose antagonist (240 and 480 mg/kg 2DG, single iv injection) transiently decreased LH pulse frequency, but not LH pulse amplitude. By contrast, LH secretion (frequency or amplitude) was not affected by lower doses (60 or 120 mg/kg) of the glucose antagonist. A second study was conducted to determine whether either the pituitary gland or the GnRH neurosecretory system per se is directly affected by short term glucoprivation. The competency of the pituitary was assessed by administering GnRH during the time when LH secretion is suppressed by pharmacological glucose blockade. Similarly, the function of the GnRH neurosecretory system was assessed by administering a GnRH secretagogue (N-methyl-D,L-aspartate) under the same glucoprivic conditions. In response to an optimized iv dose of 2DG, LH pulse frequency decreased. However, in lambs that received either GnRH or N-methyl-D,L-aspartate during the period of glucoprivation, LH pulse frequency was sustained at levels comparable to those before 2DG was given. To determine whether the effect of glucoprivation was central in origin, the glucose antagonist was administered into the lateral cerebral ventricle at 1/100th the doses used peripherally. Central administration of 2DG, independent of dose, transiently decreased LH pulse frequency, but not pulse amplitude. However, unlike the case with peripheral injection, plasma glucose values did not change after the administration of any dose of 2DG tested centrally. These findings indicate that glucose availability in the developing sheep influences LH secretion. Moreover, based upon analysis of LH pulse frequency, glucoprivation does not directly impair either the pituitary gland or the GnRH neurosecretory system. Collectively, these results suggest that glucose availability affects LH secretion by acting within the central nervous system at a detection site(s) peripheral to the GnRH neuron.

The gonadotropin secretion pattern in normal women of advanced reproductive age in relation to the monotropic FSH rise.

Women of advanced reproductive age are known to demonstrate subtle FSH elevations (monotropic FSH rise) while still retaining ovulatory function. The purpose of this study was to investigate the hypothesis that the physiologic basis for the monotropic FSH rise is an alteration in the secretion pattern of the GnRH pulse generator. The subjects were 11 normal women age 40-45 years who underwent 24 hours of frequent blood sampling in the follicular (EF) and/or midluteal (ML) phases of spontaneous menstrual cycles. The controls were 11 normal women age 20-25 years. The respective gonadotropin secretion patterns were analyzed for LH pulse frequency, mean LH and FSH levels, and LH pulse amplitude. There were no differences between the groups for estradiol (E2) and progesterone when the respective cycle phases were compared. The 24-hour mean FSH level was significantly increased in the older women in both the EF and ML phases. There were no differences between the groups in either cycle phase for LH pulse frequency, LH pulse amplitude, and mean LH levels. The results lend no support to the hypothesis that a slowing or other alteration of the GnRH pulse generator is the basis for the monotropic FSH rise in older ovulatory women. Other possibilities include the dynamics of E2 secretion or changes in FSH-modulating peptides (i.e., inhibin) in these women.

Life-long moderate caloric restriction prolongs reproductive life span in rats without interrupting estrous cyclicity: effects on the gonadotropin-releasing hormone/luteinizing hormone axis.

Restricting food intake to 60% that of ad libitum-fed rats results in an extended life span, reduced incidence of age-related diseases, and delayed reproductive senescence. We used this animal model to further elucidate the mechanisms whereby reproductive senescence is delayed. Female Sprague-Dawley rats (7 wk old) were calorically restricted (CR; n = 70) to 60% of the ad libitum(AL) intake measured in control rats (n = 70). Rats were individually housed under a 14L:10D cycle and fed daily within 1.5 h of lights-off. Body weights were monitored every 2 wk, and vaginal lavage was performed until rats were ovariectomized (OVX). Two weeks after OVX, when rats were 4, 12, or 18 mo of age, blood samples were taken via jugular cannulae every 6 min for 3 h, and the plasma was assayed for rat LH. The resulting profiles were examined through use of Cluster analysis for mean LH concentrations, LH pulse amplitude, and interval between LH pulses. CR rats grew at a slower rate, and then maintained body weights at approximately 76% that of AL controls between 4 and 17.5 mo of age. The onset of persistent estrus was delayed by 4 mo in CR rats. Average cycle length was longer (p < 0.01) by less than 0.5 days in CR compared with AL rats between 3.5 and 5.5 mo of age but not different between 6.5 and 11.5 mo. Mean levels of LH in OVX rats decreased with age (p < 0.01), increased with caloric restriction (p < 0.05), and decreased with declining cycling status of the animal prior to OVX (regular [reg] vs. irregular [ir] vs. persistent estrus [pe]; p < 0.05). The increased mean LH due to caloric restriction was attributed to an increase in mean pulse amplitude and not to a decrease in time interval between LH pulses. From these data we conclude that the beneficial effects of caloric restriction on reproductive longevity may be acting at the level of the hypothalamus and/or pituitary to enhance LH secretion and do not require a delay in puberty or a period of acyclicity.

Differential effects of short-term fasting on pulsatile thyrotropin, gonadotropin, and alpha-subunit secretion in healthy men--a clinical research center study.

In healthy subjects, short term fasting suppresses the hypothalamic-pituitary-thyroid and hypothalamic-pituitary-gonadal (HPG) axes, with decreased serum levels of TSH and LH. However, effects of fasting on pulsatile release of TSH, LH, FSH, and alpha-subunit are less clear. Eleven healthy young men each underwent two 2-day studies: a baseline study during normal caloric intake and a fasting study during 56 h of caloric deprivation. During the final 24 h of each study, blood samples were drawn every 15 min for measurement of serum TSH, LH, FSH, and alpha-subunit pulses. Fifty-six hours of fasting caused a 50% suppression of mean TSH levels and TSH pulse amplitude, without altering TSH pulse frequency. Nocturnal TSH pulse amplitude decreased by 60%, with abolition of the usual nocturnal TSH surge. Fasting suppressed mean LH levels and LH pulse amplitude by 30%, without affecting LH pulse frequency. In contrast, mean FSH levels only decreased by 13%, without changes in FSH pulse parameters, whereas mean alpha-subunit levels and pulse amplitude decreased by 20%. These data show that short term fasting has a greater suppressive effect on the hypothalamic-pituitary-thyroid axis than on the HPG axis. Within the HPG axis, FSH is more resistant to fasting-induced suppression than LH, implying discordant regulation of the two gonadotropins during nutritional deprivation. alpha-Subunit suppression during fasting appears to parallel that seen for LH.

Sex steroids, growth hormone, insulin-like growth factor-1: neuroendocrine and metabolic regulation in puberty.

The control of the onset of puberty involves the complex interaction of pituitary and gonadal hormones. At a preprogrammed time in a child's life there is an increase in the amplitude of GnRH pulses which triggers a cascade of events including increases in the amplitude of FSH and LH pulses, followed by marked increases in gonadal sex steroidal output, which in turn increases growth hormone (GH) and insulin-like growth factor-1 (IGF-1) production. Evidence suggests that there is an integral interaction between the endogenous opiate system and the hypothalamic-pituitary-gonadal axis, at least in the later stages of puberty in the male. Both androgenic and estrogenic hormones markedly increase GH production rates as measured by deconvolution models in the prepubertal human, and compelling data strongly suggest that it is indeed the estrogen which controls the feedback amplification of GH production during puberty even in the male. It appears that the prepubertal gonad is actively producing sex hormones which might be important in the control of GH production since early childhood. The translation of these neuroendocrine rhythms into distal metabolic actions is also reviewed. Utilizing isotopic tracer infusions of the essential amino acid leucine, studies clearly show a selective stimulation of whole body protein synthesis by both GH and IGF-1. GH, IGF-1 and androgenic hormones all increase in puberty, stimulating whole body protein anabolism during that period. However, we observed no protein-anabolic effect in the hypogonadal female given increasing doses of estrogen. The latter suggests that at least as it pertains to whole body protein effects, the action of androgens is probably mediated via the androgen and not the estrogen receptor, in clear distinction from the estrogen-mediated effects of androgens on the neuroendocrine axis. Calcium absorption and retention are also positively affected by the androgens as shown by significant increases in calcium absorption and retention after the administration of testosterone to the prepubertal male. This suggests an important role of sex steroidal hormones in the mineralization of the skeleton. GH, IGF-1 and sex steroids all markedly increase during puberty and their actions are amplified mutually as they control growth, increase muscle mass and affect the mineralization of the skeleton. The dichotomy of androgen and estrogen effects in the male and female may regulate the differential timing of the onset of puberty and final height in the two sexes. The synergistic actions of these anabolic hormones appear to be most significant during the finite years of puberty.

Inhibition of ovulation by progestin analogs (agonists vs antagonists): Preliminary evidence for different sites and mechanisms of actions

Continuous administration of the antiprogesterone RU486 inhibits ovulation in women and in monkeys; in this regard RU486 may act as a progestin agonist rather than as an antagonist. We compared the site(s) and mechanism(s) of RU486-induced ovulation inhibition with those of levonorgestrel (LNG). Six regularly menstruating cynomolgus monkeys each received placebo, RU486 (1 mg/kg/d) or LNG (2 g/kg/d) im between days (cd) 2–22 of three separate menstrual cycles. Serum levels of estradiol (E 2), progesterone (P 4), androstenedione, LH and FSH were analyzed by RIAs in daily blood samples. Basal and GnRH-stimulated (1 and 50 g of GnRH iv 2 h apart) secretion of LH and FSH was assessed using serial blood samples collected for 12 h on cd 10. Mean cycle length was prolonged by RU486 and LNG treatments from 32 d to 70 d and 52 d, respectively (p < 0.02). Ovulation was inhibited in five of the six primates during RU486, and in all six during LNG treatment. During RU486 treatment, serum E 2 levels were similar to those of the control cycle; despite peaks of E 2 secretion, no LH peaks were seen. In contrast, E 2 concentrations were profoundly suppressed during LNG treatment (p < 0.005). The reduction in serum E 2 was accompanied by lower levels of androstenedione, and suppressed ratio of E 2/androstenedione (p < 0.02) suggesting both reduced synthesis and aromatization of androgen precursors during administration of LNG. Consequently, LNG treatment was associated with higher levels of serum FSH and LH (p < 0.0001; 1-way ANOVA). Similarly, as during the luteal phase of the menstrual cycle, the amplitude of basal LH-pulses was increased during LNG treatment (p < 0.05), whereas RU486 treatment did not affect basal LH secretion. The GnRH-stimulated release of LH was similar during the placebo, RU486 and LNG cycles; enhanced release of FSH was seen during administration of LNG. Thus, in the present model system, RU486 seems to inhibit ovulation mainly at the level of hypothalamus, possibly by interfering with the steroidal positive feedback signals from the ovary. However, LNG inhibits ovulation differently, most likely via direct progesterone-like effects on folliculogenesis and the hypothalamus. The pituitary does not appear to be the major site of action(s) of RU486 or LNG. Thus, the differential mechanisms of ovulation inhibition by RU486 and LNG seem to result from lesser intraovarian impact of RU486 as well as dissimilar influences on tonic gonadotropin secretory levels. We conclude that when inhibiting ovulation, RU486 does not act as a progestin agonist, but rather, functions through a hypothalamic mechanism(s), which might be unique to RU486 as a progesterone antagonist.

Influence of imposed feed intake patterns during lactation on reproductive performance and on circulating levels of glucose, insulin, and luteinizing hormone in primiparous sows.

Thirty-six primiparous sows were assigned to one of five treatments designed to mimic the lactation feed intake patterns observed in a previous study of commercial farms: high energy intake (HHH) or low energy intake during each week of a 3-wk lactation (LLL), or reduced intake during wk 1 (LHH), wk 2 (HLH) or wk 3 of lactation (HHL). The metabolizable energy intake of sows was either 16.5 (H) or 6.5 (L) Mcal/d. Diets were equal in lysine, providing 45 g/d. The HHH sows had a shorter (P < .05) weaning-to-estrus interval (9 +/- 3.2 d) than the sows in the LLL (23 +/- 3.5 d), HLH (22 +/- 3.5 d), and HHL (18 +/- 3.2 d) groups. The LH pulse frequencies of HHH (d 14: 1.5 pulses/8 h; d 21: 2.1 pulses/8 h) were greater (P < .05) than those of LLL (.2 pulses/8 h) and HLH (.5 pulses/8 h) on d 14 and those of LLL (0 pulses/8 h) and HHL (.9 pulses/8 h) on d 21 of lactation. No differences (P > .1) in mean serum concentrations of LH were observed among treatment groups either on d 21 of lactation or on d 1 postweaning. When fed a low-energy diet, sows had lower (P < .05) concentrations of serum insulin and plasma glucose than did sows fed a high-energy diet. Our results indicate that energy intake during lactation influences circulating insulin and glucose levels and LH pulse frequency and amplitude during midlactation and during the postweaning period.

The role of neuropeptide Y (NPY) in the control of LH secretion in the ewe with respect to season, NPY receptor subtype and the site of action in the hypothalamus

Neuropeptide Y1-36 (NPY1-36) acts through Y1 and Y2 receptors while the C-terminal NPY fragments NPY18-36 and N-acetyl[Leu28,31]pNPY24-36 act only through the Y2 receptor. We have investigated the effects of intracerebroventricular (i.c.v.) administration of NPY1-36, NPY18-36 and N-acetyl[Leu28,31]pNPY24-36 on LH secretion in the ovariectomised (OVX) ewe. These peptides were administered into a lateral ventricle (LV) or the third ventricle (3V) of OVX ewes during the non-breeding and breeding seasons. Microinjections of NPY were also made into the preoptic area (POA) during both seasons to investigate the effects of NPY at the level of the GnRH cell bodies. Tamed sheep were fitted with 19 gauge guide tubes into the LV, 3V or the septo-preoptic area (POA). Jugular venous blood samples were taken every 10 min for 3 h. Sheep were then given NPY1-36 (10 micrograms), NPY18-36 (100 micrograms) or saline vehicle into the LV; N-acetyl[Leu28,31]pNPY24-36 (100 micrograms), NPY1-36 (10 micrograms or 100 micrograms), NPY18-36 (10 micrograms or 100 micrograms) or saline vehicle into the 3V, or NPY1-36 (1 microgram, 5 micrograms, 10 micrograms) into the POA. Blood sampling continued for a further 3 h. LH was measured in plasma by radioimmunoassay. LV or 3V injection of 10 micrograms NPY1-36 caused a small but significant (P < 0.025) increase in the interval from the last pre-injection pulse of LH to the first post-injection LH pulse during the breeding season. Other LH pulse parameters were not significantly affected. NPY18-36 did not produce any significant change in LH pulsatility when injected into the LV, and neither peptide had any effect on plasma prolactin or GH levels. There was a significant (P < 0.01) reduction in LH pulse frequency after 3V injection of 10 micrograms and 100 micrograms NPY and 100 micrograms NPY18-36. Pulse amplitude was reduced by 3V administration of the Y2 agonist, N-acetyl[Leu28-31]pNPY24-36 and 100 micrograms NPY18-36. When the amplitude of the first post-injection LH pulse was analysed, 10 micrograms NPY also had a significant (P < 0.05) suppressive effect. During the non-breeding season, 100 micrograms NPY1-36 (but not 10 micrograms) decreased (P < 0.01) LH pulse frequency. LH pulse amplitude was significantly (P < 0.01) decreased by 100 micrograms NPY18-36. Doses of 10 micrograms NPY1-36 and 100 micrograms NPY18-36 had greater inhibitory effects on pulse frequency during the breeding season but the suppressive effect of 100 micrograms NPY was similar between seasons. Microinjections of NPY into the POA decreased (P < 0.01) average plasma LH levels during the non-breeding season at a dose of 10 micrograms but did not significantly affect pulse frequency or amplitude. We conclude that a substantial component of the inhibitory action of NPY on LH secretion in the absence of steroids is mediated by the Y2 receptor. This inhibition is probably exerted by way of a presynaptic action on GnRH terminals in the median eminence as NPY does not modulate the frequency or amplitude of LH pulses at the level of the GnRH cell bodies in the POA.

Short-term endocrine response to gonadotropin-releasing hormone agonist initiated in the early follicular, midluteal, or late luteal phase in normally cycling women

To determine short-term pituitary and ovarian hormonal responses to GnRH agonist (GnRH-a) administered during various phases of the menstrual cycle, in the absence of controlled ovarian hyperstimulation (COH), to determine its independent effect on hormonal parameters previously demonstrated to influence assisted reproductive technology cycle outcome.Prospective, randomized, controlled crossover study of five regularly cycling women. The GnRH-a, leuprolide acetate (LA), was administered 1 mg SC daily for 5 days beginning on cycle day 3 (early follicular); 8 days post-LH surge (midluteal); or 13 days post-LH surge (late-luteal).Clinical research unit at a tertiary care medical center.Serum gonadotropins (LH and FSH) and gonadal steroids (E2, estrone [E1], P, A, and T) measured daily during GnRH-a administration begun in the early follicular, midluteal, or late luteal phase of the menstrual cycle. Gonadotropin pulse amplitude and frequency were determined after frequent serum sampling on the 2nd day of GnRH-a administration in each treatment cycle.Serum LH elevations, 4- to 10-fold greater than observed for FSH, did not differ by cycle day of GnRH-a initiation. Initial increases in FSH did not differ by cycle day, however, early follicular initiation resulted in a more pronounced suppression of FSH. Mean LH pulse amplitude and frequency increased to a similar extent in all three groups, however, FSH pulse amplitude and frequency varied significantly by cycle day of GnRH-a initiation. Gonadotropin-releasing hormone agonist initiated in the early follicular phase resulted in significant increases in E2, E1, and P levels compared with both midluteal or late luteal. Increases in serum androgens were significantly greater after early follicular and late luteal initiation as compared with midluteal GnRH-a initiation.Relative FSH suppression and marked androgen elevations in both late luteal and early follicular groups, which may have potential detrimental effects on oocytes of the developing cohort, suggest little advantage of late luteal or early follicular over midluteal initiation of GnRH-a for COH.

Evidence for an altered luteinizing hormone sensitivity to naloxone in pathological hyperprolactinaemia

The underlying mechanisms involved in the pathogenesis of amenorrhoea in hyperprolactinaemic states still remain unclear. Conflicting information exists on the role of endogenous opiates on gonadotrophin disturbances in this pathological condition. In this study we have undertaken a detailed investigation of LH and PRL secretion before and during administration of naloxone, an opioid receptor blocker, in hyperprolactinaemic women with or without ovarian function in order to assess the role of ovarian steroids upon naloxone induced LH and PRL release. Five anovulatory and six ovulatory subjects with hyperprolactinaemia were studied before and during naloxone infusion. Five normo-prolactinaemic ovulatory subjects were included as controls. All ovulatory subjects were studied during the luteal phase of a menstrual cycle. Blood was sampled every 10-20 minutes over a 16-hour period on two alternate days. On study day 1 (control day), subjects received two sets of saline infusion every 6 hours and one saline bolus at the beginning of the seventh hour; on study day 3 (naloxone day), they received a saline infusion during the first 6 hours, an intravenous bolus of naloxone (20 mg) at the beginning of the seventh hour and then a continuous naloxone infusion (1.6 mg/hour) during the ensuing 6 hours. Pituitary LH responsiveness and reserve were assessed on both study days by the subsequent administration of 5 and 95 micrograms of GnRH 4 hours before the completion of each sampling period. Serum concentrations of LH, PRL, oestradiol and progesterone were determined by radioimmunoassay. LH and PRL pulse detection and characteristics were analysed by the Cluster program. Serum PRL levels in hyperprolactinaemic anovulatory and ovulatory subjects were significantly elevated above the normal range. Oestradiol and progesterone serum levels during the luteal phase in women with hyperprolactinaemia and regular menses were similar to those in control ovulatory subjects. Mean LH concentrations increased during naloxone infusion (P < 0.05) in ovulatory hyperprolactinaemia and controls, whereas PRL increased (P < 0.05) only in the group of control subjects. LH pulse amplitude and pulse interval were increased by naloxone (P < 0.05) in all the ovulatory subjects, with no significant changes in anovulatory hyperprolactinaemic women. PRL pulse characteristics were modified significantly by naloxone only in the control group. On day 1, GnRH administration increased LH in all groups, whereas a consistently lower pituitary LH response was observed after naloxone (day 3). Serum PRL levels significantly increased after GnRH administration on day 1 only in normal women, whilst on day 3 this GnRH-dependent PRL releasing effect was significantly attenuated. The absence of stimulatory effects of naloxone on LH in anovulatory hyperprolactinaemia implies that endogenous opiates do not play a significant role in the mechanisms governing hypothalamic amenorrhoea in this syndrome. The results in subjects with ovulatory hyperprolactinaemia suggest the existence of an active role of ovarian steroids on naloxone induced LH release. These data, along with those previously reported in normal women throughout the menstrual cycle, are consistent with the concept that sex steroid hormones contribute to the underlying mechanisms involved in the opioidergic control of LH and PRL release. Whether PRL by itself or through other non-opioid neuroendocrine pathways alters the hypothalamic-gonadotroph unit still requires further investigation.

Effects of infusion of GnRH pulses and level of body condition on ovarian function in postpartum beef cows

An experiment was conducted to test the hypothesis that postpartum anoestrus in beef cows is prolonged in cows in low body condition (BC) because they have a reduced LH pulse frequency compared with cows in high BC. Thirty-six multiparous Blue-Grey (White Shorthorn × Galloway) cows were fed so that they calved in either low (L) (BC score 2.07; SE 0.05; n = 24) or high (H) (BC score 2.81; SE 0.08; n = 12) body condition. They were then fed to maintain BC after calving. Twelve L cows were infused (i.v.) with 2 μg GnRH in 2 ml saline every 2 h from 5 to 7 weeks postpartum (LG) while the remaining L cows and all H cows were infused with saline only (LS and HS). Ovulations, as indicated by the presence of a morphologically normal corpus luteum, were recorded in one, one and ten of the cows of the LS, HS and LG groups, respectively. Mean LH concentrations and pulse frequencies were not affected by either GnRH treatment or BC but mean LH pulse amplitudes were lower ( P < 0.05) in LG and LS cows than in HS cows at Week 5 and in LG cows at Week 6. At Week 7 postpartum, the numbers of small (3–7.9 mm diameter) and large (≥ 8 mm diameter) ovarian follicles, mean granulosa cell numbers per follicle and mean concentrations of LH receptors (pg per mg thecal and granulosa tissue) were not affected by GnRH treatment or BC. Granulosa cells from oestrogen active follicles of HS and LG cows secreted more oestradiol in vitro ( P < 0.01) than cells from LS cows. However, there were no significant differences with treatment in the intrafollicular concentrations of oestradiol, testosterone or insulin-like growth factor-1. It was concluded that, since infusion of GnRH pulses enhanced both follicular steroidogenesis and the incidence of ovulation in low BC cows, the frequency of GnRH pulses is one determinant of follicle development in the postpartum cow. While H cows also exhibited a degree of enhancement of oestradiol synthesis by the granulosa cells of oestrogenic follicles, compared with L cows there was no difference in the LH pulse frequency or in the incidence of ovulation. It is concluded that there may be a threshold level of oestrogen synthesis by granulosa cells below which the final stages of follicle maturation and ovulation cannot be initiated, or that a high rate of oestradiol synthesis by this tissue is not the only factor mediating the effects of body condition on follicle development in the postpartum cow.

Naltrexone treatment restores menstrual cycles in patients with weight loss-related amenorrhea

To evaluate whether the efficacy of naltrexone administration in patients with hypothalamic amenorrhea correlates to the response to an acute naloxone test. Thirty patients with hypothalamic amenorrhea associated with weight loss were studied. After naloxone test (4 mg in bolus IV) patients were divided into two groups: group A, nonresponsive (n = 15) and group B, responsive (n = 15). Group A underwent two cycles of hormonal replacement therapy with E2 patches and medroxyprogesterone acetate. Then all patients were administered naltrexone at the dosage 50 mg/d orally for 6 months. A third group of 10 amenorrheic patients were treated with oral placebo with the same schedule. Plasma gonadal steroid levels increased in all patients and in 24 of 30 patients the menstrual bleeding occurred within 90 days from the beginning of treatment. After 6 months from naltrexone discontinuation, 18 of 24 patients still showed the occurrence of menstrual cycles. Luteinizing hormone plasma levels and LH pulse amplitude increased after 3 months of treatment and remained unchanged 6 months after naltrexone suspension. Plasma FSH levels did not show any change in any patient. The body mass index increased after 3 months in all patients who menstruated. Patients treated with placebo did not show any significant change in gonadotropins and gonadal steroid plasma levels. The present study supports the efficacy of naltrexone therapy for patients with hypothalamic amenorrhea either responsive or nonresponsive to naloxone test.

Involvement of N-methyl-D-aspartate receptor using excitatory amino acid neurotransmitters in control of pulsatile secretion of LH during sexual development in Holstein bull calves.

The neuroendocrine mechanisms underlying the development of pulsatile release of LH in bull calves are poorly understood. The hypothesis that endogenous excitatory amino acids, working through N-methyl-D-aspartate (NMDA) receptors, are involved in the generation of pulsatile LH release during sexual maturation of bull calves was tested. Holstein bull calves were administered i.v. 0.001, 0.01 and 0.1 mg kg-1 body mass of MK-801, a specific noncompetitive NMDA receptor antagonist, on alternate days at 1, 12 and 24 weeks of age (n = 6 per dose), using a replicated 3 x 3 latin square design. Blood samples were obtained from jugular catheters at intervals of 10 min for 2 h before and 2 h after MK-801 treatment at 1 week and for periods of 4 h before and after MK-801 administration at 12 and 24 weeks of age. Plasma concentrations of LH were measured by a specific radioimmunoassay and pulsatile LH secretion was analysed using the Pulsar algorithm. Basal LH secretion at 1 week of age was low but was increased by 12 weeks (0.38 +/- 0.01 versus 1.38 +/- 0.11 ng ml-1; P < 0.001) with the establishment of frequent high amplitude pulses. Mean LH concentrations and pulse amplitude, but not frequency, were lower at 24 than at 12 weeks of age (0.88 +/- 0.08 versus 1.38 +/- 0.11 ng ml-1: P < 0.001, 1.74 +/- 0.14 versus 2.82 +/- 0.36 ng ml-1: P < 0.01, and 1.70 +/- 0.30 versus 1.70 +/- 0.41 in 4 h: P > 0.05, respectively). Administration of MK-801 did not affect LH secretion in 1- and 12-week-old calves.(ABSTRACT TRUNCATED AT 250 WORDS)