LH Pulse Amplitude Research Articles

Prolactin regulation of testicular development and sexual behavior in yearling Suffolk rams

The aim of this study was to determine how the yearly prolactin rhythm might affect the sexual development of Suffolk rams (latitude 50°N). Five rams were injected daily with bromocriptine (35–45 μg kg −1 body weight) for 1 year, beginning in January (early winter) when rams were 11 months of age. Five control rams each received daily injections of the vehicle. In the controls, blood prolactin was <7.5 ng ml −1 in winter, increased ( P < 0.01) to a peak of 172.6 ± 11.9 ng ml −1 after the spring equinox, and remained high during summer before declining ( P < 0.01) to 29.6 ± 6.6 ng ml −1 at the autumn equinox. Suppression of the seasonal rise in prolactin secretion with bromocriptine slowed testicular growth (50%; P < 0.05) in April and May (spring), thus delaying the time of peak testis size and sperm production by 1 month. Serum testosterone level was lower (50%; P < 0.01) in the treated rams than the controls in June and July (early summer), due mainly to reduced stimulation of the testes by smaller ( P < 0.01) LH pulse releases or to smaller ( P < 0.01) testosterone responses to LH releases, respectively. Suppression of prolactin also seemed to disrupt the central activation of gonadotropin secretion in that seasonal increases in serum FSH level and LH pulse amplitude and frequency were unusually slow ( P < 0.05). These anomalies did not affect testis growth, which was normal from June until development was complete. Rams were sexually inexperienced when libido was first tested in July (non-breeding season). Both groups were equally capable of learning and expressing sexual behavior (i.e. normal mounting and ejaculation frequencies), which was more intense in September (breeding season; P < 0.05). Results support the hypothesis (based on the location of prolactin receptors) that the spring increase in prolactin secretion could target both the testes and the hypothalamic–pituitary system and be involved in the seasonal regulation of sexual function in the young adult Suffolk ram.

Central Lipoprivation-Induced Suppression of Luteinizing Hormone Pulses Is Mediated by Paraventricular Catecholaminergic Inputs in Female Rats

The present study aims to clarify the role of fatty acids in regulating pulsatile LH secretion in rats. To produce an acute central lipoprivic condition, mercaptoacetate (MA), an inhibitor of fatty acids oxidation, was administered into the fourth cerebroventricle (4V) in ad libitum fed ovariectomized (OVX) rats (0.4, 2, and 10 micromol/rat) with or without an estradiol (E2) implant producing diestrus plasma E2 levels. Pulsatile LH secretion was suppressed by 4V MA administration in a dose-dependent manner in both OVX and OVX plus E2 rats. Mean LH levels and LH pulse frequency and amplitude were significantly reduced by the highest dose of MA in OVX rats, and by the middle and highest dose of MA in E2-treated rats, suggesting that estrogen enhanced LH suppression. Blood glucose levels increased immediately after the highest dose of MA in both groups. Fourth ventricular injection of trimetazidine (2 and 3 micromol/rat), another inhibitor of fatty acids oxidation, also inhibited pulsatile LH release, resulting in significant and dose-dependent suppression of LH pulse frequency and an increase in blood glucose levels in OVX plus E2 rats. In contrast, peripheral injection of the highest 4V dose of MA (10 micromol/rat) did not alter LH release or blood glucose levels. Microdialysis of the hypothalamic paraventricular nucleus (PVN) revealed that norepinephrine release in the region was increased by 4V MA administration. Preinjection of alpha-methyl-p-tyrosine, a catecholamine synthesis inhibitor, into the PVN completely blocked the lipoprivic inhibition of LH and the counter-regulatory increase in blood glucose levels in OVX plus E2 rats. Together, these studies indicate that fatty acid availability may be sensed by a central detector, located in the lower brainstem to maintain reproduction, and that noradrenergic inputs to the PVN mediate this lipoprivic-induced suppression of LH release.

Inhibition of Luteinizing Hormone Secretion by Testosterone in Men Requires Aromatization for Its Pituitary But Not Its Hypothalamic Effects: Evidence from the Tandem Study of Normal and Gonadotropin-Releasing Hormone-Deficient Men

Studies on the regulation of LH secretion by sex steroids in men are conflicting. Our aims were to determine the relative contributions of testosterone (T) and estradiol (E2) to LH regulation and localize their sites of negative feedback. This was a prospective study with three arms. The study was conducted at a General Clinical Research Center. Twenty-two normal (NL) men and 11 men with GnRH deficiency due to idiopathic hypogonadotropic hypogonadism (IHH) participated. Medical castration and inhibition of aromatase were achieved using high-dose ketoconazole (KC) for 7 d with 1) no sex steroid add-back; 2) T enanthate 125 mg im starting on d 4; or 3) E2 patch 37.5 microg/d starting on d 4. Blood sampling was performed every 10 min for 12 h at baseline, overnight on d 3-4 and d 6-7. Mean LH levels, LH pulse amplitude, and GnRH pulse frequency were assessed at baseline, d 3-4, and d 6-7. In NL men, KC caused a 3-fold increase in mean LH on d 3-4, which was stable on d 6-7 with no add-back. Addition of T reduced LH levels (34.6+/-3.9 to 17.4+/-3.6 IU/liter, P<0.05) by slowing GnRH pulse frequency (13.3+/-0.4 to 6.7+/-1.0 pulses/12 h, P<0.005). LH amplitude increased (6.9+/-1.0 to 12.1+/-1.4 IU/liter, P<0.005). E2 add-back suppressed LH levels (36.4+/-5.6 to 19.0+/-2.4 IU/liter, P<0.005), by slowing GnRH pulse frequency (11.4+/-0.2 to 8.6+/-0.4 pulses/12 h, P<0.05) and had no impact on LH pulse amplitude. In IHH men, restoring normal T levels caused no suppression of mean LH levels or LH amplitude. E2 add-back normalized mean LH levels and decreased LH amplitude from 14.7+/-1.7 to 12+/-1.5 IU/liter (P<0.05). 1) T and E2 have independent effects on LH. 2) Inhibition of LH by T requires aromatization for its pituitary, but not hypothalamic effects. 3) E2 negative feedback on LH occurs at the hypothalamus.

Insight into the Neuroendocrine Site and Cellular Mechanism by which Cortisol Suppresses Pituitary Responsiveness to Gonadotropin-Releasing Hormone

Stress-like elevations in plasma glucocorticoids rapidly inhibit pulsatile LH secretion in ovariectomized sheep by reducing pituitary responsiveness to GnRH. This effect can be blocked by a nonspecific antagonist of the type II glucocorticoid receptor (GR) RU486. A series of experiments was conducted to strengthen the evidence for a mediatory role of the type II GR and to investigate the neuroendocrine site and cellular mechanism underlying this inhibitory effect of cortisol. First, we demonstrated that a specific agonist of the type II GR, dexamethasone, mimics the suppressive action of cortisol on pituitary responsiveness to GnRH pulses in ovariectomized ewes. This effect, which became evident within 30 min, documents mediation via the type II GR. We next determined that exposure of cultured ovine pituitary cells to cortisol reduced the LH response to pulse-like delivery of GnRH by 50% within 30 min, indicating a pituitary site of action. Finally, we tested the hypothesis that suppression of pituitary responsiveness to GnRH in ovariectomized ewes is due to reduced tissue concentrations of GnRH receptor. Although cortisol blunted the amplitude of GnRH-induced LH pulses within 1-2 h, the amount of GnRH receptor mRNA or protein was not affected over this time frame. Collectively, these observations provide evidence that cortisol acts via the type II GR within the pituitary gland to elicit a rapid decrease in responsiveness to GnRH, independent of changes in expression of the GnRH receptor.

Luteinizing hormone pulsatility in patients with major ovarian hyperandrogenism

Hyperandrogenism and ovulatory dysfunction are common in women with either polycystic ovary (PCOS) or ovarian virilizing tumor. However, contrasting with the numerous studies that have extensively described gonadotropin secretory abnormalities, principally increased LH pulse amplitude and frequency, few studies have concerned gonadotropin secretion in patients with ovarian virilizing tumors; low gonadotropin levels have occasionally been reported, but never extensively studied. The goal of the present study was to further evaluate the pulsatility of LH secretion in women with ovarian virilizing tumor compared with that of PCOS patients. Eighteen women with major hyperandrogenism (plasma testosterone level >1.2 ng/ml) were studied (5 women with ovarian virilizing tumor, 13 women with PCOS, and 10 control women). Mean plasma LH level, LH pulse number and amplitude were dramatically low in patients with ovarian tumors when compared to both PCOS (p<0.001) and controls (p<0.001). In case of major hyperandrogenism, LH pulse pattern differs markedly between women with ovarian virilizing tumor or PCOS, suggesting different mechanisms of hypothalamic or pituitary feedback.

Leptin Is a Metabolic Signal for GnRH-LH/FSH Axis in Feed-restricted Ewes

Two experiments were conducted to determine whether leptin is a metabolic signal for gonadotropin secretion in ewes. In the first experiment, twenty-eight cyclic Chal ewes were assigned randomly to an energy restricted, no leptin group (ERNL) (60% of maintenance; n = 14) and an energy normal, no leptin group (ENNL) (100% of maintenance; n = 14) for 71 days (6 estrous cycles). Estrus was synchronized with seven consecutive injections of PGF 2α . Biweekly, body weight (BW) and body condition score (BCS) were determined and blood samples were collected to measure plasma leptin concentration. Blood samples were also taken to determine plasma progesterone concentration twice weekly. After each PG injection from the second injection to the end of experiment, four ewes were selected and blood samples were collected at 20 minutes and at hourly intervals for 3 h to detect plasma LH and FSH concentration. In the second experiment, after the ceasing of the estrous cycle caused by energy restriction, six acyclic ewes were selected and randomly allotted to two groups (n = 3) and received the following treatment for four days. Ewes in an energy restricted, leptin group (ERL) were fed with a ration which provided 60% of maintenance energy requirements and intravenously injected with 4 μg leptin/kg BW daily. Ewes in an energy excess, no leptin group (EENL) were fed with a ration that provided 180% (120%+60%) of maintenance energy requirements and intravenously injected with 1 ml saline daily. In both groups, blood samples were collected at 20 minutes and at hourly intervals for 3 h before feeding on d 0 and d 5, and for 3 h before and after injections as above on d 2 and d 4 to detect plasma LH and FSH concentration. In the first experiment, BW and BCS from the 2 nd estrous cycle, and leptin from the 3 rd estrous cycle to the end of the experiment significantly (p<0.05) decreased. In ERNL ewes, mean plasma concentrations of FSH significantly (p<0.01) decreased from the 4 th estrous cycle to d 71 and LH pulsatile secretion was suppressed on d 71, so that, mean plasma concentrations of LH (p<0.05), LH pulse frequency (p<0.01) and LH pulse amplitude (p<0.05) significantly decreased. In the second experiment, injection of leptin significantly increased mean circulating concentrations of LH (p<0.05), LH pulse frequency (p<0.01), LH pulse amplitude (p<0.05) and mean circulating concentrations of FSH (p<0.01) and leptin (p<0.01). High energy intake significantly (p<0.05) stimulated pulsatile secretion of LH and leptin secretion (p<0.01), but non-significantly increased plasma FSH concentration. The results of this study indicate that leptin is a metabolic signal for the GnRH-LH/FSH axis in feed-restricted fat-tailed ewes.

Ghrelin Suppresses Secretion of Luteinizing Hormone in Humans

Ghrelin affects the hypothalamic-pituitary-gonadal axis in various nonhuman mammalians, predominantly by suppressing secretion of LH. However, for humans, no such evidence exists. Our objective was to study the effect of ghrelin on secretion of LH and testosterone in humans. Nocturnal (2000-0700 h) secretion profiles of LH and testosterone were determined in 10 healthy males (25.7 +/- 3.0 yr) twice, receiving 50 microg ghrelin or placebo at 2200, 2300, 2400, and 0100 h, in this single-blind, randomized, cross-over study. Ghrelin was associated with significantly (P < 0.05) lower mean plasma levels of both LH (2340-0200 h) and testosterone (0040-0300 h) than placebo. LH peak levels of the pulse after first administration of ghrelin/placebo were significantly (P = 0.014) smaller in the ghrelin (2.98 +/- 1.34 mIU/ml) than in the placebo condition (4.37 +/- 1.09 mIU/ml). In addition, the interval between this and the preceding peak was significantly (P = 0.010) longer in the ghrelin (255.8 +/- 79.1 min) than in the placebo condition (190.8 +/- 51.0 min). Significantly (P = 0.005) more LH pulses occurred with placebo (3.2 +/- 0.75) than ghrelin (2.6 +/- 0.7) subsequent to ghrelin/placebo administration. Ghrelin caused both a delay and suppression of the amplitude of LH pulses. These findings are in accordance with those in nonhuman mammalians.

Failure of short-term feed restriction to affect luteinizing hormone and leptin secretion or subcutaneous adipose tissue expression of leptin in the prepuberal gilt

Previously we reported that 24-h fast increased serum non-esterified fatty acids (NEFA) concentrations, and decreased leptin pulse frequency, but not mean serum leptin concentrations in the OVX prepuberal gilt. The present study was conducted to determine if short-term feed restriction in the prepuberal gilt would reduce BF gene transcript expression, pulsatile LH secretion and serum leptin concentrations. OVX prepuberal gilts 79 ± 4 kg BW were control fed 3 kg (CF; n = 6) or feed restricted (RST; 33% of CF diet; n = 6) for 8 d to determine the effects of RST on leptin and LH secretion, metabolism, leptin, Ob-rb and transcription factor expression in BF. Blood samples were collected on day 8 and BF on day 9. RST gilts lost BW (-2.5 vs. +8.2 kg; SE = 0.6 kg; P &lt; 0.001) and BF (-3 vs. +2 mm; SE = 1mm; P &lt; 0.02) compared with CF gilts. Postprandial serum T4 concentrations increased (P &lt; 0.04) in CF, but not in RST pigs. Postprandial serum insulin and BHBA concentrations were similar between treatments. A treatment × time interaction was detected for plasma glucose (P &lt; 0.02) and NEFA (P &lt; 0.04) concentrations. Feed restriction failed to affect leptin or LH secretion except for LH pulse amplitude was greater (P &lt; 0.01) in RST gilts. RST failed to affect BF leptin, Ob-rb, AFABP, C/EBPα, or PPARγ2 expression. In conclusion, the ability of the prepuberal gilt to maintain energy level in the normal range suggests the prepuberal animal is resistant to moderate reduction in nutrition. Thus, leptin may not play a primary role in the regulation of LH secretion in the prepuberal gilt, but may serve as a metabolic signal reflecting the amount of stored energy, which may be necessary for activation of the reproductive axis during puberal development in the gilt. Key words: Leptin, luteinizing hormone, nutrition, adipocyte, pig

Differential Effects of Various Estradiol-17beta Treatments on Follicle-Stimulating Hormone Peaks, Luteinizing Hormone Pulses, Basal Gonadotropin Concentrations, and Antral Follicle and Luteal Development in Cyclic Ewes1

In a previous study, 10-day estradiol implant treatment truncated the FSH peaks that precede follicular waves in sheep, but subsequent ovine FSH (oFSH) injection reinitiated wave emergence. The present study's objectives were to examine the effects of a 20-day estradiol and progesterone treatment on FSH peaks, follicle waves, and responsiveness to oFSH injection. Also, different estradiol doses were given to see whether a model that differentially suppressed FSH peaks, LH pulses, or basal gonadotropin secretion could be produced in order to study effects of these changes on follicular dynamics. Mean estradiol concentrations were 11.8 +/- 0.4 pg/ml, FSH peaks were truncated, wave emergence was halted, and the number of small follicles (2-3 mm in diameter) was reduced (P < 0.05) in cyclic ewes given estradiol and progesterone implants (experiment 1). On Day 15 of treatment, oFSH injection failed to induce wave emergence. With three different estradiol implant sizes (experiment 2), estradiol concentrations were 5.2, 19.0, 27.5, and 34.8 (+/-4.6) pg/ml in control and treated ewes, respectively. All estradiol treatments truncated FSH peaks, except those that created the highest estradiol concentrations. Experiment 2-treated ewes had significantly reduced mean and basal FSH concentrations and LH pulse amplitude and frequency. We concluded that 20-day estradiol treatment truncated FSH peaks, blocking wave emergence, and reduced the small-follicle pool, rendering the ovary unresponsive to oFSH injection in terms of wave emergence. Varying the steroid treatment created differential FSH peak regulation compared with other gonadotropin secretory parameters. This provides a useful model for future studies of the endocrine regulation of ovine antral follicular dynamics.

Effect of Continuous Intravenous Administration of Human Metastin 45–54 on the Neuroendocrine Activity of the Hypothalamic-Pituitary-Testicular Axis in the Adult Male Rhesus Monkey (Macaca mulatta)

In agonadal juvenile male monkeys, continuous administration of human metastin 45-54 (hu metastin 45-54) leads to desensitization of its receptor, G protein-coupled receptor 54 (GPR54), and decreased LH. The present study extended this observation to the adult male monkey, a more preclinically relevant model in which robust activity in the hypothalamic-pituitary-testicular axis is present. Continuous iv infusion of hu metastin 45-54 at either 200 or 400 microg/h elicited a marked rise in circulating LH that peaked 2-3 h after initiation of treatment. Thereafter, levels declined, and by 24 h, LH in metastin 45-54-infused animals was similar to control. LH release in response to an iv bolus of hu metastin 45-54 (10-30 microg) during the final 3 h of continuous infusion was truncated or abolished (low and high peptide dose, respectively). GPR54 desensitization by the high-dose metastin 45-54 infusion was associated with compromised pituitary response to a bolus GnRH injection (0.3 microg). LH pulse amplitude and pulse frequency were markedly suppressed during high-dose metastin 45-54 treatment. Surprisingly, the fidelity of the relationship between circulating testosterone (T) and LH was distorted during the high-dose peptide infusion. Thus, for a given concentration of LH, T levels were invariably higher during the high-dose metastin 45-54 infusion than during vehicle, suggesting that the peptide may exert direct actions on the testis to amplify T production. These findings support the notion that GPR54 is desensitized by continuous exposure to ligand, and they raise the possibility of an intratesticular role of GPR54.

LH pulsatile release patterns, follicular growth and function during repetitive periods of suckling and non-suckling in sows

This paper presents LH, estradiol, and cortisol in 12 sows that were separated from their piglets for 12 h a day, beginning around 2 w of lactation, until weaning (intermittent suckling, IS). To separate sows from their piglets, the sows either were moved to a different unit (total separation), or were only inhibited from suckling their piglets by a physical barrier (physical separation). Blood samples were frequently collected during 4.5 consecutive days. At the start of IS, four sows showed advanced follicle growth. In the eight remaining sows, total separation resulted in 4/4 sows ovulating, while physical separation resulted in 2/4 sows ovulating. Total and physical separation resulted in different LH secretion patterns. Total separation resulted in a lower amplitude of LH pulses than physical separation throughout the period of sampling (0.26 versus 0.53 ng/ml; P < 0.01), and seemed to result in an escape from inhibition of LH secretion during suckling. Similarly, sows that ovulated had a lower amplitude of LH pulses (0.30 versus 0.54 ng/ml; P < 0.05), and also showed a different effect of suckling on LH secretion than anovulatory sows. Total separation, in contrast to physical separation, consistently resulted in increased cortisol after separation ( P < 0.05). This contrast was not observed between ovulating and non-ovulating sows. We therefore conclude that IS results in an increased LH secretion. Inhibition of all contact between sows and piglets seems to result in a more sustained increase in LH secretion, which increases the chance of ovulation.

CIMICIFUGA RACEMOSA EXTRACT FOR THE TREATMENT OF CLIMACTERIC COMPLAINTS

Cimicifuga racemosa (CR) is widely used to treat climacteric complaints. These complaints, particularly hot flushes, are associated with over-activity of GnRH pulse generator in the hypothalamus, which is significantly reduced by E 2 . These effects can be ideally studied in ovariectomized (ovx) rats. In the present contribution we show that over-activity of GnRH pulse generator in the rat model is reduced by E 2 and by CR BNO 1055 as reflected in the reduced LH pulse amplitudes. This effect is not mediated by the pituitary because the extract had no effect on LH and TSH secretion but significantly inhibited prolactin release from cultured pituitary cells indicating the presence of dopaminergic compounds. Both, E 2 and CR treatment of ovx rats had profound effects on the expression of ER-alpha and ER-beta genes in the medio-basal hypothalamus and the preoptic area and both the compounds stimulated tyrosine hydroxylase gene expression in the preoptic area. This hypothalamic site is the location of GnRH perikarya. It can, therefore, be concluded that catecholaminergic mechanisms are involved in the modality by which the E 2 and CR inhibit the over-activity of the GnRH pulse generator in ovx rats and in postmenopausal women.

Progesterone acutely increases LH pulse amplitude but does not acutely influence nocturnal LH pulse frequency slowing during the late follicular phase in women

Progesterone (P) is the primary effector of LH (and by inference gonadotropin-releasing hormone) pulse frequency slowing in cycling women, but the time course of this action is unclear. We hypothesized that P administration to estradiol (E2)-pretreated women would slow LH pulse frequency within 12 h. We studied eight normally cycling women in two separate cycles (follicular phase, cycle days 7-11). After 3 days of E2 pretreatment (0.2 mg/day via transdermal patches), a 25-h blood sampling protocol (starting at 0800) was performed to define LH pulsatility. Oral micronized P (100 mg) or placebo (PBO) was administered at 1800 in a randomized, double-blind fashion, with treatment crossover occurring during a subsequent cycle. The 10-h mean P concentration increased from 0.6+/-0.1 ng/ml before P (0800-1800) to 3.9+/-0.3 ng/ml after P administration (2200-0800, P<0.01). Ten-hour mean LH interpulse interval increased significantly after both P and PBO administration, with no significant difference between P and PBO. In contrast, mean LH, LH amplitude, and mean FSH increased significantly within 4 h of P administration, but not after PBO. We conclude that, in E2-pretreated women in the late follicular phase, 1) nocturnal LH pulse frequency is not acutely (within 12 h) influenced by P administration; 2) an acute increase in P causes pronounced augmentation of gonadotropin pulse amplitude within 4 h; and 3) LH pulse frequency slows overnight during the second half of the follicular phase.

Sex Difference in the Suppressive Effect of Cortisol on Pulsatile Secretion of Luteinizing Hormone in Sheep

We tested the hypothesis that there are sex differences in the inhibitory effect of cortisol on pulsatile LH secretion and pituitary responsiveness to GnRH in gonadectomized sheep. In experiment 1, pulsatile LH secretion was examined in gonadectomized ewes and rams infused with either saline, a low (250 microg/kg.h) or a high (500 microg/kg.h) dose of cortisol for 30 h. In experiment 2, direct pituitary actions of cortisol were assessed by monitoring LH pulse amplitude in response to exogenous GnRH in hypothalamo-pituitary disconnected ewes and rams infused with the low dose of cortisol. In experiment 1, the mean (+/-sem) plasma LH concentration was (P<0.05) reduced significantly during cortisol infusion in both sexes, but the effect was greater in rams. In ewes, LH pulse amplitude and frequency were reduced (P<0.05) at the high, but not the low, cortisol dose, whereas total LH output (LH pulse amplitude multiplied by frequency) was reduced (P<0.05) at both doses. In rams, LH pulse frequency and amplitude and total LH output were (P<0.05) reduced significantly at both cortisol doses. In experiment 2, plasma LH concentration and pulse amplitude in response to exogenous GnRH were not affected by infusion of cortisol in either sex. We conclude that gonadectomized rams are more sensitive than gonadectomized ewes to the effects of cortisol to inhibit LH secretion and that sex differences exist in the specific actions of cortisol on LH pulses. The results of experiment 2 suggest that intact hypothalamic input to the pituitary is necessary for cortisol to inhibit pituitary responsiveness to GnRH.

Exogenous GH-releasing hormone increases GH and LH secretion in growing mithuns ( Bos frontalis)

To investigate the effects of growth hormone-releasing hormone (GHRH) administration on the patterns of GH and LH secretion in growing female mithuns, 12 mithuns within the age group of 10–12 months of age were divided into two groups (treatment and control groups) of six each in such a way that average body weight between the groups did not differ significantly ( P > 0.05). Both the groups were administered i.v. either with synthetic bGHRH [bGHRH (1-44)-NH 2] at 10 μg/100 kg body weight (treatment group) or equal volume of normal saline (control group). Blood samples collected prior to and after GHRH challenge at −60, −45, −30, −15, −10, −5 min and 5, 10, 15, 30 min, and thereafter, at an interval of 15 min up to 8 h post-injection were assayed for plasma GH and LH. Plasma progesterone was estimated in twice-a-week samples collected for six consecutive weeks preceding GHRH challenge to assess whether either group has begun ovarian cyclicity. Body weight of all animals was recorded once in a week during the period. A peak of GH was registered in all animals within 5–25 min post-GHRH administration with a mean peak of 443.5 ± 25.32 ng/ml at 15 min post-administration, which was much higher than in any other bovines reported following GHRH challenge. The patterns of LH secretion were pulsatile in nature in both the groups. Interestingly, the hormone concentrations exhibited higher pulsatility with greater amplitude after GHRH challenge in GHRH-treated than in control mithuns. The GHRH-treated mithuns averaged 0.44 pulses/h (4 pulses/9 h) and the rate was 0.20/h (2 pulses/9 h) in controls. The rate of pulse frequency and amplitude differed significantly with time of sampling. The mean plasma LH levels after GHRH administration were significantly higher in treatment group than those recorded in control mithuns. The mean plasma progesterone was similar ( P > 0.05) in both the groups and no animal from either group had begun ovarian cycle. In conclusion, exogenous GHRH significantly increases plasma GH and also LH pulse frequency and amplitude with higher mean post-GHRH LH levels in growing mithuns suggesting thereby its possible use for enhancement of maturity process in this unique meat animal.

Role of LH and prostaglandin F2α on the development and regression of corpus luteum in mithun ( Bos frontalis) estrous cycle

The present investigation was designed to study the role of LH and prostaglandin F2α (PGF2α) on the development and regression of corpus luteum (CL) in the mithun estrous cycle. Blood samples were collected from jugular vein and PGF2α secretion was evaluated on the basis of peripheral 15-keto-13,14-dihydro-PGF2α (PGFM) concentration. The daily variations in plasma LH, PGFM, and progesterone (P4) concentrations throughout the estrous cycle were monitored in morning and evening blood samples. The variations in plasma LH, PGFM, and P4 concentrations during the early luteal phase were monitored in blood samples that were collected every 2 h until 120 h following the onset of estrus (Day 0). The pulsatile secretion patterns of plasma LH, PGFM and P4 during estrus (Day1), mid-diestrus (Day 10), and luteolysis (Day 14) were assessed in blood samples that were collected every 15 min for 6 h. In the estrous cycle, P4 concentration increased above basal level on day 6–7, peaked on day 10–12 and declined thereafter. Following estrus, a significant ( P < 0.01) gradual increase in P4 concentration was observed. LH concentration was found to be significantly ( P < 0.01) greater around estrus and it declined gradually ( P < 0.01) following estrus. In the estrous cycle, PGFM concentration increased above basal level on day 9–11, peaked on day 16–17, and declined thereafter. The frequency of LH pulses and basal LH concentration were found to be significantly ( P < 0.01) greater on day 1, but significantly ( P < 0.01) greater amplitude of LH pulses was found on day 10 and 14. The frequency of P4 and PGFM pulses was found to be significantly ( P < 0.01) greater on day 1. In contrast, the amplitude of P4 and PGFM pulses and basal P4 and PGFM concentrations were found to be significantly ( P < 0.01) greater on day 10 and 14. The results indicate that probably the early stages of CL development continued until day 5–6 of the estrous cycle and a fully functional CL existed approximately at the mid estrous cycle. Luteolysis probably started since day 11–13 of the cycle and completed before the onset of the next estrus. The elevated basal LH concentration along with frequent low amplitude LH pulses were probably required for the early stages of CL development. In contrast, the high amplitude LH pulses of lower frequency during the mid estrous cycle were either sufficient or not required for maintaining the luteal function. Whereas, PGF2α pulses of greater amplitude and elevated basal PGF2α concentration during the mid and late estrous cycle were probably responsible for luteolysis.

The Response of Luteinizing Hormone Pulsatility to 5 Days of Low Energy Availability Disappears by 14 Years of Gynecological Age

The incidence of menstrual disorders declines during adolescence. The mechanism responsible is unknown. The objective of the study was to test the hypothesis, formulated a priori, that the dependence of LH pulsatility and ovarian function on energy availability declines with gynecological age (years since menarche). The study was a controlled experiment repeated in two menstrual cycles, performed 2001-2004. The study was conducted at a university laboratory and general clinical research center. The study population consisted of healthy, habitually sedentary, young women of normal body composition with 5-8 yr (adolescents, n = 9) and 14-18 yr (adults, n = 10) of gynecological age recruited by advertisement from approximately 9000 women aged 18-34 yr in a college community. Samples were similar in age of menarche, length of menstrual cycle and luteal phase, body size and composition, aerobic capacity, and dietary intake. None were withdrawn due to adverse effects. Interventions included energy availabilities of 45 and 10 kcal/kg of fat-free mass per day for 5 d in the early follicular phases of separate menstrual cycles in random order. LH pulsatility, estradiol, and luteal phase length were measured. Low energy availability reduced LH pulse frequency in adolescents (P < 0.01) but not adults (P = 0.39), did not increase LH pulse amplitude in either group (both P = 0.13), and suppressed 24-h mean LH in adolescents (P = 0.01) but not adults (P = 0.72). Estradiol was unaffected (both P = 0.48), but the subsequent luteal phase was shorter in adolescents (P < 0.01). In women of normal body composition, the response of LH pulsatility and ovarian function to 5 d of low energy availability disappears by 14 yr of gynecological age.

Comparative response of rams and bulls to long-term treatment with gonadotropin-releasing hormone analogs

The objective was to compare the relative response between rams and bulls in characteristics of LH, FSH and testosterone (T) secretion, during and after long-term treatment with GnRH analogs. Animals were treated with GnRH agonist, GnRH antagonist, or vehicle (Control) for 28 days. Serial blood samples were collected on day 21 of treatment, and at several intervals after treatment. Injections of natural sequence GnRH were used to evaluate the capacity of the pituitary to release gonadotropins during and after treatment. Treatment with GnRH agonist increased basal LH and T concentrations in both rams and bulls, with a greater relative increase in bulls. Endogenous LH pulses and LH release after administration of GnRH were suppressed during treatment with GnRH agonist. Treatment with GnRH antagonist decreased mean hormone concentrations, LH and T pulse frequency, and the release of LH and T after exogenous GnRH, with greater relative effects in bulls. Rams previously treated with antagonist had a greater release of LH after administration of GnRH compared with control rams, while rams previously treated with agonist showed a reduced LH response. Bulls previously treated with agonist had reduced FSH concentrations and LH pulse amplitudes compared with control bulls while bulls previously treated with antagonist had greater T concentrations and pulse frequency. The present study was the first direct comparison between domestic species of the response in males to treatment with GnRH analogs. The findings demonstrated that differences do occur between rams and bulls in LH, FSH and testosterone secretion during and after treatment. Also, the consequences of treatment with either GnRH analog can persist for a considerable time after discontinuation of treatment.

Inverse Relationship between Luteinizing Hormone and Body Mass Index in Polycystic Ovarian Syndrome: Investigation of Hypothalamic and Pituitary Contributions

Patients with polycystic ovarian syndrome (PCOS) have increased LH relative to FSH, but LH is modified by body mass index (BMI). The objective of the study was to determine whether the impact of BMI on neuroendocrine dysregulation in PCOS is mediated at the hypothalamic or pituitary level. PARTICIPANTS/INTERVENTIONS/SETTING: Twenty-four women with PCOS across a spectrum of BMIs underwent frequent blood sampling, iv administration of GnRH (75 ng/kg), and sc administration of the NAL-GLU GnRH antagonist (5 microg/kg) in the General Clinical Research Center at an academic hospital. LH pulse frequency and LH response to submaximal GnRH receptor blockade were used as measures of hypothalamic function; LH response to GnRH was used as a measure of pituitary responsiveness. BMI was negatively correlated with mean LH, LH/FSH, and LH pulse amplitude. There was no effect of BMI on LH pulse frequency. Percent inhibition of LH was decreased in PCOS, compared with normal women (53.9 +/- 1.5 vs. 63.1 +/- 4.1, respectively; P < 0.01), suggesting an increase in the amount of endogenous GnRH, but was not influenced by BMI. Pituitary responsiveness to GnRH was inversely correlated with BMI (peak LH, R = -0.475, P < 0.02; and LH area under the curve R = -0.412, P < 0.02). LH pulse frequency and quantity of GnRH are increased in PCOS, but there is no influence of BMI on either marker of hypothalamic function. The pituitary response to a weight-based dose of GnRH is inversely related to BMI in PCOS. These studies suggest that the effect of BMI on LH is mediated at a pituitary and not a hypothalamic level in PCOS.

Effects of metformin on inappropriate LH release in women with polycystic ovarian syndrome and insulin resistance

The role of hyperinsulinaemia in neuroendocrine abnormalities in polycystic ovarian syndrome (PCOS) is controversial. The present study applied frequent blood sampling to assess the response of LH to metformin treatment in insulin-resistant women with PCOS. Thirteen predominantly overweight women with PCOS were studied before and after treatment with 1.5 g/day metformin for 3 months. Serum LH and testosterone were measured every 10 min for 10 h; LH was measured for an additional 2 h after gonadotrophin-releasing hormone (GnRH) administration. LH pulses were characterized by cluster analysis, secretory LH episodes by a deconvolution procedure, and synchronicity of paired LH-testosterone concentrations by lag-specific cross-correlation. After treatment, basal LH concentrations, amplitude of LH pulses, LH secretory amplitude, response to exogenous GnRH, and basal testosterone concentrations significantly decreased in seven patients, whereas in the remaining women these parameters remained unaltered. Before treatment, decreased coordinate LH and testosterone release was manifested by all patients; metformin treatment led to re-establishment of the feed-back control of testosterone on LH secretory rates by −20 to 0 min. Treatment did not modify the glucose:insulin ratio or serum insulin concentrations. In conclusion, administration of metformin allowed the identification of two subsets of PCOS women in whom neuroendocrine abnormalities may improve independently of the presence of insulin resistance or hyperinsulinaemia.