Increase In LH Pulse Amplitude Research Articles

Reproductive neuroendocrine defects programmed by prenatal testosterone treatment between gestational days 60-90 are amplified by postnatal obesity in sheep.

Polycystic ovary syndrome (PCOS) is the leading cause of anovulatory infertility in women of reproductive age, and obesity can increase the severity and development of the PCOS phenotype. Prenatal testosterone (T) treatment between gestational days 30-90 advanced puberty and disrupted the reproductive and metabolic phenotype in female sheep, recapitulating attributes of women with PCOS, with postnatal obesity amplifying its severity. On the other hand, prenatal T treatment from gestational days 60-90 led to a much milder phenotype. We hypothesized that reproductive neuroendocrine defects programmed by prenatal T treatment between gestational days 60-90 are amplified by postnatal obesity in sheep. Suffolk ewes received T propionate (T; 100mg) or corn oil (C; vehicle) twice weekly from gestational days 60-90. At 5months of age, T lambs were assigned to either a maintenance (100% of NRC requirements) or overfed (130% NRC) diet and C lambs were fed the maintenance diet. We compared the timing of puberty (n = 15/group) determined by twice weekly measurement of progesterone concentrations, estradiol positive feedback responsiveness (n = 8/group) determined by assessing LH secretion in response to exogenous estradiol, periovulatory LH dynamics during the second breeding season (n = 8/group) following synchronization with two injections of PGF2α, and progesterone negative feedback (n = 8/group) determined by characterizing LH pulses during the mid-luteal phase between C, T-maintenance and T-overfed groups. Our findings indicate that postnatal obesity: 1) exacerbated reproductive defects and further deteriorated reproductive cyclicity during the second breeding season (adulthood); 2) did not amplify the impairment in estradiol positive feedback in delaying the timing and amplitude of the LH surge, although it reduced the total amount of LH secreted during the preovulatory LH surge; 3) amplified the reduced responsiveness to progesterone negative feedback manifested as an increase in LH pulse amplitude and peak. These observations, in addition to supporting our previous findings that prenatal T treatment results in reproductive neuroendocrine dysfunction and periovulatory disruptions, provide evidence that these neuroendocrine defects programmed between gestational days 60-90 are amplified by postnatal obesity in female sheep.

Regulation of gonadotrophin-releasing hormone secretion by testosterone in male sheep

In males, including the ram, testosterone, acting via its primary metabolites oestradiol and dihydrotestosterone (DHT), suppresses circulating LH concentrations. This effect is due primarily, although not totally, to decreased frequency of gonadotrophin-releasing hormone (GnRH) pulses. The arcuate-ventromedial region (ARC-VMR) of the mediobasal hypothalamus and possibly the medial preoptic area (mPOA) are sites at which oestradiol acts to suppress GnRH, but the site of DHT action is not known. Given that native GnRH neurones appear to contain few or no oestrogen or androgen receptors, the effects of testosterone metabolites probably are exerted by modulating activity of inhibitory interneurone systems such as beta-endorphin, dopamine, and gamma-aminobutyric acid (GABA). Although beta-endorphin clearly inhibits GnRH secretion, the observation that testosterone treatment during a long-day photoperiod reduced proopiomelanocortin (POMC) mRNA in the arcuate nucleus while coincidentally suppressing GnRH release indicates that beta-endorphin does not mediate the inhibitory effect of testosterone on GnRH. Activation of GABAA receptors in either the mPOA or ARC-VMR suppressed LH, whereas activation of GABAB receptors in the ARC-VMR increased LH pulse amplitude. Therefore, it is suggested that GABA acts in both regions to regulate LH. Whereas testosterone affects GABA metabolism in the rat hypothalamus, its effect in the ram hypothalamus is yet to be determined. Testosterone treatment activated dopaminergic cells in the retrochiasmatic A15 area in the same animals in which it suppressed POMC mRNA in the arcuate nucleus. This dopaminergic system may partially mediate the negative feedback effect of testosterone in the ram analogous to its role in partially mediating the negative effect of oestrogen in the ewe. Future studies must concentrate on determining how these and other putative inhibitory neuronal systems interact and how they in turn are regulated by environmental factors such as photoperiod.

Estradiol Priming Improves Gonadotrope Sensitivity and Pro-Inflammatory Cytokines in Obese Women.

Obesity is associated with a pro-inflammatory state and relative hypogonadotropic hypogonadism. Estrogen (E2) is a potential link between these phenomena because it exhibits negative feedback on gonadotropin secretion and also inhibits production of pro-inflammatory cytokines. We sought to examine the effect of estrogen priming on the hypothalamic-pituitary-ovarian axis in obesity. This was an interventional study at an academic center of 11 obese and 10 normal-weight (NW) women. A frequent blood-sampling study and one month of daily urinary collection were performed before and after administration of transdermal estradiol 0.1 mg/d for one entire menstrual cycle. Serum LH and FSH before and after GnRH stimulation, and urinary estrogen and progesterone metabolites were measured. E2 increased LH pulse amplitude and FSH response to GnRH (P = .048, and P < .03, respectively) in obese but not NW women. After E2 priming, ovulatory obese but not NW women had a 25% increase in luteal progesterone (P = .01). Obese women had significantly higher baseline IL-6, IL-10, TGF-β, and IL-12 compared with NW (all P < .05); these levels were reduced after E2 (-6% for IL-1β, -21% for IL-8, -5% for TGF-β, -5% for IL-12; all P < .05) in obese but not in NW women. E2 priming seems to improve hypothalamic-pituitary-ovarian axis function and systemic inflammation in ovulatory, obese women. Reducing chronic inflammation at the pituitary level may decrease the burden of obesity on fertility.

Developmental Programming: Impact of Prenatal Bisphenol-A on Estradiol Negative Feedback in Sheep.

Endocrine disruptors are hormonally active substances that impact the trajectory of the developing fetus/offspring. An NHANES study found that 99% of humans studied had measurable urinary levels of bisphenol-A (BPA), a chemical with steroidogenic potential used in the plastic industry. Developmental exposure to BPA leads to detrimental effects at several levels including the reproductive axis. In sheep, prenatal exposure to BPA dampens ovulatory LH surges and induces LH hypersecretion. This study tested the hypothesis that LH hypersecretion in prenatal BPA-treated females is the consequence of reduced sensitivity to estrogen negative feedback. A dose response study was conducted involving 4 groups: control (C; n=7), BPA 0.05 mg/kg/day (B1; n=8), 0.5 mg/kg/day (B2; n=8), and 5 mg/kg/day (B3; n=7). Pregnant sheep were treated daily with BPA (in corn oil, s.c.) from days 30 to 90 of gestation. Controls received corn oil. Sensitivity to estrogen negative feedback was tested in all female offspring at ~12 weeks of age. All animals were administered a GnRH antagonist (acycline, 10 μg/kg, s.c.) every 12 h for 72 h to arrest follicular growth and suppress endogenous estradiol production. Eighty hours after cessation of acyline treatment, animals were implanted with a 3 mm Silastic implant containing estradiol (produces prepubertal levels of estradiol). Blood samples were collected at 20 min intervals for 6 h before, at the end of, and 72 h after cessation of GnRH antagonist treatment, and 67 h after insertion of estradiol implant for measurement of LH. LH pulses were detected by cluster algorithm. To test negative feedback effects of estradiol on LH pulse dynamics (frequency, amplitude, and area under the pulse), a paired t-test was used for all LH pulse variables to compare both pre- and post- estradiol periods. To assess BPA dose response relationship, the delta change between pre- and post- estradiol periods was subjected to regression analyses. GnRH antagonist treatment ablated LH pulsatility in all females. Cessation of GnRH antagonist treatment induced high frequency LH pulses in all groups. In controls, estradiol treatment suppressed LH pulse frequency 61.7±10.3% (P<0.01) and increased LH pulse amplitude and area under the pulse 152.2±65.2% (P<0.01) and 440.0±153.8% (P<0.05), respectively. Estradiol treatment also suppressed LH pulse frequency (B1: 45.2±10.1, B2: 48.3±7.2, B3: 66.1±8.8%) and increased LH pulse amplitude (B1: 200.4±34.9, B2: 157.1±38.7, B3: 302.2±101.9%), and area under the pulse (B1: 470.3±60.1, B2: 280.4±64.9, B3: 808.9±232.7%) in all 3 BPA-treated groups (P<0.01 for all doses and variables). The high degree of variability (P<0.05, homogeneity test) found within each BPA dose group, in response parameters, resulted in lack of BPA effect on LH pulse frequency and amplitude. Regression analysis uncovered a significant, but subtle positive linear correlation between BPA dose and area under the pulse (adjusted r2=0.140, P<0.05). In summary, reduced sensitivity to estradiol negative feedback, manifested as increased LH released per pulse, may be a contributing factor to the LH hypersecretion seen in these animals. The high variability in response parameters indicate that the organizational program involved in establishing sensitivity to steroid feedback is the result of the interplay between individual genetic susceptibility and developmental insults. Supported by NIH ES016541.

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.

Histological and steroidogenic changes in dominant ovarian follicles during oestradiol-induced atresia in heifers

Histological and steroidogenic changes within dominant ovarian follicles (DFs) undergoing atresia following systemic administration of oestradiol benzoate (ODB) were characterized in beef heifers. At 5.6+/-0.1 days after the onset of oestrus, heifers received 1 mg ODB i.m./500 kg body weight (ODB; n=15) or served as controls (n=15). Timing of treatment initiation was designated as hour (h) 0 on day (d) 0, and coincided with the presence of the DF of the first follicular wave (DF1). Within treatments, the DF1 was collected following ovariectomy in four animals at h 12, h 36 or after ultrasonic detection of a new wave (NW) of ovarian follicular development. In heifers of the NW groups (n=7 per treatment), blood samples were collected at intervals of 20 min for 12 h beginning at h-12, 0, 24 and 48 to characterize circulating LH patterns. Administration of ODB suppressed (P<0.01) mean concentrations of LH at h 24 and h 48 by preventing (P<0.05) the increase in LH pulse amplitude observed in controls, but had no effect on FSH. Follicular fluid (FF) concentrations of androgens and oestradiol were reduced at h 36 in the ODB-treated group. The diameter of the DF1 and the number of granulosa cell layers were also reduced in ODB-treated as compared with control heifers. Treatment differences were not observed in the proportion of apoptotic granulosa cells as assessed using the TUNEL assay method, and timing of a new wave of follicular development (d 4.6+/-0.2) was similar (P>0.1) among treatments. A prominent characteristic of oestradiol-induced atresia of the DF1 of the oestrous cycle in heifers was a loss in oestrogenic function associated with reduced LH support. However, the timing of new follicular development may be influenced by a factor(s) other than the status of the DF undergoing oestradiol-induced atresia.

Interactions of photoperiod, testosterone, and naloxone on GnRH and LH pulse parameters in the male sheep☆

This study tested the hypothesis that the effects of the opiate antagonist naloxone on GnRH (and LH) secretion is affected by photoperiod length and testosterone (T) concentrations. The effect of infusing naloxone on GnRH and LH pulse patterns was determined in four groups of orchidectomized sheep: long day (LD) photoperiod treated with T, LD without T (LDC), short day photoperiod (SD) with T, SDC ( n = 5–7/group). Hypophyseal-portal and jugular blood samples were collected at 10 min intervals for 4 h before and 4 h during naloxone infusion (1 mg/kg/h). Neither photoperiod nor T affected either mean GnRH or LH whereas naloxone (P < 0.01) increased both. LD photoperiod (P < 0.01), T (P < 0.01) and naloxone (P < 0.01) all increased LH pulse amplitude whereas only naloxone increased GnRH pulse amplitude (P < 0.01). There was an interaction (P < 0.01) between steroid and naloxone on LH, but not GnRH, pulse amplitude. Both LD photoperiod and T increased both LH and GnRH (P < 0.01) interpulse-interval (IPI). Naloxone decreased GnRH IPI (P < 0.01). The LH/GnRH pulse amplitude ratio was (P < 0.02) increased by T—likely a secondary response to the T-induced increase in IPI. These results are interpreted as showing that in the ram the endogenous opiate peptides regulate both GnRH pulse frequency and amplitude, but that their specific role is modulated by photoperiod and T. These results do not support the concept that the opiate peptides are the primary mediators of the negative feedback effects of T.

Changes in androgen secretion and luteinizing hormone pulse amplitude are associated with the recruitment and growth of ovarian follicles during the luteal phase of the bovine estrous cycle.

In cattle the development of large antral follicles occurs in two or three successive waves during the estrous cycle, with one follicle per wave selected for dominance. To test the hypothesis that negative feedback effects of steroids secreted by the dominant follicle are critical to the regulation of follicular waves, we examined temporal relationships among ovarian follicular growth, steroid secretion, and gonadotropin secretion. Follicular growth was monitored by ultrasonography. In the first experiment, blood was collected from 5 Holstein heifers every 8 h between Days 0 and 14 of the estrous cycle from both a jugular vein and the vena cava (to collect ovarian blood). Jugular samples were also collected every 12 min for 8 h during three periods (Days 3 or 4, 7 or 8, and 11, 12, or 13; n = 6) to characterize the pulsatile pattern of LH secretion. Both estradiol and testosterone concentrations in the vena cava increased as pre-wave elevations in FSH concentrations decreased (p < 0.05) between Days 1 and 4 (first follicular wave) and between Days 9 and 12 (second follicular wave). LH pulse amplitude was greater during the second period of frequent blood collection (Day 7 or 8, end of the growth phase of the first dominant follicle) compared to the other two periods (p < 0.05), suggesting that increased LH pulse amplitude may be important for the later stages of dominant follicle growth. In the second experiment, to determine whether ovarian steroids are secreted primarily by dominant follicles, blood samples were collected from the utero-ovarian veins draining ovaries with (n = 4) and without (n = 4) a dominant follicle during the first follicular wave. Testosterone, androstenedione, and estradiol concentrations in the utero-ovarian veins fluctuated in relation to the pattern of follicular growth (p < 0.05), and secretion was much greater from ovaries with a dominant follicle. In blood collected both from the vena cava and from the utero-ovarian veins, estradiol secretion reached a peak and started to decline before androgen concentrations peaked (p < 0.05), suggesting that the initial decrease in estradiol secretion from the dominant follicle is not due to a lack of androgen precursors. The results suggest that 1) a transient increase in LH pulse amplitude during the early-midluteal phase may be important for supporting the final stages of dominant follicle growth; 2) ovarian androgens, as well as estradiol, may play a critical role in the control of FSH secretion during waves of follicular development; and 3) the dominant follicle is responsible for fluctuations in circulating estradiol and androgens during follicular waves.

Development of the hypothalamic-pituitary-ovarian axis.

The onset of puberty is a centrally driven process, the detailed mechanisms of which are not known. It is translated into an increased activity of the hypothalamic GnRH pulse generator. This in turn is seen as increased pituitary pulsatile secretion of LH and FSH. LH pulses are observed even in midchildhood, particularly after the onset of sleep. Onset of puberty is associated with a greater increase in LH pulse amplitude than frequency and a much greater increase in LH and FSH. A progressive increase in daytime pulsatility occurs, with a gradual reduction of sleep-entrained amplification. Prepubertal FSH concentrations are relatively high in girls, and continous ovarian follicular growth and atresia take place, with estradiol concentrations being higher than in boys. Only after the steep early pubertal increase in LH, ovarian steroidogenesis is activated, with increases in androgen and estrogen secretion. Under further FSH stimulation, follicular growth and maturation proceed. The first menstrual cycles are mostly anovulatory for 1 to 2 years. Luteal phase insufficiency is common the first five years after menarche.

Comparison of the neuroendocrine control of pubertal maturation in girls and boys with spontaneous puberty and in hypogonadal girls.

Puberty in boys is characterized by a nocturnal increase in mean LH concentration and LH pulse frequency. To determine whether similar mechanisms exist in girls, nocturnal serum LH concentrations were determined in 16 girls with constitutional delay of adolescence or idiopathic short stature who had or have subsequently been shown to have spontaneous puberty. Mean LH and LH pulse frequency and amplitude were analyzed in 3-h blocks and compared to those in 20 pubertal boys. Girls had an increase in mean LH concentration from 3.6 +/- 0.7 IU/L at 2000-2250 h to 4.8 +/- 0.9 IU/L at 0200-0450 h. LH pulse frequency increased from 0.27 +/- 0.11 pulses/girl.h at 2000-2250 h to 0.54 +/- 0.10 pulses/girl.h at 0200-0450 h. The increase in LH pulse amplitude, from 2.0 +/- 0.8 IU/L at 2000-2250 h to 4.1 +/- 1.1 IU/L at 2300-0150 h, did not achieve statistical significance because many girls had no pulses from 2000-2250 h. With advancing age, the day/night differences in LH concentration and LH pulse frequency disappeared in girls, but were preserved in boys of same pubertal stage. The effect of lack of estrogen on LH pulse characteristics was inferred by analyzing the LH profiles of 15 girls with gonadal dysgenesis who were age-matched to girls with spontaneous puberty. The girls with gonadal dysgenesis had an increase in mean LH concentration after 0200 h, but LH pulse frequency was rapid in all time blocks; the nocturnal increase in LH concentration was secondary to a significant increase in LH pulse amplitude. Older girls with gonadal dysgenesis had a loss of nighttime augmentation of LH secretion similar to that seen in girls with spontaneous puberty. These data suggest that the apparent slower LH pulse frequency encountered in girls with spontaneous puberty during waking hours may be related to estrogen suppression of LH pulse amplitude, which masks the true daytime LH pulse frequency. With or without pubertal estrogen exposure, developmental progression of LH secretion occurs more rapidly in girls than in boys. Thus, intrinsic sex differences exist in the timing and tempo of endocrine control of pubertal maturation between boys and girls.

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.

Effects of follicular phase exercise on luteinizing hormone pulse characteristics in sedentary eumenorrhoeic women

Current studies reveal little regarding the inception of exercise-induced LH changes during physical training. This study aimed to assess the susceptibility of the hypothalamic-pituitary axis to the acute physical stress of exercise in untrained, physically inactive women. The acute effects of submaximal endurance exercise upon the pulsatile LH secretion in the follicular phase were compared with those accompanying leisurely strolling for a similar time period. All subjects were eumenorrhoeic, as determined by biphasic temperature patterns, detection of the urinary LH surge, and mid-luteal serum progesterone levels. Subjects were not physically active and had little history of strenuous exercise (VO2max = 38.0 +/- 1.8) (mean +/- SEM) ml/kg/min). All women completed a 13.5-hour pulsatility test which included three consecutive 20-minute runs on a treadmill at 50, 60 and 70% of the subjects' maximum oxygen uptake (n = 16). Six of these same subjects completed a separate test on another occasion in which one hour of leisurely strolling was substituted for exercise. Blood was sampled every 10 minutes via an indwelling cannula for 4.5 hours before and 8 hours after one hour of exercise and or strolling. A pulse algorithm (Pulsar) was used to quantify LH pulse characteristics. Exercise produced no significant effects upon LH pulse frequency or mean serum LH concentration. However, exercise of moderate intensity caused a significant increase in LH pulse amplitude (P < 0.05). Strolling produced no significant changes in LH secretion. Acute exercise of moderate intensity in the follicular phase of untrained women is an insufficient stimulus to inhibit the GnRH pulse generator in the post-exercise period, yet may produce a slight stimulatory effect on the amount of LH released per pulse.

Gonadotropin-releasing hormone pulse generator activity during pubertal transition in girls: pulsatile and diurnal patterns of circulating gonadotropins.

To delineate the activity of the GnRH pulse generator during pubertal transition, 40 healthy girls 7-18 yr of age were studied. Ten were prepubertal (PP), 7 were in early puberty (EP), and 23 were in late puberty (LP, all postmenarcheal). Serum concentrations of LH and FSH were measured with immunofluorometric assays, which have a sensitivity about 100-fold that of RIA, in samples taken at 10-min intervals for 24 h during basal conditions, during Nal-Glu antagonist suppression, and in response to GnRH stimulation (10 micrograms). Serum levels of androstenedione, testosterone, and estradiol were measured with RIA. A pulsatile pattern of LH and FSH secretion was found in girls of all ages. PP girls had irregular LH pulses with low amplitudes during the daytime, but increased amplitude LH and FSH pulses were evident within 1 h after sleep-onset. Older PP girls had more regular and higher amplitude pulses throughout sleep than younger PP girls. The sleep-related LH and FSH pulses in PP girls were abolished with Nal-Glu GnRH antagonist treatment, reflecting endogenous GnRH pulse activities. The PP group had the most pronounced amplification of LH secretion with sleep yielding a sleep-wake ratio of 4, which decreased to 2 in the EP group and to 1 in the LP group. The emergence of regular daytime LH pulses along with a further amplification of pulsatile activity during sleep was closely related to the onset of breast development. By the age of 16 yr, an LH secretory pattern characteristic of adult women in the early follicular phase, i.e. a decrease in LH concentration during sleep, was established. Mean 24-h LH concentrations increased 40-fold from PP to LP consequent to a 9-fold increase in pulse amplitude and a 4-fold increase in pulse number (both P < 0.0001). Mean FSH concentrations (24 h), which were 20-fold higher than corresponding LH concentrations in the PP group, increased only 3-fold from the PP to the LP group. FSH pulse secretion appears to be predominantly GnRH dependent in PP girls in contrast to girls after ovarian activation, as indicated by the increased FSH responses to both GnRH antagonist suppression and GnRH stimulation in the PP as compared to the EP and LP groups. We conclude that the GnRH pulse generator is functionally active in prepubertal girls with selective expression of LH and FSH pulses after the onset of sleep. The onset of puberty is associated with a greater increase in LH pulse amplitude than frequency.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition of Endogenous Catecholamine Synthesis Augments Early Follicular Phase Luteinizing Hormone Secretion*

The physiological role of catecholamines, particularly dopamine and norepinephrine, in the regulation of gonadotropin secretion in humans is unclear. We administered the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine (AMPT, 500 mg at 800 and 1000 h) to five women in the early follicular phase of the menstrual cycle and compared LH secretion patterns to those in five untreated controls. Commencing at 800 h, blood was drawn every 15 min for LH and PRL measurements until 1600 h. AMPT elevated PRL concentrations (mean +/- SEM) from a baseline of 14.72 +/- 2.51 micrograms/L to a peak of 102.2 +/- 24 micrograms/L. LH concentrations [21.97 +/- 0.56 (AMPT) vs. 13.51 +/- 0.16 IU/L (control), P less than 0.0001], LH area under the curve [11014 +/- 1815 (AMPT) vs. 7009 +/- 404 IU.min/L (control), P = 0.05] and LH pulse amplitude [9.99 +/- 2.38 (AMPT) vs. 4.03 +/- 0.61 IU/L (control), P = 0.04] were all greater in the group in which catecholamine synthesis was inhibited. There was no difference in pulse frequency between the groups (7.4 +/- 0.51 vs. 6.6 +/- 0.24 pulses/8 h, P greater than 0.05). We conclude 1) inhibition of endogenous catecholamine synthesis augments LH levels in the early follicular phase, and 2) increased LH secretion during catecholamine synthesis inhibition is due, at least in part, to increased LH pulse amplitude but not increased LH pulse frequency.

Acetyl‐1‐carnitine as possible drug in the treatment of hypothalamic amenorrhea

Several neuroendocrine disregulations have been demonstrated in patients with hypothalamic amenorrhea, but a definite therapeutic strategy has not yet been found. Since acetyl-l-carnitine (ALC) has been reported to have a specific effect on central cholinergic, serotoninergic, dopaminergic and opioidergic systems, 20 patients with hypothalamic amenorrhea were treated with ALC (2 g/day, per os). Both the clinical efficacy and the endocrine parameters were evaluated after 6 months. The patients were subdivided in two groups according to their LH plasma levels: A) hypogonadotropic: 10 subjects with plasma LH less than 3 mIU/ml, and B) normogonadotropic: 10 subjects with plasma LH greater than 3 mIU/ml. All subjects underwent: 1) a pulsatility study (4 h sampling every 10 min), 2) GnRH test (two bolus injections of 10 micrograms at time 0 and +120), 3) TRH test (200 micrograms). These parameters were evaluated before and after 6 months of ALC administration. The occurrence of a spontaneous menstruation was observed in 6 out of 10 hypogonadotropinemic and in 4 out of 10 normogonadotropinemic patients. Menstrual bleeding occurred between the 3rd and the 6th month of therapy. Major hormonal changes after ALC administration were observed in the hypogonadotropic subjects. They showed a significant increase in baseline plasma LH levels (from 0.9 +/- 0.1 to 3.5 +/- 0.7 mIU/ml, p less than 0.05) (mean +/- SEM), a significant increase in LH pulse amplitude (p less than 0.01) with no changes in LH pulse frequency, and a significantly increased response of LH to the latter GnRH bolus during the GnRH test. Hypogonadotropic patients also showed a significant increase in both estradiol (from 18.8 +/- 2.5 to 48 +/- 3.3 pg/ml, p less than 0.05) and PRL (from 6 +/- 1 to 11.4 +/- 1.7 ng/ml, p less than 0.05). No significant differences were observed in the hormonal parameters of normogonadotropic patients after 6 months of ALC therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulsatile secretion of LH during the periovulatory and luteal phases of the oestrous cycle in the Pere David's deer hind (Elaphurus davidianus)

Changes in the secretion of LH during the oestrous cycle were studied in 5 tame Père David's deer in which ovulation was synchronized with progesterone implants and prostaglandin injections. Plasma LH concentrations were measured in samples collected at 15-min intervals for a 36-h period, starting 16 h after the removal of the progesterone implants (follicular phase), and for a further 10-h period 10 days after the removal of the progesterone implants (luteal phase). In all animals, there was a preovulatory surge of LH and behavioural oestrus which occurred at a mean time of 59.6 h (+/- 3.25) and 69 h respectively following implant removal. LH pulse frequency was significantly higher during the follicular phase (0.59 +/- 0.03 pulses/h) than the luteal phase (0.24 +/- 0.2 pulses/h), thus confirming in deer findings from research on domesticated ruminants. There were no significant differences between the follicular and luteal phases in mean plasma LH concentrations (0.57 +/- 0.09 and 0.74 +/- 0.13 ng/ml) or mean pulse amplitude (0.99 +/- 0.14 and 1.05 +/- 0.21 ng/ml) for the follicular and luteal phase respectively. The long interval from the removal of progesterone to the onset of the LH surge and the absence of a significant difference in mean LH concentration or pulse amplitude in the follicular and luteal phases resemble published data for cattle but differ from sheep in which there is a short interval from luteal regression to the onset of the surge and a marked increase in LH pulse amplitude during the luteal phase.

LH pulsatility and response to a single s.c. injection of buserelin in polycystic ovary syndrome

The present study was undertaken in order to determine whether patients with polycystic ovary syndrome (PCOS) have LH pulse frequency and/or amplitude higher than those in normal cycling women during the follicular phase, and, if so, to establish possible factors which might influence LH secretion in PCOS. The study was conducted on 14 PCO patients (aged 19-30 years), who were subdivided according to the data on their cycle abnormality into 2 groups: amenorrheic (Am-PCOS, n = 9) and oligomenorrheic (O-PCOS, n = 5). LH pulsatility was assessed in the early follicular phase in controls (n = 5) and O-PCOS and at any time in Am-PCOS. Blood samples were taken every 10 minutes for 4 hours. Pulse analyses of LH data were performed using the Munro program. The buserelin test was performed on the same day by injection of 40 micrograms of buserelin (blood samples were taken every 60 minutes for the following 10 hours). Eleven PCO patients and 12 control subjects had an oral glucose tolerance test (oGTT) (blood samples were taken every 60 minutes for glucose, insulin and C-peptide measurements). Both mean LH pulse frequency and mean pulse intervals were not distinguishably different in PCO women (Am and O) and controls. In contrast, the mean pulse amplitude was significantly higher in the Am-PCOS group than in O-PCOS women and controls (p less than 0.02 and p less than 0.001, respectively). A significant positive correlation was established between nadir LH concentrations and LH pulse amplitude (r = +0.966, p less than 0.001). The LH response to buserelin stimulation was significantly higher in Am-PCOS than in O-PCOS (p less than 0.004). A highly significant positive correlation was observed between LH pulse amplitude and insulin response during oGTT (p less than 0.001) in PCO subjects. Basal (prebuserelin) LH concentrations correlated significantly with fasting insulin levels (p less than 0.008) and insulin and C-peptide responses to oGTT. These results allow us to conclude the following: 1. An increased LH pulse amplitude and an exaggerated LH response to buserelin observed in amenorrheic PCO subjects compared to those in oligomenorrheic PCO subjects fail to support the hypothesis of an intrinsic hypothalamo-pituitary abnormality. 2. The relationship between fasting and glucose-stimulated insulin levels with LH nadir concentrations, pulse amplitude and response to buserelin suggests an etiological role of insulin in the pathogenesis of PCOS.

LHRH pulse frequency in normal and infertile men

The aim of this study was to examine the hypothesis that decreased LHRH pulse frequency may be responsible for the preferential rise in FSH in infertile men. The LH pulse pattern was determined as an index of hypothalamic LHRH secretion in 21 infertile patients with idiopathic azoospermia or oligoasthenozoospermia and 14 fertile age-matched controls by frequent blood sampling at 10-min intervals for 24 h. The infertile patients were further divided into three groups according to their relative concentrations of FSH and LH: (1) normal FSH and LH, (2) raised FSH but normal LH, and (3) raised FSH and LH. LH pulses were detected by a computerized algorithm (Munro) validated against a threshold method. Concentrations of FSH, testosterone, sex hormone-binding globulin and oestradiol were measured in pooled plasma. Luteinizing hormone pulse frequencies in normal men were not significantly different from the infertile group as a whole. Similarly, mean LH pulse frequencies in infertile subgroups 1, 2 and 3 were not significantly lower than normal. Pulse interval, however, was increased in subgroup 1 compared with normal. Mean 24 h LH in group 2 was significantly higher than normal, but still within the normal range. The total testosterone, but not the free testosterone index was significantly decreased in the infertile group compared with normal. There was no correlation between mean FSH and LH pulse frequency or interval. In conclusion, our results show that in patients with seminiferous tubular dysfunction, the typical pattern of raised plasma FSH, increased LH pulse amplitude, raised FSH: LH ratio and normal or marginally low testosterone was not associated with any significant deviations in LHRH pulse frequency from the range observed in normal fertile men. This is not compatible with the hypothesis that decreased LHRH pulse frequency is associated with or the cause of the preferential rise in FSH in men with idiopathic infertility. Thus unlike anovulatory infertility in females, functional defects of hypothalamic LHRH secretion remain an uncommon finding in male infertility. Attempts to treat idiopathic oligozoospermia by altering LHRH pulse frequency is therefore unlikely to yield any clinical benefit.

Role of endogenous opioid peptides in the initiation of the midcycle luteinizing hormone surge in normal cycling women.

While compelling evidence indicates a pivotal role for endogenous opioids in the regulation of GnRH-LH pulsatile activity during the late follicular and luteal phases of the menstrual cycle, the participation, if any, of the opioidergic mechanism in the initiation of the midcycle surge has not been examined. Accordingly, we measured serum LH, FSH, estradiol (E2) and progesterone (P4) levels daily during 2 consecutive cycles in 12 normal cycling women. After a control cycle, each woman was infused with naloxone (30 micrograms/kg.h) for 24 h starting 3 days before the anticipated spontaneous midcycle surge. Blood samples were obtained at 15-min intervals for 8 h before, during, and 16 h after the naloxone infusion. Serum LH and FSH concentrations were measured in all samples, and serum E2 and P4 concentrations at 2-h intervals. Pulsatile LH secretion was analyzed using the cluster program. The opioidergic blockade elicited a robust increase in LH pulsatile activity and a 3-fold rise in serum FSH levels in 6 of the 12 women. This increased gonadotropin secretion lasted more than 24 h and was characterized by a progressive increase in LH pulse amplitude, which was 9-fold greater during the last 8 h of naloxone infusion [mean LH pulse amplitude, 36.5 +/- 4.5 (+/- SE) vs. 4.1 +/- 0.4 IU/L; P less than 0.001]. This increase was accompanied by a corresponding increase in transverse mean serum LH levels (83.3 +/- 13 vs. 20.7 +/- 3.2 IU/L; P less than 0.001), but no alteration of the interpulse interval (93 +/- 11 vs. 85 +/- 4 min). The peak serum LH concentrations exceeded 100 IU/L in all 6 of these women. This naloxone-advanced gonadotropin surge, resembling closely the spontaneous midcycle surge, resulted in a significantly shortened (P less than 0.001) follicular phase and a more than 2-fold elevation of serum P4, followed by assumed ovulation and normal luteal function. These 6 women had serum E2 levels immediately before naloxone infusion that were comparable to those during the preovulatory peak during the control cycle. In the 6 women who did not have a naloxone-induced increase in gonadotropin secretion the preinfusion serum E2 levels were substantially lower (P less than 0.001) than the values during the control cycle. These findings suggest that a transient decrease in opioidergic activity may contribute to the initiation of the midcycle gonadotropin surge in women.

Effects of adrenalectomy on photoperiod-induced changes in release of luteinizing hormone and prolactin in ovariectomized ewes.

Finnish Landrace x Southdown ewes were ovariectomized (OVX) and subjected to daily photoperiods of 16L:8D (Group I) or 8L:16D (Group II) for 84 days. Ewes were then either adrenalectomized (ADX) (N = 5 for Group I; N = 4 for Group II) or sham ADX (N = 6 for Groups I + II). After surgery, ewes in Group I were subjected to 8L:16D for 91 days and 16L:8D for 91 days whereas ewes in Group II were exposed to 16L:8D for 91 days and 8L:16D for 91 days. Oestradiol implants were inserted into all ewes on Day 148. Sequential blood samples were taken at 28, 56, 91, 119, 147 and 168 days after surgery to determine secretory profiles of LH and prolactin. Photoperiod did not influence LH release in Group I in the absence of oestradiol. Although photoperiod influenced frequency and amplitude of LH pulses in Group II before oestradiol treatment, adrenalectomy did not prevent these changes in patterns of LH release. However, in Group II the increase in LH pulse amplitude during exposure to long days was greater (P less than 0.01) in adrenalectomized ewes than in sham-operated ewes. Mean concentrations of LH increased in ADX ewes on Days 91 (P = 0.07) and 119 (P less than 0.05). Adrenalectomy failed to influence photoperiod-induced changes in mean concentrations of LH, amplitude of LH pulses and frequency of LH pulses in the presence of oestradiol. Concentrations of prolactin were influenced by photoperiod. In Groups I and II concentrations of prolactin increased (P less than 0.01) after adrenalectomy, but the magnitude of this effect decreased over time.(ABSTRACT TRUNCATED AT 250 WORDS)