FSH Pulse Amplitude Research Articles

Temporality of ovarian steroids and LH/FSH pulse profiles encompassing selection of the dominant follicle in heifers†.

The tested hypotheses were (1) LH/FSH pulses and F2 diameter are diminished by P4 and, (2) E2 increases during the transition to deviation and alters LH/FSH pulses. On Day 5 (Day 0 = ovulation), heifers were randomized into an untreated group (HiP4, n = 11), and a prostaglandin analog treated group (NoP4, n = 10). On Day 6, a follicular wave was induced by follicle ablation. Ultrasound and blood collections were performed every 12h from Days 7 to 11. Blood was collected every 15min for 10h on Day 9 (largest follicle expected to be ~7.5mm). Estradiol was ~75% greater (0.36 ± 0.14 vs 0.63 ± 0.19pg/mL) in heifers with F1 ≥ 7.2mm than in heifers with F1 < 7.2mm. The HiP4 had smaller second largest follicle (F2) diameter, lower estradiol (P = 0.06), LH pulse baseline and peak concentrations (P < 0.007), in addition to half the frequency of LH/FSH pulses (4.1 ± 0.3 vs 9.6 ± 0.7 in 10h) than the NoP4. Within HiP4, heifers with F1 ≥ 7.2mm had ~25% fewer (P = 0.03) LH pulses compared to heifers with F1 < 7.2mm. In contrast, within the NoP4, heifers with F1 ≥ 7.2mm had ~75% greater LH (P = 0.05) and FSH (P = 0.08) pulse amplitude. We propose that greater F2 diameter at deviation in low P4 is related to greater LH baseline and peak concentrations, and greater frequency of LH/FSH pulses. A greater increase in E2 after F1 reaches ~7.2mm results in further stimulation of LH/FSH pulse amplitude. Elevated P4 not only diminished frequency of LH/FSH pulses but also converted an E2 increase into a negative feedback effect on LH/FSH pulse frequency leading to smaller F2 at deviation.

Análogo de GnRH disminuye la secreción de hormona folículo estimulante (FSH) en ovejas prepúberes

SUMMARY LH and FSH secretions depend on the pulsatile secretion of GnRH from the hypothalamus. However, the grade of dependency as well as the relationship between pulses of GnRH and pulses of FSH secretion is less clear. Experiments in monkeys have shown that high GnRH pulse frequency favors LH secretion while low frequency of GnRH pulses preferentially stimulates the FSH secretion. The objective of the present work was to recognize the dependence of GnRH on the FSH secretion in prepubertal female sheep. A GnRH agonist analogue in slow release microcapsule preparation was used (Trp6-GnRH, (Decapeptyl®)) whose blocking effect on the LH release has been previously demonstrated. The analogue was injected intramuscularly every 4 weeks beginning at 20 weeks of age three times in five Suffolk ewe lambs. Another group of five lambs received the vehicle of Decapeptyl. Studies of FSH pulsatility were carried out at 20 (before the analogue agonist administration), 26 and 30 weeks of age. The CLUSTER program was used to identify characteristics of FSH secretion: transversal mean (ng/ml/5h), frequency of pulses (number of pulses/5h), amplitude of pulses (ng/ml) and nadir (ng/ml) . In the control group, FSH secretion characteristics did not change between 20 and 30 weeks of age. In the experimental group, mean FSH concentrations decreased from 3.4±0.3 ng/ml/5h at 20 weeks of age to 0.36 ±0.1 ng/mL/ 5h at 30 weeks of age (P<0,05), which was also significantly lower than in the control group of the same age. Amplitude of FSH pulses in lambs of 30 weeks of age were significantly lower than in lambs of 20 weeks of age (4.4 ± 0.5 versus 0.5 ± 0.1 ng/mL respectively, P<0.05), and lower than that exhibited by control ewe lambs of 30 weeks of age. FSH pulse frequency did not change between lambs of 20 and 30 weeks of age in either group. Results show that the GnRH analogue is able to block the FSH secretion suggesting that the FSH secretion is dependant on GnRH stimulation in prepubertal female sheep.

Elevated FSH concentrations in imminent ovarian failure are associated with higher FSH and LH pulse amplitude and response to GnRH.

Imminent ovarian failure (IOF) in women is characterized by regular menstrual cycles and elevated early follicular phase FSH. This study explored underlying neuroendocrine causes of elevated FSH concentrations on day 3 of the menstrual cycle. The characteristics of episodic secretion of FSH and LH, the pituitary response to gonadotrophin-releasing hormone (GnRH), plasma oestradiol, and dimeric inhibin A and inhibin B on day 3 were compared in 13 women with elevated FSH concentrations (>10 IU/l) and 16 controls. FSH amplitudes were higher in the IOF group than in the controls (P < 0. 0001). The FSH pulse frequency did not differ between groups. The FSH response to GnRH was higher in the IOF patients than in the controls (P < 0.0001). Mean LH, LH amplitude and LH response to GnRH were higher in the IOF group, but LH pulse frequency did not differ between the groups. Concentrations of inhibin A and inhibin B were lower in the IOF group, while oestradiol showed no differences. We concluded that in women with IOF, the pituitary is more sensitive to GnRH. This leads to higher FSH and LH pulse amplitudes which underlie the elevated FSH concentrations in the early follicular phase.

Effects of season of birth on the prepubertal pattern of gonadotropin secretion and age at puberty in beef heifers

There is an early transient rise in gonadotropin secretion in spring-born prepubertal heifers and there is an indication that this pattern is different in autumn-born heifers. The effect of season of birth on age and weight at puberty is equivocal. This study was designed to compare the temporal patterns of LH and FSH secretion between spring- and autumn-born heifers and to determine the effects of season of birth on age and weight at puberty. Blood samples from 2 groups of heifer calves born in spring (last week of March, n = 5) or autumn (last week of October, n = 5) were collected every other week from birth to puberty and every 15 min for 10 h at 6,12,18, 24 and 32 wk of age. Timing of puberty was determined by measuring progesterone in plasma samples collected every 2 to 3 d starting at 42 wk of age. Age and weight at onset of puberty did not differ between the 2 groups of heifers (P > 0.05); however, the autumn-born heifers tended to mature in a wider range of ages and weights. Based on the 10-h sampling periods, mean serum concentrations of LH and LH pulse frequency and amplitude were higher in spring-born heifers at 18 wk of age than in autumnborn heifers (P < 0.05). In spring-born heifers, LH pulse frequency increased over time to 32 wk of age, and LH pulse amplitude was higher at 12 and 18 wk than at 32 wk of age (P < 0.05). Autumnborn heifers had higher LH pulse frequency at 6 wk and showed a decrease in mean concentrations of LH at 12 and 18 wk of age (P < 0.05). The FSH pulse frequency of spring-born heifers was higher at 12 wk of age than in autumn-born heifers (P < 0.05), FSH pulse amplitude in autumn-born heifers decreased from 6 to 32 wk of age. It was concluded that although the mean age and weight at puberty did not differ between spring- and autumn-born heifers, the range in age and weight at puberty was wider in the autumn-born heifers. The patterns of LH secretion differed between spring- and autumnborn prepubertal heifers, with spring-born calves exhibiting an early rise in LH secretion, while mean serum concentrations of LH decreased during this period in autumn-born heifers.

Cocaine impairs follicular phase pulsatile gonadotropin secretion in rhesus monkeys.

To assess cocaine's effect on follicular phase pulsatile gonadotropin secretion in normally cycling rhesus monkeys. Sixteen monkeys were paired by body weight and randomized to receive intravenous saline (n = 8) or cocaine (4 mg/kg, n = 8) daily on cycle days 2 to 14. Monkeys were chronically cannulated to allow frequent blood collections without anesthesia. Blood samples were obtained every 15 minutes for 8 hours in early (EFP; cycle days 1 to 5), mid-(MFP; cycle days 6 to 10), and late (LFP; cycle days 11 to 15) follicular phase. Plasma concentrations of LH, FSH, and estradiol-17 beta (E2) were determined by radioimmunoassay. Pulses were identified by cluster analysis. Statistical differences were determined by analysis of variance (ANOVA) and Sidak's multiple comparison test. Seven out of eight monkeys in the control group demonstrated timely ovulation. Only one monkey in the cocaine-treated group ovulated. Similar gonadotropin pulse intervals (70 to 90 minutes) were observed throughout the follicular phase in both the controls and cocaine-treated monkeys. LH and FSH pulse amplitudes increased significantly from the EFP/MFP to the LFP in controls. In cocaine-treated monkeys, gonadotropin pulse amplitudes remained at EFP/MFP levels throughout the study period. The mean gonadotropin pulse amplitude and the mean E2 levels in the LFP were significantly greater in controls as compared with cocaine-treated monkeys (P < .001). These findings demonstrate that cocaine suppresses the normal increase in LH and FSH pulse amplitude seen in the LFP. Further studies are in progress to determine the mechanism of cocaine's disruption of the hypothalamic-pituitary-ovarian axis.

Gonadotrophin profiles and dioestrous pulsatile release patterns in mares as determined by collection of jugular blood at 4 h intervals throughout an oestrous cycle.

In mares, dioestrous FSH profiles based on once-a-day sampling are variable; however, the pulsatility of plasma FSH, which has been suggested by limited windows of intensive sampling, may contribute to this variability. Jugular blood from six mares was sampled at 4 h intervals throughout an ovulatory cycle to determine cyclic FSH and LH patterns more accurately and to measure gonadotrophin pulse frequency during dioestrus. Synchronous pulses of FSH and LH occurred regularly in all mares between day 4 and day 12 (ovulation = day 0) with a mean (+/- SEM) frequency of 1.9 +/- 0.1 (FSH) or 1.6 +/- 0.1 (LH) pulses day-1. LH pulse amplitude declined (P < 0.0001) between day 4 and day 10, but FSH pulse amplitude remained large and stable, dipping slightly but not significantly on day 6. Daily mean FSH concentrations exceeded (P < 0.0001) early oestrous values between day 4 and day 5, and between day 7 and day 10. However, significantly different patterns were obtained when once-a-day sampling was simulated by selecting samples collected at 08:00 h or noon. LH was higher during the periovulatory surge than during dioestrus (P < 0.0001) and profiles were similar whether daily means or selected samples were used. It is concluded that: (1) the marked pulsatility of plasma FSH during dioestrus makes once-a-day sampling misleading for determining FSH profiles; (2) the dioestrous pattern of large, slow FSH pulses was consistent among mares, unlike that of the daily mean FSH profiles; and (3) no discrete FSH 'surges' were observed during dioestrus, although FSH pulse amplitude tended to undergo alternate increases and decreases. A period of higher amplitude FSH pulses preceded ovulation by 10.2 +/- 0.7 days, which corresponds to the approximate time the ovulatory follicle emerges. Therefore, it is possible that the signal for follicular recruitment in mares is intermittent excursions of plasma FSH above a threshold value.

Increased levels and pulsatility of follicle-stimulating hormone in mothers of hereditary dizygotic twins.

According to the endocrine model of hereditary dizygotic twinning, high FSH is responsible for multiple ovulation and pregnancy. Our study explored the underlying neuroendocrine causes. In a prospective clinical study, we compared the third day of menses parameters of episodic secretion of LH and FSH, the pituitary response to LHRH, plasma estradiol, and dimeric inhibin A and B in 16 regularly menstruating and 9 postmenopausal mothers of dizygotic twins with a family history of twinning and 14 premenopausal and 9 postmenopausal controls. Seven of 16 premenopausal mothers of twins had abnormally high FSH levels of more than 10 IU/L compared with 1/14 in controls (P = 0.024). In the premenopausal mothers of twins, mean FSH concentrations (P = 0.025) and FSH pulse frequency (P = 0.003) were significantly elevated, whereas FSH pulse amplitude and FSH response to LHRH were unaltered. For LH, neither the secretory parameters nor the response to LHRH was different. There were no differences between estradiol and inhibin A and B levels. Postmenopausal mothers of twin and controls did not differ with respect to the secretory pattern of LH and FSH. We conclude that under equal ovarian feedback conditions, premenopausal mothers of a dizygotic twin have hyper stimulation by endogenous FSH caused by neuroendocrine, hypothalamic, or pituitary mechanisms. This is the result of altered responsiveness to ovarian feedback and/or pituitary or suprapituitary, non-LHRH-like mechanisms that stimulate pulsatile FSH.

Effect of inhibition of increased gonadotrophin secretion before 20 weeks of age in bull calves on testicular development.

In bull calves serum concentrations of LH, FSH, and to a lesser extent testosterone, are increased transiently, between 6 and 20 weeks of age. The function of gonadotrophin and testosterone secretion in this period of growth and development was tested by injecting five Hereford bull calves with a GnRH agonist (15 mg Leuprolide acetate) i.m. at 6, 10 and 14 weeks of age; five vehicle treated calves acted as controls. On the basis of blood samples taken every 15 min for 10 h, at 12 weeks of age, mean serum concentrations of LH, FSH and testosterone and LH and FSH pulse frequency and amplitude were decreased (P < 0.05) by Leuprolide acetate. At 24 weeks of age, mean serum concentrations of LH, and LH and FSH pulse frequency in Leuprolide acetate treated calves exceeded (P < 0.05) that seen in control calves. On the basis of blood samples taken every other week, treatment with Leuprolide acetate decreased mean serum concentrations of FSH and testosterone at 14, 16 and 18 weeks of age compared with control calves and delayed the peak of the early increase in LH secretion from 20 to 24 weeks of age (P < 0.05). Scrotal circumference between 22 and 50 weeks of age, pixel units from ultrasound images of the testes, testis mass at castration at 50 weeks of age, and numbers of spermatids and pachytene spermatocytes were all lower in Leuprolide treated calves than in controls. A transient increase in secretion of LH, FSH and testosterone in young bull calves before 20 weeks of age may, therefore, be a critical step in the initiation and timing of testicular development in bull calves.

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.

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.

Periovulatory LH, FSH and steroid hormone profiles in superovulated and unstimulated holstein heifers

Periovulatory gonadotrophin and steroid hormone profiles were compared between superovulated and unstimulated Holstein heifers. Treatment was induced in luteal-phase heifers with 8 injections of FSH (superovulated n=9) or saline (unstimulated n=3) given over 5 d. Both groups received 0.5 mg of cloprostenol (PG) with the sixth injection of FSH or saline to induce luteolysis. All animals were inseminated at estrus, and embryos were collected at Day 7 of gestation. Blood samples were taken hourly for 6 h after the morning injection of FSH (or saline) and then every 15 min for 3 h (from 1400 to 1700 h) on each of the 5 treatment days. Before PG, mean serum progesterone and estradiol concentrations were higher (P ≤ 0.05) and LH pulse frequency and amplitude were lower (P ≤ 0.05) in the superovulated than the unstimulated heifers. After PG, mean serum progesterone and estradiol concentrations were higher (P ≤ 0.05), LH pulse frequency and amplitude (P ≤ 0.001), and basal serum LH concentration (P ≤ 0.05) were lower in the superovulated than in the unstimulated heifers. After PG injection, the superovulated heifers had reduced FSH pulse amplitude compared with that before the injection (P ≤ 0.05). In the superovulated cows, the suppression of LH and FSH secretion was caused by the negative effects of higher concentrations of estradiol and progesterone in the hypothalamic-hypophysal axis. In the superovulated heifers, 30 h after PG treatment, serum estradiol concentration and LH pulse frequency were positively correlated with the number of CL, total number of embryos, and transferable number of embryos recovered (P ≤ 0.05).

Androgen negative feedback during the early rise in LH secretion in bull calves

A transient elevation in mean circulating concentrations of LH and FSH occurs in the young bull calf prior to 24 weeks of age. The functional significance of this is not clear. To see if changes in the ability of androgens to suppress gonadotrophin secretion were involved in the start of this early rise in LH secretion or the cessation of the early rise in LH and FSH secretion, bull calves were treated with flutamide (androgen receptor blocker; n = 5; 9 mg flutamide/kg body weight in propylene glycol (i.m./s.c.) in three equal portions at 12-h intervals) at 8, 16 and 24 weeks of age and bled every 15 min for 12 h beginning after the third flutamide treatment; control bulls received vehicle at these times. Control bulls (n = 5) were bled every 15 min for 12 h at 4, 8, 12, 16 and 24 weeks of age, and all bulls were bled weekly. Serum samples were assayed for concentrations of LH, FSH and testosterone. Based on weekly and intensive bleedings for control and flutamide-treated bulls, an early rise in LH (8-18 weeks of age) and FSH (4-24 weeks of age) secretion was seen in all bull calves (P < 0.05). At 8 weeks of age flutamide treatment resulted in increased mean serum LH concentrations (P < 0.05); at 16 weeks of age it resulted in increased basal and mean LH concentrations and increased LH pulse frequency (P < 0.05); and at 24 weeks of age in increased mean LH concentrations, LH pulse frequency and amplitude (P < 0.05) in comparison with control bulls.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of NMDA and non-NMDA receptor antagonists on pulsatile luteinizing hormone secretion in the adult male rat.

To determine the physiological role of excitatory amino acids (EAAs) in the pulsatile secretion of LH and FSH in the adult male rat, specific antagonists for N-methyl-D-aspartic acid (NMDA) receptors [2-amino-5-phosphono-pentanoic acid (AP-5, 10 micrograms)] and quisqualate/kainate (non-NMDA) receptors [6,7-dinitroquinoxaline-2,3-dione (DNQX; 30 nM)] were administered through intracerebroventricular injection to orchiectomized adult rats. Blood samples were collected from indwelling jugular catheters at 10-min intervals for plasma LH and FSH determinations. The results revealed that administration of a single central injection of AP-5 significantly suppressed LH and FSH mean levels, trough levels and pulse amplitude but not pulse frequency. The non-NMDA receptor antagonist DNQX had no effect on any parameter of LH or FSH secretion after a single central injection. In a second set of experiments, three central injections of the EAA antagonists at 0, 20 and 40 min were utilized in order to give a more prolonged block of the EAA receptors and the effect on pulsatile LH secretion was determined. Regardless of the three injections, AP-5 still did not significantly alter LH pulse frequency. However, the prolonged treatment with DNQX now significantly suppressed mean and trough LH levels as well as LH pulse amplitude with no effect observed on LH pulse frequency. Taken as a whole, the present studies suggest that EAAs are involved in enhancing gonadotropin pulsatility in the male rat and that the effect is exerted primarily on pulse amplitude rather than pulse frequency.

Effects of a long-acting gonadotrophin-releasing hormone agonist (Leuprolide) on ovarian follicular development in prepubertal heifer calves

We studied the effects of reducing gonadotrophin secretion on ovarian follicular development in young prepubertal heifer calves. Calves received a GnRH agonist (n = 5, 15 mg of Leuprolide acetate, i.m.) or carrier (n = 5) at 8 and 12 w of age. Starting at 8 and 34 w of age, ovarian follicles were monitored daily for 17 d, and at 10, 15, 25 and 35 w of age, blood samples were collected every 15 min for 12 h for measurement of serum concentration of LH and FSH. GnRH agonist treatment did not affect the age and body weight at puberty (P &gt; 0.05). Agonist treatment suppressed follicle numbers and in two heifers follicle emergence (growth above 4–5 mm) was blocked immediately. In three agonist-treated heifers, follicle emergence was blocked after one extended wave of follicular growth. At 34 w of age the pattern of ovarian follicular growth did not differ between groups but oestradiol secretion was lower in agonist-treated heifers. During agonist treatment basal and mean concentrations of FSH, and LH and FSH pulse amplitude were decreased but basal LH concentrations increased (P &lt; 0.05). At 25 and 35 w of age some rebound in gonadotrophin secretion was seen.We concluded that disrupting gonadotrophin secretion in young prepubertal heifer calves by GnRH agonist treatment, suppressed ovarian follicular growth but that a rebound in gonadotrophin secretion prevented long term-effects on sexual development. Key words: Follicle stimulating hormone, gonadotrophin-releasing hormone, heifer calves, luteinising hormone ovarian follicles

A physiological role for N-methyl-D-aspartic acid and non-N-methyl-D- aspartic acid receptors in pulsatile gonadotropin secretion in the adult female rat

The present study was designed to evaluate the physiological role of excitatory amino acids (EAAs) in the pulsatile secretion of LH and FSH. Specific antagonists for N-methyl-D-aspartic acid (NMDA) receptors and kainate/quisqualate (non-NMDA) receptors were used to achieve this aim. Adult female rats (250-280 g), ovariectomized for 2 weeks, were implanted with a cannula in the third ventricle of the brain. One week later, 2-amino-5-phosphono-pentanoic acid (AP-5; 10 micrograms/rat), a specific competitive NMDA receptor antagonist; 6,7-dinitroquinoxaline-2,3-dione (DNQX; 30 nM), a selective antagonist of non-NMDA receptors; or the same volume of saline, was injected via the third ventricle to conscious and unrestrained ovariectomized animals. Blood samples were collected from indwelling jugular catheters 20 min before and after injection and at 10-min intervals for 100 min for plasma LH and FSH determinations. The results revealed that the administration of either AP-5 or DNQX significantly suppressed mean as well as trough LH levels. This suppression was accompanied by a suppression of LH pulse frequency and LH pulse amplitude. AP-5 suppressed LH pulse amplitude, through LH levels, and mean LH levels to a greater degree than DNQX. The analysis of FSH pulses showed that AP-5 inhibited mean and trough FSH levels, and this appeared to be achieved by the suppression of FSH pulse amplitude, but not frequency. DNQX, on the other hand, did not significantly alter FSH pulse frequency, pulse amplitude, or trough or mean FSH levels. Taken as a whole, the present study provides evidence that endogenous EAAs, acting through both NMDA and non-NMDA receptors, play an important physiological role in the generation of pulsatile LH secretion in adult female rats. FSH pulse frequency was not significantly affected by the administration of either EAA receptor antagonist, although AP-5 did suppress FSH pulse amplitude and mean and trough FSH levels.

A physiological role for N-methyl-D-aspartic acid and non-N-methyl-D-aspartic acid receptors in pulsatile gonadotropin secretion in the adult female rat.

The present study was designed to evaluate the physiological role of excitatory amino acids (EAAs) in the pulsatile secretion of LH and FSH. Specific antagonists for N-methyl-D-aspartic acid (NMDA) receptors and kainate/quisqualate (non-NMDA) receptors were used to achieve this aim. Adult female rats (250-280 g), ovariectomized for 2 weeks, were implanted with a cannula in the third ventricle of the brain. One week later, 2-amino-5-phosphono-pentanoic acid (AP-5; 10 micrograms/rat), a specific competitive NMDA receptor antagonist; 6,7-dinitroquinoxaline-2,3-dione (DNQX; 30 nM), a selective antagonist of non-NMDA receptors; or the same volume of saline, was injected via the third ventricle to conscious and unrestrained ovariectomized animals. Blood samples were collected from indwelling jugular catheters 20 min before and after injection and at 10-min intervals for 100 min for plasma LH and FSH determinations. The results revealed that the administration of either AP-5 or DNQX significantly suppressed mean as well as trough LH levels. This suppression was accompanied by a suppression of LH pulse frequency and LH pulse amplitude. AP-5 suppressed LH pulse amplitude, through LH levels, and mean LH levels to a greater degree than DNQX. The analysis of FSH pulses showed that AP-5 inhibited mean and trough FSH levels, and this appeared to be achieved by the suppression of FSH pulse amplitude, but not frequency. DNQX, on the other hand, did not significantly alter FSH pulse frequency, pulse amplitude, or trough or mean FSH levels. Taken as a whole, the present study provides evidence that endogenous EAAs, acting through both NMDA and non-NMDA receptors, play an important physiological role in the generation of pulsatile LH secretion in adult female rats. FSH pulse frequency was not significantly affected by the administration of either EAA receptor antagonist, although AP-5 did suppress FSH pulse amplitude and mean and trough FSH levels.

Serum hormones in response to estradiol and (OR) progesterone in ovariectomized cows after thyroidectomy

To evaluate the effect of gonadal steroid treatment and thyroidectomy on concentrations of gonadotropins and thyroid-stimulating hormone in the bovine, nonlactating Holstein cows were either thyroidectomized and ovariectomized (THYOVEX; n=6) or ovariectomized only (OVEX; n=4), and subsequently treated with no gonadal steroids (control), estradiol-17β (E 2), progesterone (P 4), or P 4+E 2 in a 2 × 4 factorial experiment. Averaged across steroid treatments, baseline concentrations of luteinizing hormone (LH; P < .05) and follicle-stimulating hormone (FSH; P <.10) were higher in THYOVEX cows than in OVEX cows. Pulse frequencies and amplitudes of LH and FSH did not differ between THYOVEX and OVEX cows. Secretion of TSH was pulsatile and all concentrations and pulsatile characteristics of TSH were increased (P < .05) in THYOVEX compared to OVEX cows. Treatment with E 2 and P 4 decreased (P < .05) baseline concentrations and magnitude of LH pulses, whereas P 4+E 2 increased (P < .01) pulse frequency of LH and FSH. Amplitude of LH and FSH pulses were not affected by treatment with either steroid. Treatment with P 4+E 2 decreased (P < .05) baseline concentrations of TSH, whereas pulse frequency, and magnitude and amplitude of TSH pulses were not altered by treatment with steroids. Mean concentrations of LH and FSH were similar during 48 hr after termination of E 2 and P 4+E 2 treatments, but concentrations of TSH were higher (P = .06) after P 4+E 2 than after E 2. Secretion of TSH showed a diurnal variation, with the lowest concentrations in the morning and highest in the afternoon. These results indicate that thyroidectomy influenced secretion of gonadotropins in OVEX cows.

Evidence for a role for the cyclic adenosine 3',5'-monophosphate/protein kinase-A pathway in regulation of the gonadotropin subunit messenger ribonucleic acids.

cAMP regulation of gonadotropin secretion and subunit mRNA levels was studied in pituitary cells perifused with pulses of GnRH. Pituitary cells from 7-week-old male rats castrated at 5 weeks of age were stimulated hourly for 9-24 h with 1-min pulses of GnRH, the adenylate cyclase activator forskolin, the cell-permeable cAMP analog 8-bromo-cAMP (8Br-cAMP), or control medium. Cells were also treated with the nonsteroidal antiinflammatory drug flufenamic acid, which reduces pituitary cAMP levels. During perifusion, the effluent was collected in 10-min fractions for FSH and LH assay. At the completion of perifusion, total RNA was extracted, and gonadotropin subunit mRNA levels were quantitated by Northern analysis. Continuous administration of flufenamic acid gradually reduced the amplitude of GnRH-stimulated FSH and LH pulses to nadir values of 40 +/- 4.7% and 62 +/- 12% of the control value, respectively. Flufenamic acid decreased (P < 0.05) FSH beta and alpha-subunit mRNA levels and blocked the effect of GnRH to lengthen LH beta mRNA. Pulses of forskolin or 8Br-cAMP released LH and FSH, and continuous forskolin or 8Br-cAMP potentiated the gonadotropin stimulatory effect of GnRH. Forskolin or 8Br-cAMP increased (P < 0.05) FSH beta mRNA and alpha-subunit mRNA levels when administered in pulses, but not when administered continuously, and lengthened LH beta mRNA. The Nal-Glu GnRH antagonist blocked the effects of GnRH pulses, but not the effects of 8Br-cAMP or forskolin. In conclusion, lowering intracellular cAMP levels with flufenamic acid attenuated GnRH-stimulated gonadotropin secretion, decreased alpha-subunit and FSH beta mRNA levels, and blocked the effect of GnRH to lengthen LH beta mRNA, whereas 8Br-cAMP or forskolin produced the opposite effect. These data extend previous results which suggested that cAMP modulates gonadotropin secretion and indicate that the cAMP/A-kinase pathway regulates each of the gonadotropin subunit mRNAs.

Evidence for a role for the cyclic adenosine 3',5'- monophosphate/protein kinase-A pathway in regulation of the gonadotropin subunit messenger ribonucleic acids

cAMP regulation of gonadotropin secretion and subunit mRNA levels was studied in pituitary cells perifused with pulses of GnRH. Pituitary cells from 7-week-old male rats castrated at 5 weeks of age were stimulated hourly for 9-24 h with 1-min pulses of GnRH, the adenylate cyclase activator forskolin, the cell-permeable cAMP analog 8-bromo-cAMP (8Br-cAMP), or control medium. Cells were also treated with the nonsteroidal antiinflammatory drug flufenamic acid, which reduces pituitary cAMP levels. During perifusion, the effluent was collected in 10-min fractions for FSH and LH assay. At the completion of perifusion, total RNA was extracted, and gonadotropin subunit mRNA levels were quantitated by Northern analysis. Continuous administration of flufenamic acid gradually reduced the amplitude of GnRH-stimulated FSH and LH pulses to nadir values of 40 +/- 4.7% and 62 +/- 12% of the control value, respectively. Flufenamic acid decreased (P < 0.05) FSH beta and alpha-subunit mRNA levels and blocked the effect of GnRH to lengthen LH beta mRNA. Pulses of forskolin or 8Br-cAMP released LH and FSH, and continuous forskolin or 8Br-cAMP potentiated the gonadotropin stimulatory effect of GnRH. Forskolin or 8Br-cAMP increased (P < 0.05) FSH beta mRNA and alpha-subunit mRNA levels when administered in pulses, but not when administered continuously, and lengthened LH beta mRNA. The Nal-Glu GnRH antagonist blocked the effects of GnRH pulses, but not the effects of 8Br-cAMP or forskolin. In conclusion, lowering intracellular cAMP levels with flufenamic acid attenuated GnRH-stimulated gonadotropin secretion, decreased alpha-subunit and FSH beta mRNA levels, and blocked the effect of GnRH to lengthen LH beta mRNA, whereas 8Br-cAMP or forskolin produced the opposite effect. These data extend previous results which suggested that cAMP modulates gonadotropin secretion and indicate that the cAMP/A-kinase pathway regulates each of the gonadotropin subunit mRNAs.

Opioidergic regulation of gonadotrophin secretion in the early prepubertal bull calf

The control of gonadotrophin secretion during the early developmental period in the bull is poorly understood; opioidergic regulation may be involved. The opioid antagonist naloxone was administered to bull calves (i.v. n = 5; 1 mg kg-1 body weight h-1) for 12 h at 4, 12, 18, 24 and 32 weeks of age. Control animals (n = 5) received sterile saline solution. During the treatment period, 4 ml blood samples were collected every 12 min. The calves were also weighed and blood samples collected every two weeks from 2 to 48 weeks of age. Scrotal circumference was measured from 20 to 48 weeks of age to determine age at puberty. Serum samples were assayed for concentrations of LH, FSH, testosterone and oestradiol. On the basis of blood samples taken every two weeks, serum concentrations of LH increased to a peak at six weeks of age and then decreased; serum concentrations of FSH reached a peak at 20 weeks of age. Serum concentrations of testosterone and oestradiol increased with scrotal circumference from 20 to 48 weeks of age. On the basis of blood samples taken every 12 min for 12 h, we concluded that the early rise in serum LH concentrations was due to an increase in LH pulse frequency. LH pulse amplitude decreased from 4 to 18 weeks of age and FSH pulse amplitude from 4 to 32 weeks of age. Naloxone treatment increased LH pulse frequency at 4 and 24 weeks of age but not at 12, 18 or 32 weeks of age.(ABSTRACT TRUNCATED AT 250 WORDS)