Peak Serum LH Research Articles

Initiation of periovulatory events in primate follicles using recombinant and native human luteinizing hormone to mimic the midcycle gonadotropin surge.

The amplitude and duration of the midcycle LH surge required for periovulatory changes in the primate follicle are incompletely defined. We reported that short (4- to 14-h) LH surges were insufficient to induce periovulatory events after multiple follicular development in macaques. In contrast, an 18- to 24-h LH surge induced oocyte maturation plus granulosa cell luteinization, but did not support corpus luteum function. In this study, the periovulatory changes following LH surges of 48 h elicited using pituitary (pit) or recombinant (r) human (h) LH were compared to those after 24-h LH surge durations or after urinary hCG (u-hCG) treatment. Beginning at menses, rhesus monkeys were treated with human gonadotropins for 9 days to stimulate follicular growth. On day 10, animals (n = 3-5/group) received 1) a single injection of u-hCG [79 +/- 3 micrograms RP-1 equivalents (equiv), im], 2) two injections of pit-hLH (91 +/- 4 micrograms RP-1 equiv, im), 3) one injection of r-hLH (21 +/- 1 micrograms RP-1 equiv, im), or 4) two injections of r-hLH (21 +/- 1 micrograms RP-1 equiv). Oocytes and granulosa cells were obtained via follicle aspiration 27 h after the initial LH or hCG injection. In all groups, serum estradiol rose to similar peak levels by day 10. Circulating LH-like bioactivity was elevated for more than 48 h after u-hCG. Peak serum LH bioactivities were proportional to the administered LH doses, as determined in the in vitro bioassay. Two injections of either r-hLH or pit-hLH elicited surge levels (> 100 ng/mL) of bioactive LH for 36-48 h, whereas one injection sustained surge levels for only 18-24 h. The proportions of oocytes resuming meiosis (68-76%) were similar in all groups. Immunocytochemical staining for progesterone receptor and in vitro progesterone production by granulosa cells in all LH-treated groups were comparable to those of cells form the hCG-treated group. Peak levels of progesterone in the luteal phase were comparable in monkeys treated with two doses of pit-hLH and r-hLH (18.5 +/- 10.4 vs. 8.1 +/- 1.5 ng/mL) and approached that in u-hCG treated monkeys (39.5 +/- 18.0 ng/mL). However, progesterone levels in animals treated once with r-hLH (3.4 +/- 1.5 ng/mL) were less (P < 0.05) than those in u-hCG-treated monkeys.(ABSTRACT TRUNCATED AT 400 WORDS)

Release of glutamate and aspartate from the preoptic area during the progesterone-induced LH surge: in vivo microdialysis studies.

To examine the role of excitatory amino acid neurotransmitters in the regulation of LH and FSH secretion in ovariectomized (ovx) adult rats treated with estradiol and progesterone, we measured the release rates of the excitatory amino acid neurotransmitters, glutamate and aspartate, as well as the neurally inactive amino acid serine in microdialysis perfusate samples of the preoptic area (POA) of the hypothalamus collected at 30-min intervals during the LH surge induced by progesterone. The concentrations of the amino acids were measured by assay using orthophthalaldehyde prederivatization followed by HPLC coupled with fluorometric detection. The release rates of glutamate in the POA increased at 15:30 and 16:00 h in the progesterone-treated estrogen-primed ovx rat as compared to estrogen controls. Release rates of aspartate in the POA were increased at 12:00, 12:30, 15:00 and 16:00 h in the progesterone-treated estrogen-primed ovx rat as compared to estrogen controls. The increase in POA release rates of glutamate and aspartate in the progesterone-treated rats occurred immediately prior to peak serum LH levels induced by progesterone. The specificity of the increase in POA release rates of glutamate and aspartate was evidenced by the finding that the preoptic release of neurally inactive neurotransmitter serine was unchanged by steroid treatment. Estradiol alone had no significant effect on the POA release rates of glutamate, aspartate or serine as compared to ovariectomized controls. In conclusion, the present study demonstrates that the POA release rates of glutamate and aspartate are increased immediately preceding the peak of the progesterone-induced LH surge in the estrogen-primed adult ovx rat.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of an antiprogestin, mifepristone, and an antiestrogen, tamoxifen, on endometrial 17 beta-hydroxysteroid dehydrogenase and progestin and estrogen receptors during the luteal phase of the menstrual cycle: an immunohistochemical study.

The effects of a progesterone antagonist, mifepristone (RU486), and an estrogen antagonist, tamoxifen, given during the early luteal phase on endometrial 17 beta-hydroxysteroid dehydrogenase (17HSD) and estrogen (ER) and progesterone (PR) receptors were studied. Eleven regularly menstruating women were studied during control and treatment cycles. In the treatment cycle on day LH + 2 (2 days after the peak serum LH concentration), 10 subjects received a single dose of 200 mg mifepristone, and 9 received 2 doses of 40 mg tamoxifen on days LH + 2 and LH + 3. In addition, 4 subjects received 400 mg mifepristone in a separate treatment cycle. 17HSD, ER, and PR were measured immunohistochemically in endometrial tissue specimens taken on days LH + 6 to LH + 8. Blood samples were conducted during control and treatment cycles, and serum estradiol, progesterone, and LH concentrations were quantified by RIA. Administration of mifepristone blocked the induction of 17HSD by progesterone and prevented the expression of 17HSD in gland and surface epithelial cells in 8 patients. In 2 patients, staining of 17HSD was seen during both the control and mifepristone treatment cycles. The higher dose of mifepristone additionally given to four subjects did not block the expression of 17HSD in 2 cases where blocking was observed with the lower dose of mifepristone, and in 1 of these patients, very strong staining of 17HSD was observed in basal cells beneath the epithelial cells. ER and PR showed intense staining in the nuclei of both gland and stromal cells in mifepristone treatment cycles, whereas receptor staining was faint or absent in the respective control cycles. Tamoxifen did not have any significant effect on staining of 17HSD or the abundance of receptors. Serum concentrations of estradiol, progesterone, and LH were not significantly affected by the administration of mifepristone or tamoxifen. This study reveals that mifepristone, administered in the early luteal phase, usually blocks the expression of 17HSD and the down-regulation of PR and ER. However, the expression of 17HSD in some patients may reflect the ineffectiveness of the mifepristone treatment used to prevent implantation in certain subjects.

CHANGES IN SERUM AND URINARY LH/FSH RATIO DURING PUBERTY

Serum gonadotropin responses after GnRH stimulation and secretion of LH and FSH in nocturnal urine samples were measured by ultrasensitive time-resolved immnunofluorometric assay, for 95 subjects (62 boys, 33 girls; age 2-14 yrs) with non-endocrine short stature or obesity. The subjects were classified according to sex and pubertal stage. The prepubertal children were divided into two groups, according to chronological age (below or above 10 yrs). The basal and peak serum LH levels after GnRH stimulation and urinary LH showed a gradual increase throughout the pubertal development, while changes in FSH were not as remarkable as for LH. The peak LH/peak FSH ratio after GnRH stimulation and urinary LH/FSH ratio reliably discriminated between prepubertal and early pubertal groups. The reference ranges (mean-SD-mean+SD, after logarithmic transformation) of serum peak LH/peak FSH ratio in prepubertal group and early pubertal group were 0.28-0.55, 1.4-3.4 in boys and 0.09-0.25, 0.74-1.4 in girls, respectively, while urinary LH/FSH ratio in each group ranged 0.03-0.13, 0.37-1.1 in boys and 0.02-0.07, 0.14-0.36 in girls, respectively.

Dynamic changes in hypothalamic angiotensin II levels and release in association with progesterone-induced luteinizing hormone surge.

To test the hypothesis that brain angiotensin II (Ang II) may be involved in the preovulatory release of LH on proestrus, we evaluated the pattern of changes in hypothalamic Ang II levels and release in ovariectomized (ovx) rats treated sequentially with estrogen and progesterone. This is an experimental paradigm that reliably evokes dynamic changes in hypothalamic LHRH levels in association with LH hypersecretion, simulating the LH surge on proestrus. Rats were ovx and after 4 weeks received estradiol benzoate followed by progesterone 2 days later at 1000 h. We observed that in these progesterone-treated rats, serum LH levels were low until 1400 h, but thereafter, the rate of LH secretion increased and remained elevated at 1600 h when the experiment was terminated. In these rats, hypothalamic Ang II levels increased abruptly at 1330 h and returned rapidly to baseline levels before the onset of LH surge. Also, a similar pattern in hypothalamic Ang II levels occurred at 1500 h with the rise and peak serum LH levels in the late afternoon. In the second experiment, Ang II levels in the cerebrospinal fluid (CSF) of rats similarly pretreated with ovarian steroids were evaluated. Again, CSF Ang II levels rose abruptly to a peak at 1330 h and returned to baseline range preceding the expected rise in serum LH. Thereafter, no further change in CSF Ang II levels was detected during the period of LH hypersecretion. In the third experiment, perfusates were collected from a push-pull cannula aimed at the paraventricular nucleus in ovx rats similarly treated with ovarian steroids. A peak of Ang II was observed at 1330 h and a later peak at 1430 h. A comparison with LH profiles indicated that these peaks in Ang II levels were evident before and during the LH surge. Thus, in three separate experiments, the results showed that rapid dynamic changes in hypothalamic Ang II levels and release occur in association with the progesterone-induced LH surge in estrogen-primed ovx rats. These findings support the previous observations that Ang II can stimulate LHRH and LH release. Since similar, temporally correlated changes occur in hypothalamic neuropeptide Y and LHRH, the peptides involved in the induction of LH surge, these results are in agreement with the hypothesis that Ang II-expressing neurons may play an important role in the hypothalamic circuitry responsible for stimulation of LH surge in ovarian steroid-treated ovx rats.

Dynamic changes in hypothalamic angiotensin II levels and release in association with progesterone-induced luteinizing hormone surge

To test the hypothesis that brain angiotensin II (Ang II) may be involved in the preovulatory release of LH on proestrus, we evaluated the pattern of changes in hypothalamic Ang II levels and release in ovariectomized (ovx) rats treated sequentially with estrogen and progesterone. This is an experimental paradigm that reliably evokes dynamic changes in hypothalamic LHRH levels in association with LH hypersecretion, simulating the LH surge on proestrus. Rats were ovx and after 4 weeks received estradiol benzoate followed by progesterone 2 days later at 1000 h. We observed that in these progesterone-treated rats, serum LH levels were low until 1400 h, but thereafter, the rate of LH secretion increased and remained elevated at 1600 h when the experiment was terminated. In these rats, hypothalamic Ang II levels increased abruptly at 1330 h and returned rapidly to baseline levels before the onset of LH surge. Also, a similar pattern in hypothalamic Ang II levels occurred at 1500 h with the rise and peak serum LH levels in the late afternoon. In the second experiment, Ang II levels in the cerebrospinal fluid (CSF) of rats similarly pretreated with ovarian steroids were evaluated. Again, CSF Ang II levels rose abruptly to a peak at 1330 h and returned to baseline range preceding the expected rise in serum LH. Thereafter, no further change in CSF Ang II levels was detected during the period of LH hypersecretion. In the third experiment, perfusates were collected from a push-pull cannula aimed at the paraventricular nucleus in ovx rats similarly treated with ovarian steroids. A peak of Ang II was observed at 1330 h and a later peak at 1430 h. A comparison with LH profiles indicated that these peaks in Ang II levels were evident before and during the LH surge. Thus, in three separate experiments, the results showed that rapid dynamic changes in hypothalamic Ang II levels and release occur in association with the progesterone-induced LH surge in estrogen-primed ovx rats. These findings support the previous observations that Ang II can stimulate LHRH and LH release. Since similar, temporally correlated changes occur in hypothalamic neuropeptide Y and LHRH, the peptides involved in the induction of LH surge, these results are in agreement with the hypothesis that Ang II-expressing neurons may play an important role in the hypothalamic circuitry responsible for stimulation of LH surge in ovarian steroid-treated ovx rats.

Prolactin and luteinizing hormone secretion in the pregnant pig.

Four pregnant, primiparous, crossbred gilts and six gilts from the same population that had been ovariectomized (OVX) for approximately 3 wk were placed in individual pens in an enclosed building. Blood samples were collected every 30 min for 12 h from all gilts via an indwelling jugular vein cannula when the pregnant gilts were at d 30, 50, 70, 90, and 110 of gestation. Serum was quantified for LH and prolactin (PRL) by RIA. The OVX gilts served as controls to ensure that any variations in serum LH and PRL concentrations observed in the pregnant animals were not due to environmental factors unrelated to pregnancy. Within the pregnant gilts, mean serum LH concentrations, mean basal serum LH concentration, and mean serum LH peak height were similar on all days; however, number of LH peaks on d 30, 50, and 70 were greater (P < .05) than on d 90 and 110, and number of LH peaks on d 50 was greater (P < .05) than that on d 70. Within the pregnant gilts, mean serum PRL concentration, mean basal serum PRL concentration, and mean PRL peak height were greater (P < .001) on d 110 than on all other days; however, number of PRL peaks were similar among days. Parameters of LH and PRL secretion in the OVX and pregnant gilts varied independently. Results of this study indicated that 1) LH secretion does not vary appreciably throughout pregnancy and 2) PRL secretion does not vary significantly during the first 90 d of pregnancy, after which it increases markedly on or before 110 d.

Immunogenetic and hormonal study of cryptorchidism.

Ninety-four cryptorchids, 50 monolateral and 44 bilateral, aged from 2-9.4 yr (mean, 5.1 +/- 0.5 yr), were studied for the hormonal and immunogenetic profile. Pituitary-gonadal function was studied by evaluation of basal and peak GnRH-stimulated serum FSH and LH. In 83 cases, the serum testosterone (T) level was measured before and after CG treatment. No significant differences, between patients and age-matched controls, were found in either FSH or LH levels, whether under basal conditions or after GHRH stimulation. The mean basal serum T level was similar in mono and bilateral cryptorchids and in controls but, on the 15th day after treatment, it was significantly lower in the bilateral cryptorchids (P less than 0.05). CG administration led to testicular descent in 42 patients (23 with monolateral and 19 with bilateral cryptorchidism) and failed in 41 (21 with monolateral and 20 with bilateral cryptorchidism), independently of T increase. Immunogenetic investigation demonstrated that HLA-A11 and A23 were significantly overrepresented in the whole group of cryptorchids in comparison with the controls (P = 0.004 and P = 0.0123, respectively). HLA-A11 was more common in the bilateral form (P less than 0.05), whereas HLA-A29 was more frequent in the monolateral one (P less than 0.05). Forty percent of the bilateral cryptorchids with unsuccessful treatment had the HLA-A11 allele (P less than 0.01) and 70% the HLA-DR5.

Preservation of Pulsatile Luteinizing Hormone Release during Postpartum Lactational Amenorrhea*

To evaluate the pulsatile mode of immunoactive LH release during physiological lactational amenorrhea, we withdrew blood samples at 10-min intervals for 24 h from breastfeeding women (n = 9) at both 3 weeks and 3 months postpartum. Nonlactating women (n = 7) were sampled similarly in the early follicular phase of the normal menstrual cycle. Objective LH pulse analysis revealed that the mean frequencies of pulsatile LH release were similar at both times postpartum and in menstruating young women. By 3 months postpartum, mean serum PRL concentrations had declined 50%, and serum LH peak areas doubled. In contrast, LH interpulse interval, peak duration, and maximal, incremental, and fractional LH pulse amplitude did not change significantly. When deconvolution analysis was used to assess pituitary responses to two pulses of exogenous GnRH at 3 months (vs. 3 weeks) postpartum, we found significant increases in maximal LH secretory rates and the total mass of LH secreted. There was no change in the duration or timing of the evoked LH secretory burst and/or the estimated half-life of endogenous LH. In summary, during lactational amenorrhea, pulsatile LH release occurs at a mean frequency no different from that in the normal early follicular phase. As hyperprolactinemia wanes, there is increased pituitary responsiveness to exogenously administered GnRH and a doubling of spontaneous serum LH concentration peak areas. Such amplitude changes are consistent with the hypothesis of increased endogenous GnRH drive (e.g. augmented GnRH secretion per burst and/or increased pituitary responsiveness to available GnRH) during recovery of the postpartum hypothalamopituitary-ovarian axis.

Impact of season on seminal characteristics and endocrine status of adult free-ranging African buffalo (Syncerus caffer)

Pituitary, gonadal and adrenal activity were compared in free-living, adult African buffalo bulls during the breeding and nonbreeding seasons. Frequent blood samples were collected for 2 h from anaesthetized bulls treated intravenously with saline, gonadotrophin-releasing hormone (GnRH, 200 micrograms), human chorionic gonadotrophin (hCG, 10,000 i.u.) or adrenocorticotrophic hormone (ACTH, 1.5 mg). Electroejaculates also were collected from anaesthetized bulls during the breeding and nonbreeding seasons. Pretreatment testosterone concentrations among bulls varied more during the breeding (0.17-23.0 ng/ml) than the nonbreeding (0.15-2.21 ng/ml) season. The variation within the breeding season was attributed to 8 of 25 bulls producing higher (P less than 0.05) serum testosterone (High-T; 16.28 +/- 2.03 ng/ml) and testicular LH receptor (1.53 +/- 0.22 fmol/mg testis) concentrations compared with their seasonal counterparts (Low-T; 0.95 +/- 0.26 ng/ml; 0.38 +/- 0.04 fmol/mg) or with all bulls during the nonbreeding season (0.90 +/- 0.27 ng/ml; 0.31 +/- 0.04 fmol/mg). The magnitude of GnRH- and hCG-induced increases in serum testosterone was similar (P greater than 0.05) between Low-T bulls and bulls during the nonbreeding season. In the High-T animals treated with GnRH or hCG, serum testosterone did not increase, suggesting that secretion was already maximal. Peak serum LH concentrations after GnRH were greater (P less than 0.05) in bulls during the nonbreeding than the breeding season; FSH responses were similar (P greater than 0.05). ACTH treatment did not increase serum cortisol concentrations above the 2-fold increase measured in bulls treated with saline, hCG and GnRH (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Possibilities for using the LH color test in determining ovulation time

The LH color test was used to monitor 40 cycles of 32 patients. The urine test, which becomes positive at a LH-concentration of at least 50 I. U./ml, indicated the LH-peak in 34 out of 35 cycles with ascertained ovulation. In 24 cycles, the urine LH-peak preceded the serum LH-peak by one day. The urine LH-peak was found on cycle day 13.6 on average. The serum LH-peak on day 14.2 on average. The sensitivity of the LH color test was 97.2%, its specificity 100%.

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.

Vaginal progesterone administration before ovulation induction with exogenous gonadotropins in polycystic ovarian syndrome.

We studied the value of vaginal progesterone (P4) in suppressing serum LH concentrations and restoring normal luteal phase serum LH concentrations before administration of exogenous gonadotropins in anovulatory women with the polycystic ovarian syndrome (PCOS). P4 (50 mg every 12 h) was administered by vaginal suppository to 9 women (18 cycles) for 14 days before ovulation induction with human menopausal gonadotropin (hMG) and hCG. Serum LH, FSH, estradiol, P4, and PRL levels were measured daily. A biphasic effect on LH secretion occurred during P4 administration. Peak serum LH levels occurred on day 5 (125% of basal levels; P less than 0.05) of vaginal P4 suppository use, followed by a progressive fall (P less than 0.05) to 79% of basal levels, but serum LH levels were still higher than those in normal women despite achieving physiological luteal phase P4 concentrations. Ovulation occurred in 56% of cycles after P4 and hMG/hCG treatment and in 65% of control cycles after hMG/hCG alone. In 7 women, serum LH was measured at 10-min intervals for 6 h before and after vaginal P4 administration for 10 days. LH pulse frequency decreased from 7.4 +/- 1.1 to 4.4 +/- 1.2 pulses/6 h (P less than 0.01), and LH pulse amplitude increased from 3.8 +/- 1.8 to 6.1 +/- 2.9 IU/L (P less than 0.01) after P4 administration. We conclude that vaginal P4 (50 mg every 12 h) 1) produces serum P4 concentrations within the normal range for the luteal phase of the menstrual cycle; 2) elevates serum LH, but not FSH, within 5 days; 3) decreases LH pulse frequency and increases LH pulse amplitude after 10 days, but does not normalize serum LH values; and 5) fails to improve the results of subsequent ovulation induction with exogenous gonadotropins in patients with PCOS.

Hormonal evaluation of boys born with undescended testes during their first year of life.

We studied pituitary-gonadal function during the first year of life in 48 boys born with 56 undescended testes in order to test the hypotheses that functional insufficiency of the hypothalamo-pituitary-gonadal axis and disorders of testosterone (T) biosynthesis occur in such boys. Cryptorchidism persisted for longer than 1 yr in 29 boys (30 testes; group I), whereas spontaneous descent occurred in 19 boys (20 testes; group II), in 6 after the sixth month. A control group (group III) included 160 boys. Basal and peak LHRH-stimulated serum LH and FSH and basal serum T values were determined at 3, 6, and 12 months. Serum T, dihydrotestosterone (DHT), progesterone (P), 17-hydroxypregnenolone, 17-hydroxyprogesterone, dehydroepiandrosterone sulfate, and androstenedione before and after hCG administration were determined at age 1 yr. Comparing the 3 groups, cross-sectional evaluation revealed no significant differences in basal or peak LHRH-stimulated serum LH and FSH levels, except that basal serum LH levels were slightly higher in group II than in group III. Comparing groups I and II, longitudinal evaluation revealed similar basal and peak LHRH-stimulated serum LH and FSH values, with comparable changes with time. Basal serum T, DHT, and T precursor levels were similar in all three groups, with similar rises of T and DHT and variable minimal increases in androstenedione and dehydroepiandrosterone sulfate after hCG stimulation. We conclude that during the first year of life, boys with cryptorchidism have no functional insufficiency of the hypothalamo-pituitary-gonadal axis or disorders in T biosynthesis.

Control of gonadotropin secretion in the ovine fetus: the effects of a specific gonadotropin-releasing hormone antagonist on pulsatile luteinizing hormone secretion.

To demonstrate the dependence of fetal pituitary LH secretion endogenous GnRH, we studied the effects of bolus iv administration of a specific GnRH antagonist analog [GnRH-Ant; (N-acetyl-D-p-chloro-Phe1,2,D-Trp3,D-Arg6,D-Ala10)GnRH] on pulsatile LH release in 10 chronically cannulated ovine fetuses of 104-129 days gestation (term, 147 days). Vehicle alone was given to 13 control fetuses of 107-125 days gestation. Blood samples for LH determination by RIA (NIH LH S16 standard) were taken after injection of either GnRH-Ant (175-300 micrograms dissolved in 1 ml 5% dextrose in water) or vehicle alone for 1.75-5 h. The efficacy of GnRH receptor blockade was then assessed by a bolus iv challenge with 50 micrograms synthetic GnRH. The mean (+/- SEM) observation period per animal was similar for the two groups (3.8 +/- 0.2 h for GnRH-Ant; 3.6 +/- 0.2 h for controls). The frequency of spontaneous pulsatile LH secretion was significantly decreased in the fetuses given GhRH-Ant (2 pulses over 38 h total observation vs. 13 pulses over 47.3 h in control fetuses; P = 0.006). The average interpulse interval was 19.0 h in the GnRH-Ant group compared to 3.6 h in controls. Although the mean pulse amplitude was lower in the GnRH-Ant group (2.8 +/- 1.2 vs. 7.6 +/- 1.1 ng/ml for controls), this difference was not statistically significant (P = 0.065, by one-tailed t test). The mean peak serum LH concentration in response to the GnRH challenge was significantly blunted in the GnRH-Ant group (4.6 +/- 0.8 vs. 20.6 +/- 1.8 ng/ml for controls; P less than 0.001). These results indicate that GnRH-Ant administration causes a virtual cessation of pulsatile LH discharge. As this GnRH-Ant blocks GnRH action at the receptor level, these data demonstrate that pulsatile LH secretion in the ovine fetus is dependent on endogenous GnRH release as early as 104 days gestation.

Effects of long- and short-term gonadectomy on the hypothalamo-hypophysial (LH-releasing hormone-LH) system in oestrogen-treated male and female rats.

Considerable differences have previously been found in the hypothalamo-hypophysial responsiveness to oestrogen, depending upon the time between gonad removal and exposure to oestrogen. In the present study a detailed analysis was made of some of the differences which may exist in pituitary LH-releasing hormone (LHRH) receptors and the amount of LH released in response to electrochemical depolarization of the medial preoptic area after 2 or 7 days of oestradiol treatment of long- and short-term gonadectomized male and female rats. The pituitary glands of long-term gonadectomized males and females secreted more LH in response to two pulse injections of LHRH than did short-term gonadectomized rats. The amount of LH released on day 2, however, was equivalent to that secreted after 7 days of oestradiol treatment. Moreover, long-term gonadectomized males and females had equivalent LHRH receptor concentrations, which were greater than those of short-term gonadectomized animals. Peak serum LH concentrations observed after preoptic stimulation were equivalent in short- and long-term castrated rats after 2 days of oestrogen exposure. Serum LH concentrations following preoptic stimulation in short-term gonadectomized males and females were significantly greater on day 7 than on day 2 of oestradiol treatment, whereas in long-term gonadectomized animals the stimulated release of LH was equivalent both in magnitude and time of peak release on both days.(ABSTRACT TRUNCATED AT 250 WORDS)

Patterns of changes in glycoproteins, polypeptides, and steroids in the peritoneal fluid of women during the periovulatory phase of the menstrual cycle.

During laparoscopy peritoneal fluid samples were collected for FSH, LH, PRL, 17 beta-estradiol, progesterone, and total protein determinations in 100 women with a normal menstrual cycle. The samples were collected between cycle day -6 and cycle day +9, with the serum LH peak as a point of reference (day 0). The period investigated was divided into seven phases. FSH and LH concentrations in the peritoneal fluid varied in a cycle-dependent pattern that reflected the pattern in serum. In every phase of the cycle, however, peritoneal fluid FSH and LH concentrations were higher than or equal to the serum levels. This finding contrasts with the physiological behavior of other proteins in the peritoneal fluid. Peritoneal fluid 17 beta-estradiol and progesterone levels also varied in a cyclic pattern, with an increase in concentration immediately after ovulation and a decrease after the midluteal phase. With the exception of 17 beta-estradiol levels during the preovulatory phase of the cycle, peritoneal fluid levels of 17 beta-estradiol and progesterone were always equal to or higher than serum levels. The increase in 17 beta-estradiol concentration in the postovulatory phase was more gradual than that in the progesterone concentration. The elevated peritoneal fluid levels of gonadotropins in the preovulatory phase of the menstrual cycle were the most striking finding of the present study. This together with the finding of high peritoneal fluid to serum ratios of steroid hormones after ovulation shed new light upon the surroundings in which follicular development, ovulation, and fertilization take place.

Homologous ligand regulation of gonadotrophin-releasing hormone receptors in vivo: relationship to gonadotrophin secretion and gonadal steroids.

A single injection of gonadotrophin-releasing hormone (GnRH) (60 ng s.c., 42.9 nmol) induced biphasic GnRH receptor regulation in normal intact adult female mice. A transient 22% receptor decrease occurred 30-60 min after injection of GnRH when peak serum decapeptide concentrations were reached (137 +/- 41 (S.E.M.) ng/l). This GnRH receptor decrease occurred shortly after the peak serum LH values at 15-30 min. The subsequent rapid (within 1 h) return of GnRH receptor levels to normal suggested transient receptor occupancy by GnRH rather than true receptor loss. At 8 h after injection of GnRH a significant 35% increase in GnRH receptors was consistently observed, when serum GnRH levels were undetectable and serum LH had returned to basal levels. This receptor increase was not due to increased receptor affinity, and was prevented by a non-specific protein synthesis inhibitor. Ovariectomy, which caused a 50% fall in GnRH receptors (59.4 +/- 4.9 fmol/pituitary gland in intact controls; 26.9 +/- 2.6 in ovariectomized mice) abolished the induction by GnRH of its own receptors, although the initial transient decrease occurred over the period of the acute serum LH and FSH rise. Despite a 50% reduction in GnRH receptors in ovariectomized mice, increased serum gonadotrophin levels and responsiveness to GnRH were maintained, indicating dissociation between receptor changes and gonadotrophin levels. No GnRH receptor up-regulation was observed 8 h after a single GnRH injection (60 ng s.c.) in either intact or orchidectomized normal male mice. However, the same treatment doubled GnRH receptors in GnRH-deficient (hpg) female mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Modification of the oestrous cycle hormonal profile by dietary restriction

In fully fed female CFY Sprague-Dawley rats there was a significant increase in oestrous cycle length with increasing age and a decrease in the percentage of rats with cycles of regular duration. Modification of the rate of reproductive decline could be achieved by restriction of food intake from weaning. Such animals showed retention of regular cycles to a greater age and there was no age-associated change in the length of the oestrous cycle. In dietary restricted females the serum LH peak occurred earlier in the cycle and serum oestradiol-17β rose later than in fully fed animals. Both peaks were of reduced amplitude. Serum progesterone values were reduced overall by dietary restriction. Underfeeding resulted in both an increase in serum FSH values and a significant modification of the serum FSH profile.

Changes in pituitary responsiveness to LH-releasing hormone after acute buserelin treatment: a time-course and dose-response study.

The acute in-vivo effects of a potent LH-releasing hormone (LHRH) agonist, buserelin, on LH secretion and pituitary responsiveness to LHRH have been investigated in oestrous rats. Doses of 50, 100 and 250 ng buserelin stimulated LH release in a dose-dependent manner, the peak serum LH concentrations being measured 1 h after the treatment. Thereafter LH levels fell rapidly between 1 and 6 h and by 18 h serum LH concentrations were similar in all groups of animals. Pituitary responsiveness to a challenge with 100 ng LHRH was potentiated by 50 or 100 ng buserelin injected 1 or 2 h before the LHRH challenge. In contrast, 250 ng buserelin completely abolished the LH response to LHRH when tested 1, 2 and 4 h after treatment, but by 6 h a small but attenuated response was observed. Four hours after treatment there was no significant difference in the responses when compared with the saline-treated controls.