Differential gonadotropin-releasing hormone stimulation of rat luteinizing hormone subunit gene transcription by calcium influx and mitogen-activated protein kinase-signaling pathways

Gonadotropin secretion and gene expression are differentially regulated by hypothalamic GnRH pulses by unknown mechanisms. GnRH stimulates calcium influx through L-type voltage-gated channels and activates phospholipase C, leading to increased protein kinase C (PKC) and mitogen-activated protein kinase activity. We found differential contributions of these pathways to GnRH-stimulated rat LH subunit transcription in pituitary gonadotropes and cell lines. Endogenous transcription of the alpha- and LHbeta-subunits in rat pituitary cells was stimulated by GnRH. Independent PKC activation by phorbol myristate acid stimulated only the alpha-subunit gene. In contrast, an L-channel antagonist (nimodipine) inhibited only LHbeta stimulation by GnRH, and an L-channel agonist (BayK 8644) stimulated only basal LHbeta transcription. GnRH induction of a rat alpha-subunit promoter construct in alphaT3 cells was unaffected by nimodipine or elimination of external calcium, while both treatments eliminated the LHbeta response. Application of a mitogen-activated kinase kinase (MEK) inhibitor (PD098059) decreased basal and GnRH-stimulated alpha-subunit promoter activity and had no effect on LHbeta promoter activity. In pituitary cells from mice bearing an LHbeta promoter-luciferase reporter transgene, GnRH stimulation was inhibited by nimodipine but not by PD098059. Thus, GnRH induction and basal control of the alpha-subunit gene seem to occur through the PKC/mitogen-activated protein kinase pathway, while induction of the LHbeta gene is dependent on calcium influx. Differential signaling from the same receptor may be a mechanism for preferential regulation of transcription.

Ethanol blocks the central action of IGF-1 to induce luteinizing hormone secretion in the prepubertal female rat

Insulin-like growth factor-1 (IGF-1) is emerging as a signal of peripheral origin capable of acting centrally to induce luteinizing hormone (LH) secretion and accelerate the initiation of female puberty. Since we have shown previously that ethanol (ETOH) can suppress prepubertal LH release and delay female puberty, we hypothesized that these detrimental effects might be due, at least in part, to the drugs ability to alter the central actions of IGF-1. Thus, we have investigated the effects of ETOH on IGF-1 induced LH release in vivo, and on IGF-1 induced prostaglandin-E2 (PGE2) and LH-releasing hormone (LHRH) release in vitro from rats during the juvenile phase of development as well as from rats during the early stage of first proestrus. For the in vivo experiment three initial jugular blood samples were taken at 10-min. intervals from all rats, then the animals received either a 3g/Kg dose of ETOH or an equal volume of saline by gastric gavage. The rats were subsequently left undisturbed for 90 min. to allow time for ETOH absorption, then a single blood sample was drawn from each rat. Finally, IGF-1 (200 ng/3 microl) was microinjected into the third ventricle of all animals and five more blood samples were withdrawn at 10 min. intervals. We demonstrated that IGF-1 induced the release of LH (p<0.01) in the saline controls from rats in both phases of pubertal development. Conversely, this effect of IGF-1 was blocked by ETOH in both developmental groups. For the in vitro experiment, median eminences (MEs) were dissected, then incubated in the presence or absence of ETOH (50 mM). The amount of PGE2 and LHRH released was measured from the same samples following the addition of IGF-1 (100 ng/ml). As above, similar responses were observed from rats in both developmental phases. IGF-1 stimulated the release of PGE2 (p<0.001) and LHRH (p<0.01) from the incubated nerve terminals in the absence of ETOH; however, these effects were blocked by the presence of ETOH. Thus, these combined in vivo and in vitro results suggest that ETOH can acutely block IGF-1 induced LH release during the juvenile-peripubertal transition period, and that this is a centrally mediated action which is due to the diminished formation of PGE2 resulting in decreased LHRH release.

Dimeric inhibin serum values as markers of ovarian activity in pill-free intervals

Levels of inhibin A and B as well as other hormones in serum samples obtained during the pill-free interval in women taking combined oral contraceptives (OC) were measured to asses the extent of ovarian activity during that period. Type of pill and day of pill-free interval were recorded during routine gynecologic check-ups, if patients were in the pill-free period and had taken their pills regularly in the previous cycle. In addition to inhibin A and B, serum levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E2), and progesterone were also quantified. Inhibin B levels rise significantly in parallel with rising levels of FSH, LH, and E2. Progesterone levels were completely suppressed and inhibin A levels rose slightly but insignificantly. Inhibins are sensitive biochemical markers of ovarian activity in pill-free intervals.

A regimen of oral contraceptives restricted to the periovulatory period may permit folliculogenesis but inhibit ovulation

Increased safety of oral contraceptives (OC) has resulted from a reduction in the estrogen and progestin content per tablet. A reduction in the number of hormonally active pills and their placement at critical points within the cycle may provide a novel regimen for further reducing the hormonal content of OC per cycle and their attendant side effects without compromising efficacy. The objective of this study was to determine the effectiveness of two OC regimens that incorporate a delayed start and limited midcycle use of the combination of ethinyl estradiol and norethindrone, and limited use of norethindrone only during the second half of the cycle. Main outcome measures were defined as ovulation, serum concentrations of estradiol (E2), luteinizing hormone (LH), follicle stimulating hormone (FSH), progesterone (P), follicular diameters, and endometrial thickness. Volunteers were issued blister packs containing 28 pills and randomized to one of two groups. Group 1 used a combination of 50 micrograms ethinyl estradiol and 1 mg norethindrone per tablet day 6-10, and 0.70 mg norethindrone only day 11-19. Placebo tablets were used on days 1-5 and day 20-28. Group 2 used a combination of 50 micrograms ethinyl estradiol and 1 mg norethindrone per tablet on day 8-12, and 0.70 mg norethindrone only on day 13-21. Placebo tablets were used on day 1-7 and day 22-28. A total of 20 cycles were studied using 10 volunteers. To assess any possible carryover effect, two successive cycles were studied for each subject. Serum sampling for E2, FSH, LH, and P, and transvaginal ultrasound imaging to assess endometrial thickness and follicle diameter were carried out at 4 day intervals throughout the cycle. One ovulation occurred in 10 cycles in group 1. Five ovulations occurred in 10 cycles in group 2. All ovulations, regardless of group, occurred in the second cycle. Peak E2 concentrations were not significantly different between groups (152.04 +/- 107.1 pg/mL vs 162.1 +/- 56.1 pg/mL [mean +/- SD] for groups 1 and 2, respectively] but occurred earlier in the cycle in group 1. No differences were noted between the groups in serum concentrations of FSH or LH for any given cycle day. Maximum follicle diameters were not different between groups 1 and 2, regardless of ovulatory status (20.5 +/- 8.1 mm2 vs 20.6 +/- 14.2 mm2, respectively). Ultrasound imaging assessment of midcycle follicle growth revealed diameters ranging from 18.5 mm2 to 34.0 mm2 with gradual resolution through the second half of the cycle in anovulatory cycles, and 16.0 mm2 to 23.5 mm2 with abrupt disappearance in ovulatory cycles. Endometrial thickness did not exceed 10 mm for any anovulatory cycle regardless of group, but ranged from 6 to 9 and 6 to 11 during the luteal phase of ovulatory cycles of groups 1 and 2, respectively. Peak serum P concentrations at midluteal phase in ovulatory cycles ranged from 9.2 ng/ml to 18.2 ng/ml. Data from this preliminary study suggest that ovulation may be prevented with a combination of ethinyl estradiol and norethindrone started as late as cycle day 6 and limited to 5 days' duration using norethindrone only for 9 days during the second half of the cycle. Such a restricted regimen may offer both an effective method of contraception and a means of further reducing both estrogen and progestin content per cycle and the possible short and long term adverse side effects of these hormones.

GnRH antagonist inhibition of luteinizing hormone secretion and ovulation in the pig

A GnRH antagonist, Ac-D-p-Cl-Phe1,2, D-Trp3, D-Arg6, D-Ala10 GnRHb (Organon), was utilized to determine the effective dosage and duration to inhibit LH secretion in the pig. In a preliminary trial, barrows received either 10, 50, or 250 micrograms/kg BW of the GnRH antagonist. Secretion of LH was inhibited within 30 min for a duration of 12 h with the 100 micrograms/kg dose but persisted for greater than 48 h with the 250 micrograms/kg treatment. A second study determined effectiveness of the antagonist for inhibiting ovulation in cyclic gilts. At first detection of standing estrus, cyclic gilts were treated with either saline (control), 100, or 200 micrograms/kg BW of the GnRH antagonist (GnRH1). A second group of GnRH antagonist gilts received 200 micrograms/kg BW of the GnRH antagonist approximately 8 h prior to standing estrus (GnRH2). The GnRH1-treatment failed to inhibit or delay ovulation. Ovulation was inhibited and estrous cycles lengthened in GnRH2-treated gilts. These preliminary results suggest that ovulation in the gilt can be inhibited if the GnRH antagonist is administered prior to the LH surge.

Effect of prostaglandin F2 alpha-and gonadotropin releasing hormone-induced luteinizing hormone releases on ovulation and corpus luteum function of beef cows

Luteinizing hormone (LH) concentrations were measured in suckled beef cows treated during the postpartum period with prostaglandin F2 alpha (5 mg Alfaprostol; PGF2 alpha) and then gonadotropin releasing hormone (100 micrograms Cystorelin 30 h after PGF2 alpha; GnRH). The objective was to determine if PGF2 alpha would cause a release of LH in the absence of progesterone and affect the GnRH-induced LH release and ovulation (Experiment 1). LH concentrations increased (P < 0.05) after PGF2 alpha treatment in both anestrous and cyclic cows but to a greater extent (P < 0.05) in anestrous cows. The GnRH-induced LH release and ovulation response in previously anestrous cows were greater (P < 0.05) when PGF2 alpha was administered 30 h earlier. In Experiment 2, 49 beef cows received PGF2 alpha (5 mg Alfaprostol) and GnRH (100 micrograms Cystorelin) 30 h later to determine if the profile of the preovulatory LH surge was associated with the occurrence of subnormal luteal phases in postpartum beef cows suckling calves. Cows that had normal luteal phases had a greater (P < 0.05) mean area under the GnRH-induced LH response curve and a greater (P < 0.05) mean GnRH-induced LH peak amplitude than cows that had subnormal luteal phases. In summary, results suggest that PGF2 alpha may exert a fertility effect by causing a LH release independent of progesterone withdrawal; administration of PGF2 alpha 30 h before GnRH elevated the GnRH-induced LH release and ovulation response. In addition, cows with subnormal luteal phases had GnRH-induced LH surges of less area and peak amplitude than cows with normal luteal phases.

Success of glucocorticoid replacement therapy on fertility in two adult males with 21-CAH homozygote classic form

A normal gonadal maturation with normal fertility are some of the major goals of long-term replacement therapy in adult males with Congenital Adrenal Hyperplasia (CAH). We describe here two young men, G.O. (case A, 23 years old) and S.S.(case B, 24 years old), both with a well defined diagnosis of CAH due to 21-hydroxylase deficiency classic homozygote form (21-CAH). In case A the diagnosis of the 21-CAH classic virilizing form was made at 3 years of age. The patient has undergone glucocorticoid therapy and is now 170 cm tall; all his hormonal findings are within the normal range. The semen analysis has shown a good fertility potential, with a slight modification when the patient decided to discontinue the therapy. In case B the diagnosis of the 21-CAH salt wasting form was performed at 9 days of age. The patient was initially treated with i.v. normal saline solution and a daily i.m. injection of hydrocortisone and, subsequently, with mineral and glucocorticoid replacement therapy po. A satisfactory adult stature (165 cm) was attained. The patient is still on therapy, with a good hormonal profile. The semen analysis has shown an apparently normal fertility. In conclusion, our experience in adult males with 21-CAH, who have been administered prompt and adequate replacement therapy, shows that these patients can attain normal quality of life, satisfactory growth and development, normal sexual maturation and activity, and adequate sperm fertilizing ability, thereby supporting the usefulness of continuing this therapy during adult age.

Gonadotropin-releasing hormone analogue plus hormone replacement therapy for the treatment of endometriosis: a randomized controlled trial

OBJECTIVE

The aim of this study was to determine whether or not continuous combined HRT used with GnRH-a for the treatment of endometriosis can prevent hypoestrogenic side effects associated with GnRH-a.

METHODS

Forty premenopausal women with laparoscopically proven endometriosis entered the study. The patients were randomized into two groups. Group I (n = 19) received 3.75 mg i.m. leuprolide acetate (LA) every 4 weeks for 24 weeks. Group II (n = 21) received 3.7 mg LA combined with 1.25 mg oral conjugated equine estrogen (CEE) and 5 mg oral medroxyprogesterone acetate (MA).

RESULTS

Total revised AFS score as well as total pelvic pain scores decreased significantly (P < .001) in both groups. However, a statistically significant difference of hot flushes and sweating was reported by women receiving LA + HRT as compared to those treated with LA alone (P < .001). Furthermore, the bone loss at the lumbar spine was 4.2% in group I compared to 0.9% in group II at the end of the study.

CONCLUSIONS

This study suggests that 1.25 mg CEE + 5 mg MA is effective in preventing hypoestrogenic side effects caused by GnRH-a, while the treatment of endometriosis is not impaired.

Gonadotropic control of secretion of dimeric inhibins and activin A by human granulosa-luteal cells in vitro

PURPOSE

It is well established that human granulosa cells and luteal cells express inhibin/activin subunit protein and secrete immunoreactive inhibin. The gonadotropic control of secretion of different molecular forms of inhibin and activin A by granulosa-luteal cells (G-LCs) was investigated using recently developed specific enzyme immunoassays (EIAs).

METHODS

Granulosa-luteal cells obtained at IVF egg pickup were cultured in a serum-free medium at 37 degrees C in a water-saturated incubator with 5% CO2 for up to 5 days. Experiments with varying concentrations of human FSH, hLH, and hCG were carried out.

RESULTS

FSH raised the secretion of inhibin A and pro-alpha C-containing inhibins after 24 and 48 hr in culture. Inhibin B was raised after 24 hr and activin A was raised after 48 hr of FSH treatment. LH treatment for 24 hr stimulated inhibin A, inhibin B, pro-alpha C, and activin A. hCG stimulated G-LC secretion of inhibin A after 48 hr and pro-alpha C after 24 hr. Paradoxically, inhibin B secretion was inhibited by 1 and 10 ng/ml hCG after 48 hr. Activin A was stimulated by hCG after 24 and 48 hr of incubation. G-LC secretion of estradiol and progesterone was also stimulated significantly by LH and hCG.

CONCLUSIONS

Secretion of dimeric inhibins and activin A is controlled differentially by gonadotropins.

Differential effect of baclofen on hypothalamic GnRH and pituitary LH beta gene expression in steroid-treated rats

gamma-Aminobutyric acid (GABA) is known to be a major inhibitory neurotransmitter in the brain. The present study was performed to elucidate the possibility of differential roles of baclofen, a GABAB receptor agonist, in gonadotropin releasing hormone (GnRH) and luteinizing hormone beta (LH beta) subunit gene expression. To examine the effect of baclofen on GnRH gene expression in the hypothalamus, it was subcutaneously administered to ovariectomized (OVX) and 17 beta-estradiol (E) and progesterone (P)-treated rats. Baclofen (2 mg) enhanced the GnRH mRNA level and this stimulatory action of baclofen was also confirmed by intracerebroventricular injection of baclofen (2 micrograms). To examine the effect of GABA on LH beta gene expression in the pituitary, the OVX + E-treated model was used rather than the OVX + E + P-treated model because the stimulatory action of baclofen overlapped with that of P. Baclofen (2 mg) was administered subcutaneously to OVX + E-treated rats 48 h after E implants and animals were sacrificed 6 h after administration of baclofen. Baclofen further decreased the LH beta mRNA level which had already been decreased by E, but had no effect on the prolactin mRNA level. The inhibitory effect of baclofen on the LH beta mRNA level lasted at least for 6 h following treatment. The release of LH was decreased by baclofen in the presence of E. The action site of GABA in LH beta subunit gene expression seems to be different from that of P, because the restoration of LH beta mRNA level with RU486 was not suppressed by baclofen. This study suggests that activation of GABAB receptor with baclofen may play differential roles in regulating hypothalamic GnRH and pituitary LH beta gene expression depending on steroid milieu.

Fertility impairment after mifepristone treatment to rats at proestrus. Actions on the hypothalamic-hypophyseal-ovarian axis

Accumulated evidence indicates that the antigestagen mifepristone affects the reproductive axis acting on hypothalamic, pituitary, ovarian, and uterine tissues. The purpose of this study was to further investigate which reproductive functions are impaired by the antagonist, critically compromising the reproductive process, leading to unsuccessful pregnancy. Circulating pituitary and ovarian hormones, sexual receptivity, ovulation, and implantation rates were studied in cycling rats receiving a single dose of mifepristone (1 or 10 mg/kg subcutaneously) at 12:00 proestrus, before luteinizing hormone (LH) stimulation of the ovulatory process. Mifepristone-treated rats had decreased preovulatory surges of LH and prolactin (PRL), and hypersecretion of LH, PRL, and progesterone at estrus. The sexual receptivity was dramatically affected by the antagonist as indicated by the profound decrease in the lordosis response evaluated on the night of proestrus. The number of ovulating animals and the number of oocytes recovered from the oviduct on the morning of estrus were not affected by mifepristone. The low number of rats that succeeded in mating with potent males became pregnant. However, they delivered an average of only two pups at parturition, indicating a failure in the implantation of the fertilized ova, as ovulation was not affected by the antagonist at the dose used. We conclude that a dramatic inhibition of the sexual receptivity and unsuccessful implantation, preceded by a reduction on LH and PRL secretion, are the major components leading to fertility impairment after a single dose of mifepristone administered before the preovulatory surge of LH.

Evidence for the presence of immunoreactive inhibin in extragonadal tissues of ovariectomized ewes

Six ewes were ovariectomized to determine the immediate and long-term effects of removal of ovaries on the immunoreactive concentrations of FSH, LH and inhibin. Three months after ovariectomy, ewes were slaughtered and tissue samples of brain, pituitary, spleen, liver, perirenal fat, lung, kidney, adrenals and uterus were collected to determine the immunoreactive inhibin content. Both gonadotrophins, FSH and LH, increased significantly after ovariectomy. The increase of FSH, however, was more pronounced and remarkably faster than the changes of LH after ovariectomy. Immunoreactive concentrations of inhibin decreased sharply as early as 15 min after ovariectomy and subsequently decreased more gradually until 2 weeks after surgery. From this moment on, the level stabilized at 56% of the initial value. In control ewes, a considerable amount of immunoreactive inhibin is found in tissue samples of ovary, lung, kidney, pituitary and spleen. After ovariectomy, the level of immunoreactive inhibin decreased in spleen and lung samples while an important increase of immunoreactive inhibin is found in adrenals and pituitary. These results demonstrate a differential regulation of LH and FSH after ovariectomy and support an involvement of inhibin only in the immediate changes of FSH after ovariectomy in sheep. They further suggest that the adrenals and the pituitary may be extragonadal sources of inhibin. To explore the eventual contribution of the adrenals to circulating inhibin, dexamethasone (1.4 mg/ewe) and ACTH (200 IU/ewe) were in a following experiment injected intravenously in control and ovariectomized ewes. The lack of any effect of dexamethasone or ACTH on the plasma concentration of immunoreactive inhibin indicate that adrenal inhibin probably does not contribute to circulating inhibin.

Enhancement by prolactin of the GnRH-induced release of LH from dispersed anterior pituitary cells of the bullfrog (Rana catesbeiana)

The response of enzymatically dispersed anterior pituitary cells of the bullfrog (Rana catesbeiana) to gonadotropin-releasing hormone (GnRH) was studied by monitoring the release of luteinizing hormone (LH) into the culture medium. The cells responded to GnRH by releasing LH according to the incubation time and to the GnRH concentration. The responsiveness to GnRH became less conspicuous as the cell density was reduced. Addition of prolactin (PRL) to the medium enhanced the responsiveness to the secretagogue, and addition of antiserum against PRL lowered the responsiveness to a certain extent. Immunohistochemical studies of sectioned pituitaries revealed that PRL cells most frequently located in contact with LH cells. The possibility that PRL acts directly on gonadotrophs to enhance their responsiveness to GnRH was suggested.

Inhibitory effect of leukotrienes on luteinizing hormone release

The aim of this work was to study the effect of high concentrations of leukotrienes on luteinizing hormone (LH) secretion in rat anterior pituitary cells. We also investigated the effect of leukotrienes in parallel with gonadotropin-releasing hormone (GnRH) action. Experiments were on cells gained from trypsinized pituitaries of female rats. Tests were performed by superfusion of the cells attached to cytodex-1 carrier beads. The LH content in samples of perfusate was estimated by radioimmunoassay. This work reports 48% inhibition of basic LH release by action of leukotriene C4 in superfused cells when applied continuously at a concentration of 100 nmol/l. Moreover, we have shown that leukotrienes suppressed GnRH-induced LH secretion in rat pituitary cells when applied in parallel to GnRH (1 nmol/l) as a 4-min pulse at a concentration of 0.1 nmol/l. GnRH-induced LH release was reduced to 66% of its value by leukotriene (LT) B4 (0.1 nmol/l) action; also to 54% by LTC4, 66% by LTD4 and 74% by LTE4 action. In contrast, arachidonic acid (50 pmol/l) and its other 5-lipoxygenase metabolites: 5-hydroperoxyeicosatetraenoic acid (5-HPETE) (50 pmol/l), or 5-hydroxyeicosatetraenoic acid (5-HETE) (50 pmol/l), had no inhibitory effect on GnRH-induced LH release. Arachidonic acid and 5-HETE potentiated GnRH-induced LH release up to 249% and 429%, respectively, when applied in parallel with GnRH (1 nmol/l) as a 4-min pulse at a concentration of 10 pmol/l. In our earlier work we have shown that several leukotrienes are potent stimulants of LH release. The present report documents the finding that the 5-lipoxygenase pathway is also involved in the inhibitory regulation of hormone release in anterior pituitary cells.

Acute dopaminergic blockade augments the naloxone-induced LH rise in estrogen-treated postmenopausal women

OBJECTIVES

To assess the effect of estrogen replacement on the simultaneous blockade of the dopaminergic (DA) and opioidergic neural control of hypothalamic-gonadotropic function in postmenopausal women.

METHODS

Twenty healthy postmenopausal women, 48-55 years old were randomly assigned to receive either a 4-h naloxone infusion at 2 mg/h (group 1, n = 7) or a 10 mg i.v. bolus of metoclopramide (group 2, n = 7) or both drugs, simultaneously (group 3, n = 6) before and after 3 weeks of transdermal estradiol (100 microg/day). Blood samples were obtained at 30-min intervals during 4 h and duplicate determinations of serum follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E2) and prolactin (PRL) were performed in all samples.

RESULTS

In group 1 only a mild but significant LH rise after but not before estrogen replacement was seen. In group 2 PRL had a greater rise after than before estrogen therapy, without other hormonal changes. In group 3 a greater rise in PRL occurred after than before estrogen administration and serum LH had a sustained rise throughout the test only after estrogen replacement (greater than in group 1). No FSH changes were observed. The after-estradiol PRL response was nearly similar in groups 2 and 3.

CONCLUSIONS

Our results indicate that in the untreated postmenopausal women, the dopaminergic system has little and the opioidergic system has no significant input in the control of gonadotropin or prolactin release. However, following estrogen replacement, opioids are involved in the inhibition of LH release and stimulating PRL release, while the dopaminergic system acts to inhibit PRL release and modulates LH release or inhibition, depending on the levels of circulating estrogens.

LH isoform profiles during short-term pulsatile LHRH administration in elderly men

LH isoform profiles were analyzed in sera resolved with isoelectrofocusing from 5 elderly men (age 70.6 +/- 2.95) and 5 young adult men (age 28.2 +/- 1.24), by using polyclonal antibodies (RIA), monoclonal antibodies directed against the beta-subunits (IRMA) and in vitro LH bioassay. Despite the fact that the elderly had lower testosterone levels than the young (293 +/- 38 vs 512 +/- 77 ng/dl, p < 0.05), no differences were noted in the isoforms detected by any of the assays, although each assay yielded a characteristic profile. Indeed, RIA showed most LH in the acidic range, while IRMA revealed LH profiles with a major peak in the basic range, thus resembling the profiles determined by means of the bioassay. In the elderly, the profiles were also analyzed on day 7 and day 14 of short-term pulsatile sc LHRH administration (150 ng/bw/120 min). Only the LH bioassay detected an LHRH-induced shift to more basic and bioactive forms; these changes accompanied an increased in testosterone levels on day 7 (396 +/- 83 ng/dl, p < 0.05 vs day 0) and on day 14 (320 +/- 58 ng/dl NS vs day 0). Our data suggest that: 1) the profiles obtained in young and elderly subjects are similar, irrespective of the antisera used; 2) as a result of treatment with LHRH in the elderly an increase in T levels occurs, possibly due to the observed changes in LH bioactivity; 3) the in vitro LH bioassay appears to be the most sensitive assay in detecting such changes, which consisted of an enrichment in more basic and bioactive glycoforms.

Evidence for an interaction between alpha-MSH and opioids in the regulation of gonadotropin secretion in man

Gonadotropin secretion is inhibited by the endogenous opioids and stimulated by their antagonist naloxone. LH secretion is stimulated by alpha-MSH, a tridecapeptide derived from the post-translational processing of POMC. The possibility that alpha-MSH interacts with the opioids, as suggested by the experimental evidence, was investigated in 7 normal males aged 24-29 through the performance of seven tests: naloxone (0.8 mg i.v. bolus, followed by infusion of 1.6 mg/h for 120'); alpha-MSH (2.5 mg i.v. bolus); naloxone + alpha-MSH (2.5 mg i.v. 15' after commencement of the naloxone infusion); naloxone + GnRH (100 micrograms i.v. 15' after commencement of the naloxone infusion); alpha-MSH + GnRH (respectively 2.5 mg and 100 micrograms at time 0), GnRH alone (100 micrograms at time 0), placebo (150 nmol/l NaCl solution). The LH AUCs during both naloxone (30.3 +/- 2.7 mIU/ml.min-1) and alpha-MSH test (32.9 +/- 4.6 mIU/ml.min-1) were significantly greater (p < 0.005) than that observed during placebo (16.9 +/- 3.6 mIU/ml.min-1). The LH AUC during alpha-MSH + naloxone (37.6 +/- 2.6 mIU/ml.min-1) was not significantly different from that recorded during their separate administration. GnRH injected alone, during the naloxone infusion and with alpha-MSH produced similar increases in LH, that were significantly higher than that observed during the other tests (AUCs: GnRH 89.4 +/- 10.6, GnRH + naloxone 100.5 +/- 9.1, GnRH + alpha-MSH 94.6 +/- 7.9 mIU/ml.min-1, p < 0.001). Significant increase in FSH (p < 0.001) was only observed during GnRH, GnRH + naloxone and GnRH + aMSH tests (AUCs: placebo 13.3 +/- 1.7; naloxone 14.7 +/- 2.5; alpha-MSH 15.5 +/- 2.3; alpha-MSH + naloxone 16.9 +/- 1.9; GnRH 19.1 +/- 1.1; GnRH + alpha-MSH 20.7 +/- 1.3; GnRH + naloxone 21.2 +/- 1.8 mIU/ml.min-1). These results are in line with the possibility of an interaction between alpha-MSH and the opioids in the regulation of gonadotropin secretion, perhaps with opposing effects on a final common pathway.

Effect of progesterone pre-treatment on steroid secretion rates and follicular fluid insulin-like growth factor-1 concentrations in seasonally anoestrous ewes treated with gonadotrophin releasing hormone

Progesterone priming is known to prevent premature luteal regression in seasonally anoestrous ewes induced to ovulate with small dose multiple injections of gonadotrophin releasing hormone (GnRH), but the precise mechanisms involved are poorly understood. The main objective of the present study was to investigate the effect of progesterone priming, before and after a period of treatment with GnRH, on the biochemical activity of ovarian follicles collected from seasonally anoestrous ewes. Ewes in Groups 1 and 2 (6 ewes/group) received progesterone priming or vehicle alone, respectively, and were slaughtered 72 h later. Ewes in Groups 3 and 4 (6 ewes/group) were similarly primed with progesterone or vehicle only, respectively, and then 72 h later received 2-hourly injections of 250 ng GnRH for 20 h, followed 2 h later by a single bolus injection of 300 micrograms GnRH. They were then slaughtered 2 h after the bolus injection. All normal growing follicles > or = 2.0 mm diameter were dissected from the ovaries of all ewes and after measurement of their diameter, were incubated in Eagle's Basal Medium for 2 h to measure their steroid secretion rates. The fluid from each follicle was then aspirated and assayed for total insulin-like growth factor-1 (IGF-1) content. The luteinizing hormone receptor content of the whole follicle was estimated using 125I-labelled human chorionic gonadotropin (hCG). The follicles were classified as either non-oestrogenic or oestrogenic if their oestrogen production rate was < or = 300 or > 300 pg/ml/2h, respectively. The mean diameter of oestrogenic follicles (5.72 +/- 0.25 mm) was significantly (P < 0.001) larger than that of non-oestrogenic ones (3.93 +/- 0.25 mm). The mean numbers of oestrogenic and non-oestrogenic follicles were not significantly different among the four treatment groups. Oestradiol production rate was significantly (P < 0.001) increased as a result of GnRH treatment, but only in large oestrogenic follicles. Testosterone production rate was, however, significantly (P < 0.05) increased by both GnRH and progesterone in both classes of follicle. While GnRH treatment tended to decrease IGF-1 concentrations in small non-oestrogenic follicles, it significantly (P < 0.05) increased concentrations in large oestrogenic ones. IGF-1 concentrations were, however, significantly (P < 0.05) increased in both classes of follicle collected from progesterone-primed ewes treated with GnRH. Regardless of treatment, follicular fluid IGF-1 concentrations were significantly (P < 0.001) higher in small non-oestrogenic follicles compared to large oestrogenic ones. An increase in 125I-hCG binding to large oestrogenic follicles was observed in response to progesterone (P-0.07) in GnRH treated ewes. These results indicate differences in the biochemical activity of follicles attributable to progesterone priming which may be casually related to defective luteal function after ovulation.

Effects of low steroid doses administered in the mid and late follicular phase on the LH surge, ovarian steroids and follicular maturation in eumenorrheic women

The effects of four low doses of synthetic steroids, administered orally and starting on day 8 (group I) or on day 10 of the menstrual cycle (group II), upon LH surge, ovarian steroidogenesis, follicular maturation and menstrual cycles were studied in 10 eumenorrheic women. The results revealed that the day before the LH surge, the highest level of estrone-3-glucuronide was observed in both groups. Twenty-four hours after the last dose, the maximum urinary LH levels were recorded in groups I (day 11), and II (day 13). Pregnanediol-3 alpha glucuronide remained low during the study in group I, whereas in group II a gradual rise of this hormone starting on day 13 was registered and the highest level was found at day 21 of the menstrual cycle. Follicular maturation and ovulation were observed only in women from group II. Short and normal length cycles were recorded in groups I and II, respectively. In summary, low doses of exogenous synthetic steroids administered on day 8, but not on day 10 of the cycle, inhibit follicular maturation and ovulation.

Influence of an antiprogestin (onapristone) on in vivo and in vitro fertilization

The effects of a progesterone antagonist (onapristone) on heat synchronization, luteinizing hormone (LH) surge, ovulation, oocyte maturation and fertilization of superovulated ewes were studied. Its effects on in vitro bovine oocyte maturation and fertilization were also studied. Estrus synchronization and superovulation treatments were applied to 39 adult ewes using an intravaginal sponge with fluorgestone acetate for 9 days with injections of prostaglandin F2 alpha and pregnant mare's serum gonadotrophin given 24 h before sponge withdrawal. The animals were randomly assigned to four different groups; T1 receiving only the synchrony treatment (n = 11); T2 ewes received two injections of onapristone (1 mg kg-1, i.v.) 12 h apart from 3 h after sponge withdrawal (n = 10); T3 ewes received two injections of progesterone 12 h apart from sponge withdrawal (n = 10); and, T4 ewes received both onapristone and progesterone as described (n = 8). Ewes were mated by a fertile male during estrus. Progesterone and LH were measured during the superovulation period in plasma samples taken every 4 h. Uterine flushings for ova recovery were performed at 5 days (n = 25), 48 h (n = 5) and 24 h (n = 5). Non-fertilized oocytes collected at 24 and 48 h were checked for meiosis resumption. The effects of two doses of onapristone (D1 and D2) on in vitro bovine oocyte maturation (control = 100, D1 = 100 and D2 = 100) and fertilization (control = 107, D1 = 40 and D2 = 75) were also studied. The percentage of animals showing heat signs was significantly lower in group T3 (50% vs. 100%). The onset of oestrus (27.6, 24.8, 68.8 and 25.5 h, respectively for T1, T2, T3 and T4) and an LH surge (32.3, 28.8, 76.5 and 30.5 h, respectively for T1, T2, T3 and T4) after sponge withdrawal were significantly delayed in group T3. There were no significant differences in the intervals between estrus and LH surge among groups (4.61 +/- 0.75 h). The response and ovulation rates until 40 h after sponge withdrawal (group T3 excluded) were similar among groups, but the fertilization rates were significantly lower in groups T2 and T4 when compared with T1 (2% and 3% vs. 41%, respectively; P < 0.001) due to sperm arrest in the cervix. Ova recovery rate decreased significantly from 24-48 h to 5 days and was not affected by treatments (76.9% vs. 37.1% respectively). Onapristone did not affect the resumption of meiosis. Fertilization of bovine oocytes in vitro decreased significantly only in group D2 when compared to control (48% vs. 62.6%, respectively). In conclusion, onapristone treatment during the preovulatory period did not interfere with normal synchronization of estrus, ovulation and oocyte maturation but severely compromised fertilization by arresting spermatozoa in the cervix.

Somatostatin receptor subtype specificity in human fetal pituitary cultures. Differential role of SSTR2 and SSTR5 for growth hormone, thyroid-stimulating hormone, and prolactin regulation

Somatostatin (SRIF), a hypothalamic inhibitor of pituitary growth hormone (GH) and thyroid-stimulating hormone (TSH) secretion, binds to five distinct receptor (SSTR) subtypes. We therefore tested SSTR subtype-specific SRIF analogs in primary human fetal pituitary cultures (23-25-wk gestation) to elucidate their role in regulating human pituitary function. Using reverse transcription-PCR, mRNA expression of SSTR2 and SSTR5 were detected in fetal pituitary by 25 wk. SRIF analog affinities were determined by membrane radioligand binding in cells stably expressing the human SSTR forms. GH secretion was suppressed equally (40-60%, P < 0.005) by analogs preferential for either SSTR2 (IC50 for receptor binding affinity, 0.19-0.42 nM) or SSTR5 (IC50, 0.37 nM), and compounds with enhanced affinity for SSTR2 were more potent (EC50 for GH suppression, 0.05-0.09 nM) than Lanreotide (EC50, 2.30 nM) and SRIF (EC50, 0.19 nM). Similarly, analogs with high affinity for SSTR2 or SSTR5 decreased TSH secretion (30-40%, P < 0.005). However, prolactin was effectively inhibited only by compounds preferentially bound to SSTR2 (20-30%, P < 0.05). Luteinizing hormone was modestly decreased (15-20%) by SSTR2- or SSTR5-specific analogs. An SSTR5-specific analog also exclusively inhibited GH in acromegalic tumor cells. Thus, SRIF regulation of GH and TSH in primary human fetal pituitary cells is mediated by both SSTR2 and SSTR5, both of which are abundantly expressed by 25 wk. In contrast, suppression of prolactin is mediated mainly by SSTR2. These results indicate that SSTR5 is critical for physiologic regulation of GH and TSH. SRIF analogs with selective affinity for this receptor may therefore be more effective in the treatment of hormone-secreting pituitary adenomas.

Tumor necrosis factor-alpha mediates endotoxin induced suppression of gonadotropin-releasing hormone pulse generator activity in the rat

Bacterial endotoxin lipopolysaccharide (LPS) is known to suppress gonadotropin secretion and this effect is assumed to be mediated by cytokines. In the present study, we examined whether LPS affected hypothalamic electrical activity associated with LH pulses, and whether tumor necrosis factor-alpha (TNF-alpha), a major cytokine induced by LPS, was involved in this process. Ovariectomized rats were fitted with chronically implanted electrode arrays in the mediobasal hypothalamus, and multiunit activity (MUA) was recorded under conscious, unrestrained conditions. Blood samples were withdrawn every 6 min through an indwelling atrial catheter or determining serum LH concentrations. Intravenous (i.v.) injection of LPS (1 microgram) suppressed characteristic increases (volleys) in MUA associated with LH pulses throughout the experimental period up to 5 h. This suppressive effect of LPS on MUA volleys was significantly attenuated by simultaneous intracerebroventricular (icv) injection of the antibody (50 ng) to TNF-alpha through an indwelling cannula in the lateral ventricle. These changes in MUA were faithfully reflected in the LH secretory pattern. Further, either i.v. (0.4-2 micrograms) or i.c.v. (20-250 ng) injection of TNF-alpha suppressed the frequency of MUA volleys and associated LH pulses in a dose-dependent manner. These results suggest that LPS leads to the suppression of gonadotropin-releasing hormone pulse generator activity through a mechanism involving TNF-alpha.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) increases release of luteinizing hormone and follicle-stimulating hormone from the pituitary of immature female rats in vivo and in vitro

Recent findings that serum levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were dramatically increased in weanling female Sprague-Dawley (S-D) rats treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) prompted a more detailed study to define the effect and to investigate its mechanism(s). Dose-response and time-course studies were performed in vivo. Single doses (0.03-30 micrograms/kg) of TCDD were administered orally by gastric intubation to 22-day-old female rats. Control animals received vehicle (corn oil) only, whereas naive controls were treated with an empty intubation syringe. Trunk blood was collected after decapitation at various time points during the subsequent 72 hr. Concentrations of LH and FSH were determined in serum by radioimmunoassays (RIA). Two distinct peaks of both hormones were detected. The first, at 1 hr, appeared to be a non-specific response to vehicle as it was present in both vehicle control and TCDD-treated animals, but not in naive control animals. The second peak, at 24 hr, occurred only in animals dosed with TCDD. Gonadotropin levels in these animals were dose-dependently elevated. The ED50 was about 5 micrograms/kg with a maximum elevation of 15- and 20-fold for LH and FSH, respectively. Subsequently, in vitro studies were conducted in cultured pituitary halves and in primary pituitary cell cultures exposed to gonadotropin releasing hormone (GnRH) and/or TCDD. The amount of LH released into the media was measured by RIA. TCDD caused a dose-dependent release of LH from pituitary halves with an ED50 of about 0.1 nM. This effect was abolished in calcium-free medium but was not attenuated by an GnRH antagonist. Further in vitro studies were conducted in primary pituitary cell cultures. Although the cells responded to GnRH very well, no effect of up to 100 nM TCDD on the release of gonadotropins was detected. The results suggest that TCDD induces dose-dependently a brief release of gonadotropins in immature female rats. This effect is at least partially due to an effect of TCDD in the pituitary. Increased release of gonadotropins as a result of TCDD treatment depends on the action of calcium but does not occur via activation of GnRH receptors. However, cells in a primary pituitary culture do not respond to TCDD with increased release of gonadotropins, suggesting that the effect of TCDD in the pituitary is mediated by a factor present in pituitary halves but not in primary cell culture.

Ovarian luteal cell toxicity of ethylene glycol monomethyl ether and methoxy acetic acid in vivo and in vitro

These studies define the site and mechanisms of reproductive toxicity of ethylene glycol monomethyl ether (EGME) in a nongravid female animal model using in vivo and in vitro methods. In vivo studies assessed vaginal cytology and histology, ovarian histology, and serum hormones in 80- to 90-day-old, adult, regularly cycling, female Sprague-Dawley rats treated daily with EGME or vehicle by oral gavage. Dose-response and time-course studies (four to nine rats per group per treatment) determined that 300 mg/kg EGME suppressed cyclicity without systemic toxicity within 3 to 8 days, and doses less than 100 mg/kg had no effect. Pathogenesis studies (six to nine rats per time and treatment) determined that 300 mg/kg EGME elevated serum progesterone within 32 hr after dosing, while serum estradiol, FSH, LH, and prolactin remained at baseline levels. In EGME-treated rats, cyclicity was suppressed, ovulation was inhibited, and corpora lutea were hypertrophied. Thus, EGME appeared to target the ovarian luteal cell. To further examine the toxicity in vitro, luteal cells were recovered from 23-day-old, hCG-primed Sprague-Dawley rats and treated with 0-10 mM methoxy acetic acid (MAA), the proximate toxic metabolite of EGME. MAA (1-10 mM) maintained elevated progesterone levels as production declined in untreated cells at 24 and 48 hr of culture. Progesterone production was maintained independent of LH-stimulated cAMP levels. MAA decreased ATP, but only at 48 hr and at 2.5 mM or greater concentrations. Thus, these studies establish that the ovarian luteal cell is a target of EGME and MAA in vivo and in vitro and that the effect on luteal cell progesterone production is likely independent of LH-stimulated cAMP pathways.

Alpha-adrenergic receptor antagonism and N-methyl-D-aspartate (NMDA) induced luteinizing hormone release in female rhesus macaques

The stimulatory influence of N-methyl-D-aspartate (NMDA), a glutamate receptor agonist, on LH secretion is well established in several mammalian species including the rhesus macaque. Although the mechanism of excitation appears to involve enhanced GnRH secretion, it is unclear whether the GnRH neurons respond directly to this excitation or whether stimulatory inter-neurons are involved. This study investigated the possibility that noradrenergic afferents play a major role in mediating the response of the primate hypothalamo-pituitary reproductive axis to NMDA. In situ hybridization histochemistry, using a cRNA probe coding for the NMDAR1 receptor subunit, revealed abundant mRNA in the locus coeruleus, a brain area rich in noradrenergic neurons. Furthermore, using double-label fluorescence immunocytochemistry, the tyrosine hydroxylase immunopositive neurons of the locus coeruleus showed immunoreactivity for the NMDAR1 receptor subunit protein. A second experiment examined whether prazosin, an alpha 1-adrenergic receptor antagonist, could attenuate NMDA-induced stimulation of LH release. Prazosin (either 1 or 5 mg/kg b.wt., i.v.) was administered to female rhesus macaques during the luteal phase of the menstrual cycle, 40 min before administration of NMDA (10 mg/kg b.wt., i.v.). Regardless of the prazosin pre-treatment, plasma LH concentrations showed a significant increase (P < 0.01) within 10 min of the administration of NMDA. Therefore, in spite of the evidence that at least some of the noradrenergic neurons of the primate hindbrain express the NMDAR1 receptor subunit, it is unlikely that noradrenergic inter-neuronal pathways alone play a major role in mediating the stimulatory action of NMDA on GnRH/LH secretion in primates. Indeed, because the GnRH neurons of the rhesus macaque are located diffusely in various regions of the hypothalamus and medial-septal/preoptic area, their net response to excitatory amino acids is likely to be more complicated, involving a combination of both stimulatory and inhibitory inter-neurons, and possibly also a direct interaction.