R. Benz

Chronobiology of Prolactin Secretion in Women: Diurnal and Sleep-Related Variations in the Pituitary Lactotroph Sensitivity

While a nocturnal rise accounts for the marked circadian variability of prolactin (PRL) secretion in humans, the mechanisms subserving this neuroendocrine manifestation are still obscure. Since gonadotropin-releasing hormone (GnRH) stimulates PRL under physiological conditions, we questioned whether changes in the pituitary lactotroph sensitivity to GnRH during the 24-hour cycle may contribute to the expression of circadian PRL rhythmicity. Accordingly, 8 women were studied in the early follicular phase of their cycles (days 2-5) on 6 occasions in random order: during daytime between 10.00 and 14.00 h (day studies), at night between 22.00 and 02.00 h, when the women were awake (night studies), and finally, during the identical night hours, when the women were asleep (sleep studies). On all occasions, blood was collected at 10-min intervals for 4 h, while either GnRH (25 micrograms i.v. bolus) or saline (as control) was injected twice within 2 h. As assessed by the net PRL increments (differences between unstimulated nadir and stimulated peak) and the areas under the PRL response curves, the PRL secretion was not substantially altered following GnRH stimulations during the day studies. In contrast, PRL release was markedly enhanced (p < 0.05 or less vs. day studies), when GnRH was administered during the night studies. This GnRH-stimulated PRL release was even further increased (p < 0.01 vs. day, p < 0.05 vs. night or saline studies), when GnRH had been given during sleep.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic opioid antagonism on gonadotrophin and ovarian sex steroid secretion during the luteal phase

Since short‐term opioid antagonism increases LH pulsatility during the luteal phase in women, we postulated that prolonged opioid antagonism may also accelerate the LH secretory episodes at this time. If so, the functional and temporal links between secretory episodes of pituitary LH and oestradiol (E2) and progesterone (P) release from the mature human corpus luteum may be disrupted.

The human first-term placenta in vitro: Regulation of hCG secretion by GnRH and its antagonist

Gonadotropin releasing hormone (GnRH) has been proposed to play a role in the regulation of human chorionic gonadotropin (hCG) release from the human placenta. To test this assumption, we utilized an in vitro perifusion system, together with cultures of placental explants, to investigate short- and long-term effects of GnRH and its respective antagonist on the hCG secretion from the early human placenta. Tissue slices of human placenta (100 mg), obtained from first-trimester terminations of pregnancies, were continuously perifused and the effluent collected in fractions of 2-20 min. After initial perifusion periods of 30-40 min, either GnRH, a GnRH antagonist (SB-75; Asta Pharma, Frankfurt, Germany) or both compounds at equimolar concentrations were added to the perifusion medium at final concentration of 10(-4)-10(-8) mol/l). Administration was effected either continuously or intermittently in 10-min pulses. Further, 50-mg pieces of placental tissue explants were cultured in tissue culture plates for up to 6 days. During the perifusions, hCG (determined by enzymeimmunoassay) was found to be released spontaneously in a pulsatile fashion. Pulse amplitudes and frequencies of this episodic hCG secretion were increased in response to GnRH, but not affected by GnRH antagonist. Also, GnRH stimulated the hCG secretion during cultures of placental explants. When pharmacological doses of GnRH (10(-4) mol/l) were utilized, this stimulatory effect of GnRH was no longer evident, while perifusion with medium containing GnRH antagonist at identical concentrations stimulated the hCG secretion, indicating an intrinsic agonistic activity of the antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of androgens in the regulation of the human menstrual cycle

Although previous investigations have examined the importance of androgens in the regulation of the human menstrual cycle, no consensus has been reached, due to conflicting results. We have therefore used the non-steroidal anti-androgen flutamide as a pharmacological probe to evaluate the role of androgens in the control of gonadotropin secretion in normally cycling women. Eight women were studied during control and treatment cycles, during which either placebo (as control) or flutamide (750 mg orally) was given daily. Blood was sampled every other day during the follicular and luteal phases and daily around the expected midcycles for determination of luteinizing hormone (LH), follicle stimulating hormone (FSH), estradiol, progesterone and androgens (testosterone, androstenedione, dehydroepiandrosterone sulfate) by radioimmunoassay and immunoradiometric assay. To establish unstimulated and gonadotropin releasing hormone (GnRH)-stimulated gonadotropin profiles, blood samples were frequently collected (every 10 min for 8 h, GnRH 25 micrograms i.v. after 7 h on day 10 in both the control and treatment cycles. Compared to control conditions, the durations of both the follicular and luteal phases did not change considerably during flutamide treatments. Serum androgen levels (testosterone, androstenedione, dehydroepiandrosterone sulfate) were significantly (p < 0.01) reduced during androgen antagonism. Daily gonadotropin and estradiol levels did not differ between control and flutamide cycles, while progesterone secretion tended to be attenuated (p = 0.2) during the luteal phases of the flutamide cycles. The LH and FSH secretory profiles and the GnRH-stimulated gonadotropin responses remained virtually unchanged during androgen antagonism.(ABSTRACT TRUNCATED AT 250 WORDS)

How do androgens affect episodic gonadotrophin secretion in postmenopausal women

In the absence of any significant ovarian oestrogen secretion, as in post-menopausal women, the hypothalamic-pituitary axis may still be influenced by the androgens which continue to be produced. The episodic secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by postmenopausal women was accordingly assessed following short-term androgen antagonism induced by flutamide, a specific androgen receptor blocker. Blood samples were collected at 10-min intervals for 10 h in nine women before and during flutamide administration (750 mg/day for 6 days) for the determination of gonadotrophin and sex hormone concentrations by radioimmunoassay. On both occasions, 25 micrograms of gonadotrophin-releasing-hormone (GnRH) was injected intravenously 8 h after initiation of the blood collections. Flutamide administration decreased (P less than 0.01 or less) androgen concentrations (testosterone, androstenedione and dehydroepiandrosterone sulphate) in relation to baseline values, but did not alter oestrogen (oestrone and oestradiol) or sex-hormone-binding globulin levels. The LH and FSH pulse characteristics (frequency, amplitude, interpulse interval and transverse mean levels) determined by a cluster algorithm in the gonadotrophin secretory profiles did not differ before and during androgen blockade. By contrast, androgen antagonism increased LH (P less than 0.01) and tended to enhance FSH (P = 0.10) FSH release in response to GnRH stimulation. Hence, short-term androgen receptor blockade with flutamide did not greatly affect episodic gonadotrophin secretion. However, the combined evidence of the enhanced gonadotrophin release observed in response to GnRH stimulation and the unchanged gonadotrophin secretion during androgen antagonism suggests that alterations in the magnitude, but not the frequency, of hypothalamic GnRH release had occurred. Even in the presence of substantial serum androgen concentrations, the gonadotrophin pulse rhythm in hypogonadal women constitutes the maximal-rate GnRH-LH release pattern.

Human chorionic gonadotropin secretion from the early human placenta: In vitro regulation by progesterone and its antagonist

Local actions of placental neurohormones and sex steroids have been proposed to play a role in the regulation of human chorionic gonadotropin (hCG) release from the human placenta. Accordingly, we utilized an in vitro perifusion system and cultures of placental explants to investigate short- and long-term effects of progesterone and its respective antagonist on hCG secretion from the human first-trimester placenta. Tissue slices (100 mg) obtained from legal pregnancy terminations of 9-12 weeks of gestation were continuously perifused and the effluent collected in fractions of 2-20 min. After initial perifusion periods of 30-140 min, either progesterone, a progesterone antagonist (ZK 98-299), or both were added to the perifusion medium at final concentrations of 10(-4)-10(-9) mol/l. Administration was either continuous or intermittent in 10-min pulses. Furthermore, 50-mg pieces of placental explants were cultured in multiwell tissue culture plates for up to 5 days. During the perifusion studies, hCG (determined by enzyme immunoassay) was released in a pulsatile fashion. This hCG pulsatility was decreased in response to both progesterone and progesterone antagonist at all concentrations tested. In contrast, intermittent administration of either treatment increased the hCG secretion. Secretion of hCG was not affected when progesterone and its antagonist were co-administered at equimolar concentrations. These observations demonstrate the diverging effects of progesterone and its antagonist on hCG secretion from the human first-trimester placenta in vitro, depending on the experimental conditions. Thus, progesterone-modulated hCG secretion appears to be regulated in a complex manner, its fine tuning involving other, as yet uninvestigated intraplacental factors.

Pituitary gonadotropin responsiveness to repeated gonadotropin releasing hormone (GnRH) stimulations in patients with chronic anovulation

To evaluate whether repeated gonadotropin releasing hormone (GnRH) stimulations were superior to single GnRH administrations for the accurate assessment of pituitary gonadotropin responsiveness, the GnRH-stimulated luteinizing hormone (LH) and follicle stimulating hormone (FSH) responses of 49 hyperandrogenic patients (HA) were compared with those of 20 hypogonadotropic patients (HH) and of 24 normally cycling women (N). Blood samples were obtained at frequent intervals during GnRH administrations (25 micrograms twice within 2 h). Unstimulated LH concentrations were higher (p less than 0.001) in HA than in N and HH women. However, basal FSH levels differed only in HA from HH women (p less than 0.001). Following either GnRH stimulation, increased (p less than 0.01) LH and FSH releases were noted in all N, HA and HH women. The GnRH-stimulated LH and FSH responses to either GnRH injections were highest (p less than 0.01) in HA and lowest (p less than 0.01 vs. N) in HH women. The net LH and FSH increases over unstimulated concentrations (delta LH or FSH) in response to either GnRH stimulation were highest (p less than 0.01 or less) in HA women. By contrast, no differences were determined in the delta LH and FSH levels between the first and second GnRH stimulations within each group. These observations document different unstimulated and stimulated gonadotropin concentrations in normal cycling and anovulatory women. Gonadotropin responses to single GnRH administrations differ for anovulatory patients. Since the gonadotropin responses to the second GnRH stimulation are comparable to those during the first GnRH injections, repeated GnRH stimulations may not help to distinguish the degree of pituitary responsiveness in ovulatory from anovulatory women.

46 HUMAN CHORIONIC GONADOTROPIN RELEASE BY HUMAN TERM PLACENTA IS DYNAMICALLY REGULATED BY GLUCOSE

During gestation human chorionic gonadotropin (hCG) is secreted in an initial rise to maintain corpus luteum function. In early pregnancy, also spontaneous pulsatile hCG secretion regulated by a GnRH-like compound of placental origin has been described. -Question: Are there metabolic influences which regulates hCG release?Methods: Explants of human term placenta (500 mg) were perifused in 1 ml chambers (ACUSYST, Endotronics) with a flow rate of 100 ul medium 199/min. The glucose concentrations were changed from 5.55 to 0 mmol/l resp. 16.0 to 5.55 mmol/l in pulses of 16 min. The experiments lasted for 5 hours. HCG was measured every 4 min by IRMA.Results: 1. In hypoglycemic conditions, the lowered glucose concentration was followed by significant peaks (PULSAR analysis) of hCG reaching more than 40.9±25.2 % (mean + SD) of basal level (duration 6.1±1.8 min) (n=13). 2. Repeated lowering of glucose (max. 3 times) showed corresponding hCG bursts (height: 16 - 168 mlU/ml). 3. Decreasing glucose concentrations in -erifusate per se were answered by elevated hCG bursts (n=3).Conclusion: In vitro, human placenta reacts to diminished glucose supply with increased hCG release. This does not seem to be due to a total lack of fuel.-Supp. by DFG (Hel107/2-3)