Hormonal dynamics during luteal-follicular transition.

To gain insights into the neuroendocrine basis for the initiation of folliculogenesis, the hormonal dynamics during the period from the late luteal to the early follicular phase of the menstrual cycle (the luteal-follicular transition) were examined. Blood samples were obtained at 2-h intervals for 5 consecutive days in seven women and at 15-min intervals for 8 h on each of 4 consecutive days in five women. The results indicate that the luteolytic process, as reflected by an exponential decline of both serum estradiol and progesterone levels, began at least 64 h before the onset of menses. During estradiol and progesterone withdrawal, there was a selective increase in mean serum FSH levels (P less than 0.001) beginning 24 h before and reaching a peak 24 h after the onset of menses. The frequency of LH pulses increased slightly but not significantly during this period, with a significant rise in mean serum LH levels on the day of menses. Thus, an acute rise in FSH concentrations the day before and in LH concentrations the day after the onset of menses occurs during luteal-follicular transition. The dissociation of FSH and LH secretion observed suggests that additional neuroendocrine events other than changes in pulsatile GnRH secretion may be operative during this period. These findings indicate that the initiation of folliculogenesis for the ensuing cycle occurs during the late luteal phase by a process of selective augmentation in FSH secretion independent of hypothalamic GnRH secretion. This event may ultimately prove to be a manifestation of the action of recently characterized ovarian peptides on FSH secretion

The dependency of folliculogenesis and corpus luteum function on pulsatile gonadotropin secretion in cycling women using a gonadotropin-releasing hormone antagonist as a probe.

A potent GnRH antagonist, [Ac-delta 3-Pro1,p-F-D-Phe2,D-Trp3,6]GnRH (4F-Antag), was used as a probe to determine the relative dependency of ovarian cyclicity on pulsatile gonadotropin secretion. 4F-Antag was administered in a dose of 80 micrograms/kg sc twice a day for 3 consecutive days during different phases of the menstrual cycle. This treatment resulted in a prompt attenuation of pulsatile gonadotropin secretion in all women studied. Maximal suppression of gonadotropin levels, expressed as percent change from baseline, averaged 48% for LH and 22% for FSH. The reduced pulsatile gonadotropin release induced by 4F-Antag administration during the early follicular phase resulted in a significant decrease in serum estradiol levels during the period of treatment and was followed by a prolongation of follicular phase (2.4 days) and cycle length (3.5 days), but no alteration of subsequent cyclic ovarian steroid profiles compared to control cycles. Treatment initiated during the midfollicular phase 4-6 days before the expected LH surge resulted in a more dramatic decline in serum estradiol levels and prolongation of follicular phase length by 5-6 days compared to control cycles. Normal luteal function was preserved. These alterations were compatible with induction of the demise of the dominant follicle followed by the reinitiation of follicular recruitment. Administration of 4F-Antag during the midluteal phase resulted in rapid falls in serum estradiol and progesterone levels and the onset of menstrual bleeding in all women. The luteolytic effect of 4F-Antag was completely negated by the administration of hCG. These data indicate that 4F-Antag interferes with ongoing cyclic ovarian function by reducing pulsatile gonadotropin stimulation, which disrupts folliculogenic processes and induces the demise of the corpus luteum. From these findings we infer that the functional integrity of ovarian cyclicity is remarkably sensitive to brief (3 days) and partial reduction in pulsatile gonadotropin secretion

FREQUENCY OF PROLACTIN PULSATILE RELEASE IN NORMAL MEN AND IN AGONADAL PATIENTS IS NEITHER COUPLED TO LH-RELEASE NOR INFLUENCED BY ANDROGEN MODULATION

OBJECTIVE We wished to examine and characterize the prolactin pulsatile secretory pattern in both normal and agonadal males in order to assess whether there was any concordance with LH secretion. DESIGN Patients were sampled every 5 minutes for 12 hours. PATIENTS We studied five normal and four agonadal men, the latter group before and on testosterone enanthate (TE) (200 mg i.m. every 15 days) treatment. MEASUREMENTS Prolactin and luteinizing hormone plasma levels were determined using commercial RIA systems. Pulse detection was performed using the DETECT program and the degree of concordance between luteinizing hormone and prolactin was established computing the specific concordance index. RESULTS We demonstrated the presence of a frequent PRL secretory pattern in normal men (22.8 +/- 1.8 peaks/12h; mean +/0 SEM) and in agonadal patients, both in basal conditions and during testosterone treatment (20.5 +/- 2.8 and 18 +/- 1.6 peaks/12h, respectively). The testosterone treatment in agonadal men significantly reduced luteinizing hormone pulse frequency (baseline: 27.5 +/- 2, testosterone administration: 18 +/- 1.3 peaks/12h, P < 0.01) but did not affect pulsatile prolactin release. Using a 10 and 15 minute sampling protocol, we observed that prolactin pulse frequency significantly decreased (P < 0.01) and was similar to the frequencies estimated in previous reports. When luteinizing hormone and prolactin time series were studied to evaluate the possible presence of a specific concordance (SC) between the secretory events of the two hormones, no significant degree of concomitancy was observed neither using the specific concordance index or the cross-correlation analysis. CONCLUSONS This report demonstrates (a) the presence of frequent pulsatile release of prolactin in both controls and agonadal patients (baseline and on testosterone enanthate), (b) the use of an appropriate sampling interval (5 minutes) to unmask the prolactin pulsatile release, (c) that in men, luteinizing hormone secretory events are not temporally linked to prolactin secretion, and (d) that androgens, even if reducing luteinizing hormone pulse frequency in agonadal patients, do not significantly affect prolactin pulsatile secretion, suggesting that testosterone and its metabolites do not affect lactotroph activity