To test the hypothesis that FSH is secreted at least in part within discrete secretory bursts in women and that the characteristics of episodic FSH secretion are altered within differing gonadal hormone environments, we measured FSH by immunoradiometric assay every l0 min for 24 h in premenopausal women during the early folicular (EF), late follicular (LF), and midluteal (ML) phases of the menstrual cycle and in postmenopausal (PM) women (n = 8 in each group). Secretory events were evaluated using multiparameter deconvolution. FSH was secreted in an episodic manner, with the number of scoretory bursts (per 24 h; mean ± SEM) detected in LF (20 ± 0.79) and PM (20 ± 0.90) women being greater than that in EF (16 ± 0.88) and ML (14 ± 0.93) women. FSH secretory burst mass (milliinternational units per mL) was significantly higher in PM (12 ± 1.6) than in EF (1.8 ± 0.21). LF (3,1 ± 1.3), or ML (0.8 ± 0.11) women and primarily reflected a relative increase in the maximal secretory rate rather than increased burst half- duration. The estimated half-life (minutes) of endogenous FSH in LF women (155 ± 18) was shorter than those calculated in EF (251 ± 24>, ML (277 ± 38), and PM (231 ± 18) women. Cross-correlation analysis showed strongly positive associations between successively paired serum FSH and LH concentrations in all four groups of women. Deconvolution of simultaneously obtained LH concentration-time series revealed statistically significant concordance (13-25%) between FSH and LH secretory episodes at a lag time of 0 min in EF, LF, and PM women and when LH secretory bursts led FSH secretory bursts by 10 min in ML phase women. However, as 75-87% of FSH and LH secretory pulses were discordant, we infer the operation of distinct control mechanisms in the generation of FSH and LH release episodes. In summary, these results suggest that FSH is secreted within discrete secretory bursts in women, that the mass and frequency of FSH secretory bursts differ in women exhibiting various gonadal hormone environments, and that FSH and LH secretory bursts occur coincidentally at a higher rate than expected on the basis of chance alone, but at such a low overall rate of concordance that distinct mechanisms probably operate to direct episodic FSH and LH secretory activity.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism