EVIDENCE SUGGESTING AN ADDITIONAL CONTROL MECHANISM REGULATING EPISODIC SECRETION OF LUTEINIZING-HORMONE AND FOLLICLE-STIMULATING-HORMONE IN PRE-PUBERTAL CHILDREN AND POSTMENOPAUSAL WOMEN

The possible differential regulation of pulsatile follicle stimulating hormone (FSH) and luteinizing hormone (LH) secretion in pre-pubertal children and in post-menopausal women was investigated. Children were studied for 4 h and post-menopausal women for 6 h; blood samples were taken every 10 min. Post-menopausal women were studied before and 21 days after administration of a single i.m. dose of gonadotrophin-releasing hormone (GnRH) analogue. Eight post-menopausal women and 18 children (nine boys and nine girls) were enrolled, The children were divided into two groups: A, at Tanner stages 0-1 (four boys and three girls); B, at Tanner stage 2-3 (five boys and six girls). Plasma LH and FSH concentrations were determined using an immunofluorimetric assay. Time series were analysed and the specific concordance (SC) index was computed to determine the degree of concordance between episodes of LH and FSH secretion. While children of group A had LH concentrations below the minimal detectable dose of 0.1 IU/l, group B showed measurable LH plasma concentrations (1.4 +/- 0.3 IU/l, mean +/- SEM). Plasma FSH concentrations were detectable in both groups. Group A showed FSH plasma concentrations significantly lower than those of group B (0.75 +/- 0.2 and 1.95 +/- 0.4 IU/l respectively; P < 0.05), but FSH pulse frequency was higher in group A (P < 0.05). Children of group B showed significant concomitance of LH and FSH secretory events at time 0 (P < 0.05). Past-menopausal women showed both LH and FSH plasma concentrations to be reduced after GnRH analogue administration (P < 0.01), but only LH pulse frequency, not FSH pulse frequency, was significantly decreased (P < 0.01). In these patients LH and FSH were co-secreted before (P < 0.05) but not after GnRH analogue administration. In conclusion, this study confirms that during pre-puberty FSH is episodically secreted while LH is not. Following pubertal development, plasma LH concentrations increase and pulses of the two gonadotrophins are synchronized. The co-secretion of LH and FSH is also observed in post-menopausal women, but not after the single administration of a GnRH analogue. These data suggest that FSH might have an additional stimulatory pathway that is independent of GnRH.