Gonadotrophin releasing hormone pulse generator activity before and during sexual maturation in girls: new insights.

The activity of the gonadotrophin releasing hormone (GnRH) pulse generator during pubertal transition was investigated in 40 healthy girls 7-18 years of age. Ten were pre-pubertal, seven were in early puberty, and 23 were post-menarcheal. Serum concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured with immunofluorimetric assays, which have a sensitivity approximately 100-fold that of radioimmunoassay, in samples taken at 10-min intervals for 24 h during basal conditions, during Nal-Glu antagonist suppression, and in response to GnRH stimulation (10 micrograms). Serum levels of androstenedione, testosterone and oestradiol were measured by radioimmunoassay. Our data show that the GnRH pulse generator is functionally active in prepubertal girls with selective expression of LH and FSH pulses after the onset of sleep. The onset of puberty is associated with a greater increase in LH pulse amplitude than frequency. These overall changes are punctuated by a switch of wake/sleep activities of GnRH pulse generator with a progressive increase in day-time pulsatility and a gradual reduction of sleep-entrained amplification. While LH pulsatility appears to be highly GnRH dependent at all ages, a remarkable decrease in the predominance of GnRH regulation of FSH pulsatility occurs in conjunction with ovarian activation.