Pulsatile release of bioactive luteinizing hormone in prepubertal girls: Discordance with immunoreactive luteinizing hormone pulses

An assessment of pulsatile secretion of luteinizing hormone (LH), measured by both immunoassay (I-LH) and rat interstitial cell testosterone production bioassay (B-LH), as well as of folicle-stimulating hormone and glycoprotein hormone α-subunit was carried out in seven normal prepubertal and six normal premenarcheal pubertal girls. Samples were obtained at 20-min intervals for a 6-h period. The hormone secretion profile were analyzed by several computerized methods yielding pulse frequency and amplitude, interpulse basal levels, and percentage increments, with bio/immuno ratios calculated for peak and basal concentrations. In these prepubertal girls, mean B-LH levels were 12% of I-LH, with B/I ratio of 0.13; 30% of samples were below assay sensitivity (0.10 mIU/ml) for B-LH, but all I-LH (1.25 mIU/ml) were detectable. In the pubertal group, B-LH levels were 30% of I-LH, with mean B/I ratio of 0.24 and undetectable B-LH in 29% of samples. Pulsatile secretion in prepubertal girls was found in five of seven (1/150 min) for B-LH and six of seven (1/212 min) for I-LH; only two of six pubertal girls had detectable pulses. Discordance of B- and I-LH pulses were frequent, with 56% of B-LH pulses lacking an I-LH pulse and 47% of I-LH pulses not having a B-LH pulse. These data demonstrate that 1) both B- and I-LH are secreted episodically in prepubertal girls; 2) I-LH-like material is present in higher concentrations than B-LH in these girls; and 3) substantial discordance of B- and I-LH pulses exist. Such findings lend further support for molecular heterogeneity of pituitary gonadotropins during the pubertal process and suggest that changes of biopotency may be important functional regulators of the early pubertal process.