Intrinsic secretory characteristics of luteinizing hormone and prolactin episodic release during pubertal development

The intrinsic characteristics of LH and prolactin (PRL) episodic secretion were evaluated in a group of 18 children (8M and 10F). The children were divided into two groups according to the Tanner stage: Group A (Tanner ≤ 1, N = 7, 3M and 4F, 6-10 years of age) and group B (Tanner 2-3, N = 11, 5M and 6F, 9-11 years of age). A pulsatility study of 4 h, sampling every 10 min, was carried out in all children. LH and PRL plasma levels were assayed by IFMA and RIA respectively. LH and PRL secretory episodes were then identified on plasma determinations using the program DETECT, Instantaneous secretory rates (ISR) were then computed for both LH and PRL using the specific algorithm within the DETECT program. Plasma LH levels were different between the two groups of children. Group A children showed undetectable LH plasma levels (below the minimal detectable dose of 0.1 mIU/ml), while group B demonstrated LH plasma levels in the normal range of values for age and sexual development (1.5 ± 0.3 mIU/ml, mean ± SEM). LH pulse frequency for group B was 3.2 ± 0.4 peaks/4h. No significant differences in mean plasma PRL levels, pulse frequency and pulse amplitude were observed between the two groups of children. Computation of ISR for LH (group B only) and PRL (both groups) identified the intrinsic episodic characteristics of the two hormones. No significant differences in LH and PRL pulse frequencies were observed when comparing the results estimated on ISR with those estimated on plasma concentrations. No significant changes in PRL pulse amplitude were observed between the two groups. Conversely, a shorter duration of LH and PRL secretory episodes was found. In conclusion, in children PRL, secretory bursts from lactotropes lasted the same number of minutes independently of the Tanner stages. Moreover, the LH secretory events were clearly detectable during the daytime only when puberty had already started. The duration of PRL and LH secretory events was similar to adult fertile subjects. These data indicate that the gonadal maturation does not modify LH and PRL secretory events from the pituitary.