Comparison of pulsatile luteinizing hormone secretion between prepubertal children and young adults: evidence for a mass/amplitude-dependent difference without gender or day/night contrasts.

The assessment of pulsatile GnRH activity in children has become possible since the introduction of the sensitive third generation immunochemiluminescent assays, permitting detection of previously unmeasurable levels of LH and FSH. Despite this, however, studies differ with regard to pulse frequency and the presence of a diurnal variation in LH secretion in clinically prepubertal children. Discrepancies may reflect the limitations of relatively long intersampling intervals, less sensitive LH assays such as RIAs, and the use of algorithms to analyze pulsatile LH secretion, which do not account for endogenous production rates and metabolic clearance. To address this, we studied LH secretion in 10 prepubertal children (4 boys and 6 girls, age 8.5-10.8 y) and 12 young adults (7 men and 5 women in the early follicular phase, age 18.6-32.8 y). Blood was sampled every 5 min from 2000 h to 0200 h (nighttime) and from 0800 h to 1400 h (daytime) for LH determination, using an immunochemiluminescent assay. Deconvolution analysis revealed no difference between daytime and nighttime LH secretion, including LH secretory amplitude and pulse frequency, within any of the 4 groups, permitting pooling of the data from the 2 sampling intervals for analysis. In addition, there was no difference in LH secretion or half-life between genders. Comparison of pulsatile LH secretion between children and adults revealed a marked increase in the mass and amplitude of LH secreted per burst. LH secretory burst mass rose 9.5-fold in females, increasing the mean LH concentration by nearly 13-fold and the production rate by nearly 9-fold. The trend in males was similar although less remarkable, with a 4.2-fold rise in LH secretory burst mass from childhood to adulthood. No differences in pulse frequency, interburst interval, half-life, or approximate entropy were found between prepubertal children and adults. We conclude that the maturational change in LH secretion occurs via a highly specific mass/amplitude-dependent mechanism without significant gender or day/night differences.