Secretion of inhibin B by human prepubertal testicular cells in culture

Objective: Inhibin B is a secretory product of Sertoli cells of the human t estis. It has been reported that serum levels of inhibin B in infant boys, peaking at 3 months of age, exceed levels in adult men. The aim of this stu dy was to evaluate inhibin B secretion in primary prepubertal mixed testicu lar cell cultures, prepared from testes collected at necropsy. Design and Methods: Cell cultures were divided into three age groups on the basis of differences in testicular histology: group 1 (n = 7), 1- to 10-da y-old newborns, group 2 (n = 7), 1- to 9-month-old infants, and group 3 (n = 8), 12- to 84-month-old children. Cells were maintained in culture for 6 days, harvested and counted. In some samples, during the last 4 days, cells were stimulated with 10 ng/ml highly purified human (h) LH (n = 9), 2 ng/m l recombinant human(rh) FSH (n = 9) or 50 ng/ml rhGH (n = 4). On day 6, the secretion of inhibin B and testosterone into the medium was estimated in t riplicate. Inhibin B was determined by ELISA and testosterone by RIA. Results: Median (range) inhibin B secretion was 465 (225-1007), 275 (107-29 8), and 58 (15-184) pg/million cells,24 h in groups 1, 2 and 3 respectively . A logarithmic transformation of these values was performed to normalize d ata. Mean +/- S.D, of transformed inhibin B secretion in group 1 was signif icantly higher than in group 2 or 3 (P < 0.005) and the values for groups 1 and 2 were significantly higher than that for group 3 (P < 0.005). No sign ificant correlation between testosterone and inhibin B secretion into the m edium was found when the 22 culture samples were analyzed as a whole. Inhib in B secretion was significantly increased after stimulation with highly pu rified hLH, rhFSH and rhGH (P < 0.05) and a significant positive correlatio n between inhibin B and testosterone was found under both hLH and rhFSH sti mulation. Conclusions: It is concluded that cells collected from newborns have the hi ghest capacity to secrete inhibin B in vitro, and that this capacity decrea ses with age during the first years of life. Since no data are available on serum inhibin levels in newborns, it is possible that concentrations at 3 months of age do not represent a post-natal peak but a declining level of h igh newborn values. As expected, FSH stimulated inhibin B secretion in cult ure. LH stimulation was probably mediated by paracrine factors secreted by interstitial cells. Finally, our results add new evidence of the involvemen t of GH in testicular maturation.