Secretion of inhibin B by human prepubertal testicular cells in culture

Objective: Inhibin B is a secretory product of Sertoli cells of the human testis. 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 study was to evaluate inhibin B secretion in primary prepubertal mixed testicular 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-day-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/ml 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 triplicate. Inhibin B was determined by ELISA and testosterone by RIA. Results: Median (range) inhibin B secretion was 465 (225-1007), 275 (107-298), 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 data. Mean +/- S.D, of transformed inhibin B secretion in group 1 was significantly 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 significant correlation between testosterone and inhibin B secretion into the medium was found when the 22 culture samples were analyzed as a whole. Inhibin B secretion was significantly increased after stimulation with highly purified hLH, rhFSH and rhGH (P < 0.05) and a significant positive correlation between inhibin B and testosterone was found under both hLH and rhFSH stimulation. Conclusions: It is concluded that cells collected from newborns have the highest capacity to secrete inhibin B in vitro, and that this capacity decreases 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 high newborn values. As expected, FSH stimulated inhibin B secretion in culture. LH stimulation was probably mediated by paracrine factors secreted by interstitial cells. Finally, our results add new evidence of the involvement of GH in testicular maturation.