Abstract 19

Three peaks in serum testosterone (T) levels have been described in the developmental history of human Leydig cells: during fetal life, post-natally peaking at 2-3 months and at puberty. The endocrine and paracrine regulation of the postnatal activation and subsequent quiescence of the prepubertal human testis is poorly understood. We have developed an experimental model of culture of human testicular cells isolated from testes collected at necropsy to study this regulation. We had reported an age dependent difference in basal testosterone secretion: the 1- to 7-month-old group (G2) had higher levels than the 12- to 36-month-old group (G3) and, furthermore, it did respond to hLH, hFSH and hGH stimulation (Pediatric Research 38:592-597, 1995). In this report we have studied the effect of 50 ng/ml rlGF1 in these groups and in a younger group of 4- to 10-day-old newborns (G1). Isolated testicular cells were maintained in culture for 6 days in the absence or in the presence of hLH or rlGF1, and T, androstenedione (Δ), and dehydroepiandrosterone (D) were determined by RIA. 3β-HSD and 17β-HSD were estimated from the ratios (T + Δ)/D and T/Δ respectively. Response to stimuli was expressed as % over basal condition. While rlGF1 stimulated T secretion in G1, G2 and G3 (X ±SD:391±85.8, n=8, and 277±214%, n=5, respectively, p<0.05) hLH did so only in G2 (532±563%, n=8, p<0.05). The effect of rlGF1 was dose dependent. Similarly, rlGF1 stimulated 3β-HSD in G1 and G2 (255±63, n=3, and 636±381%, n=6, respectively, p<0.05), while hLH did so only in G2 (369±288%, n=7). No significant effect was observed in 17β-HSD with hLH nor with rlGF1 in either age group. It is concluded that IGF 1 is a modulator of testosterone biosythesis during the postnatal activation of the human testis. The action is probably mediated at the level of 3β-HSD, but effects at other levels cannot be rules out.