Spermatogonia of rainbow trout: II. In vitro study of the influence of pituitary hormones, growth factors and steroids on mitotic activity

At the present time, in spite of recent advances, knowledge about the facto rs regulating germ cell proliferation in the teleost testis is limited. Thi s study was designed to investigate, in vitro, the ability of various hormo nes, growth factors, and steroids to influence the proliferation of trout s permatogonia (Go) present in mixed cultures of somatic and germ cells prepa red from testes, either prespermatogenetic or spermatogenetic. The tested m olecules were usually present for the duration of culture (4.5 days) and H- 3-thymidine (H-3-Tdr) for the last day in culture. In our cell culture cond itions, homologous gonadotropin I (tGTH-I) and growth hormone (tGH) moderat ely stimulated H-3-Tdr incorporation by Go, with ED50 equal to 5.5 +/- 3.0 and 1.8 +/- 0.4 ng/ml respectively. Insulin growth factor I (rhlGF-I) and f ibroblast growth factor (rhFGF-2) stimulated H-3-Tdr incorporation by Go fr om spermatogenetic testes only, with ED50 equal to 16.2 +/- 9.3 and 2.4 +/- 0.3 ng/ml respectively. The effects of the most efficient concentrations o f rhlGF-I combined with those of either tGTH-I or tGH were additive. Sevent y to one hundred mu M suramin stimulated H-3-Tdr incorporation by Go from t estes at all maturation stages and this effect was additive with that of tG TH-I. We assume that this effect of suramin could result from the inhibitio n of an unidentified antimitogenic factor. No effect was observed with homo logous prolactin, human epidermal growth factor, activin a and B, transform ing growth factor-beta 1, testosterone, 11-ketotestosterone, 17 beta-estrad iol, pregnenolone, 11 beta-hydroxyprogesterone, and 22-hydroxycholesterol. In conclusion, our in vitro results suggest that GTH-I, GH, IGF-I, and FGF- 2, are potent in situ modulators of the proliferative activity of trout Go at the time of induction, speeding up, then slowing down spermatogenesis, t hrough direct or indirect additive and/or antagonistic influences. (C) 1999 Wiley-Liss, Inc.