Salmon gonadotropin (sGTH) immunoreactivity and 11-oxotestosterone secretion of mature rainbow trout (Salmo gairdneri) testes in vitro: an alternative to radio-receptor assay for sGTH-binding studies

After three intraperitoneal injections of salmon gonadotropin (sGTH) or bovine serum albumin (BSA), testicular tissue of fully mature rainbow trout was prepared for in vitro incubation with or without sGTH. The secretion of 11-oxotestosterone was measured and the tissue was fixed for light-microscopical localization of sGTH immunoreactivity (ir). Tissue from sGTH-treated males showed an increased basal secretion and sGTH-stimulated androgen secretion but the stimulated versus control ratio was higher without sGTH treatment in vivo. When the tissue had had contact with exogenous sGTH, sGTH-ir showed similar distribution patterns regardless of the sGTH treatment regimes. The extralobular compartment showed a staining of interstitial cells and capillary walls. The staining in the intralobular compartment was less clear. Many Sertoli-cells carried a faint nuclear label, whereas intralobular germ cells appeared to be unlabeled.