Regulation of steady-state luteinizing hormone messenger ribonucleic acid levels, de novo synthesis, and release by sex steroids in primary pituitarycell cultures of male African catfish, Clarias gariepinus

Primary pituitary cell cultures from sexually mature adult male African cat fish, Clarias gariepinus, were used to study the regulation of LH biosynthe sis by sex steroids. The cell cultures were exposed to testosterone (T), es tradiol (E-2), or 5 alpha-dihydrotestosterone (DHT), a nonaromatizable anal ogue of T, and to the likewise nonaromatizable 11-ketotestosterone (KT) and 11 beta-hydroxyandrostenedione (OHA), physiologically relevant androgens i n fish. Both T and E-2 elevated glycoprotein alpha (GP alpha) and LH beta s teady-state mRNA levels (quantified by RNase protection assay), de novo syn thesis (metabolic incorporation of radioactive amino acids and subsequent i mmune precipitation of LH), and release of preferentially newly synthesized LH, while DHT had no effect. inhibiting the aromatase activity abolished t he stimulatory effects of T. The effects of E-2 on LH mRNA levels and de no vo synthesis were dose dependent. Incubation with 10 ng/ml KT elevated GP a lpha and LH beta mRNA levels, while other concentrations of KT or all conce ntrations of OHA tested had no effect. The amount of newly synthesized LH, on the other hand, was decreased dose-dependently by OHA but not by KT. Sin ce this OHA-induced decrease did not change the specific activity (dpm immu ne precipitable [H-3]-LH/ng immune-reactive LH) of LH, we hypothesize that OHA exerted its effect by activating a crinophagic breakdown of secretory g ranules in catfish gonadotrophs. Electron microscopic examination of gonado trophs after in vitro exposure to 50 ng OHA/ml revealed that breakdown orga nelles had increased in size significantly. We conclude that the balanced p roduction of aromatizable (mainly stimulatory) and Ii-oxygenated androgens (mainly inhibitory) may be an important factor in regulating the amounts of LH available for secretion in male African catfish.