Potentiating Effect of Growth Hormone on Vitellogenin Synthesis Induced by 17β-Estradiol in Primary Culture of Female Silver Eel (Anguilla anguillaL.) Hepatocytes

Abstract

Previousin vivoexperiments have indicated a potentiating role of growth hormone (GH) during experimentally induced vitellogenesis by 17β-estradiol (E2) in the female silver eel (Anguilla anguillaL.). To investigate whether GH has direct hepatic actions, the effects of hypophysial-purified and recombinant GH on vitellogenin (Vg) synthesis in response to E2 were tested on primary cultures of hepatocytes. Hepatocytes were prepared from control or E2-primed eels. Addition of E2 alone into the culture medium induced both Vg synthesis and secretion in a dose- and time-related fashion. Bovine growth hormone (bGH) alone had no effect on the induction of Vg synthesis or secretion. Bovine GH enhanced thein vitroeffects of E2 on both Vg synthesis and secretion, an effect attenuated by anin vivoE2 priming which was dose-dependent with an ED50of 5 ng/ml. To investigate the specificity of GH action, purified eel and salmon GH and salmon, trout, and tilapia prolactins (PRL), as well as recombinant trout and tilapia GH, were tested, and the responses were compared to bGH. Purified salmon and homologous eel GH potentiated the vitellogenic response to E2. Recombinant GH were highly efficacious, excluding the presence of active contaminants in the potentiating effect of GH preparations. The potentiating effect of recombinant trout GH on the vitellogenic response was reduced at high doses (above 20 ng/ml), suggesting a down-regulation of GH binding sites by GH itself. Salmon PRL has minimal activity, but not trout and tilapia PRL, indicating that PRL is not an important potentiating factor on Vg synthesis in our model. It is concluded that GH acts directly on the liver to potentiate E2 induction of eel hepatic Vg synthesis. The potentiating effect of GH appears to be time- and dose-dependent and modulated as a function of hormonal status (E2 priming) of the eel.