Vasoactive peptides and phenylephrine actions in isolated teleost hepatocytes

The metabolic actions of the vasoactive peptides vasotocin and isotocin and the alpha-agonist phenylephrine are examined in hepatocytes isolated from three teleost species: brown bullhead, rainbow trout, and American eel. These three compounds influenced hepatic gluconeogenesis and glycogenolysis with significant species differences. Vasotocin and isotocin affected only eel hepatocytes activating gluconeogenesis by 1.7-fold and glycogenolysis by 3-fold. Phenylephrine increased glycogenolysis by 7-fold in bullhead hepatocytes and gluconeogenesis by 1.4-fold in trout cells. Vasotocin and phenylephrine actions were correlated with increases in adenosine 3',5'-cyclic monophosphate (cAMP). The vasotocin effects were unaffected by beta- and alpha-antagonists supporting a V2-type receptor on eel hepatocytes. Phenylephrine effects were abolished by propranolol and reduced by prazosin and yohimbine (alpha 1- and alpha 2-antagonists, respectively). Phenylephrine, therefore, affected fish hepatocyte metabolism either by a mixed alpha/beta-receptor mechanism emphasizing beta-adrenoceptors or the classic alpha/beta agonist/antagonist scheme defined for mammals is not appropriate for these fish preparations.