alpha-adrenoceptor-mediated glucose release from perifused catfish hepatocytes

In fish liver catecholamines bind to beta-adrenoceptors (AR) and increase g lucose release via cAMP augmentation. alpha(1)-AR have recently been shown to mediate IP3 and Ca2+ elevation in catfish and eel hepatocytes, although their coupling to a physiological response has remained doubtful. We have p erifused isolated catfish hepatocytes in Bio-Gel P4 columns with epinephrin e in the presence of prazosin and/or propranolol, alpha- and beta-AR antago nists, respectively. Ten nM epinephrine stimulated glucose release approxim ately 3-fold, and this effect was completely antagonized by the simultaneou s presence of both alpha- and beta-AR blockers. The two AR antagonists sepa rately inhibited about one-third and two-third of the total stimulation, re spectively. Through alpha-AR occupancy, epinephrine provoked a significant increase of glucose release whereas no stimulation was detected in Ca2+-dep leted hepatocytes. Glucose release was strongly elevated by both ionomycin and dibutyryl cAMP. These results represent the first direct evidence that alpha-AR transduction pathway is involved in epinephrine-induced glucose re lease from fish hepatocytes.