Catecholamine effect on cyclic adenosine 3':5'-monophosphate level in isolated catfish hepatocytes

The effect of catecholamines (epinephrine, norepinephrine, isoproterenol, and phenylephrine) on cyclic adenosine 3':5'-monophosphate (cAMP) level in isolated catfish (Ictalurus melas) liver cells was studied in the presence or absence of alpha (phentolamine) and beta (propranolol)-receptor antagonists. All catecholamines increased the hepatocyte cAMP level: the rank of their potency was epinephrine = isoproterenol greater than norepinephrine greater than phenylephrine. Propranolol completely blocked the catecholamine effect; phentolamine was ineffective. Results confirm previous findings (L. Brighenti, A. C. Puviani, M. E. Gavioli, and C. Ottolenghi, 1987, Gen. Comp. Endocrinol. 66, 306-313) that epinephrine and norepinephrine act via beta-receptor activation. However, the comparison of the effects of isoproterenol and phenylephrine on cAMP with those on phosphorylase alpha and on glycogen breakdown suggests that a more complex mechanism is possibly involved in the catecholamine effect on catfish glycogenolysis.