AJP - Regulatory, Integrative and Comparative Physiology, Vol 252, Issue 4 653-R660, Copyright © 1987 by American Physiological Society

ARTICLES

Hormonal regulation of hepatic glycogenolysis in the carp, Cyprinus carpio

P. A. Janssens and P. Lowrey

Carp (Cyprinus carpio) liver maintained normal glycogen content and enzyme complement for several days in organ culture. Epinephrine-stimulated glycogenolysis, phosphorylase activation, and cyclic AMP (cAMP) accumulation in a concentration-dependent manner with EC50s of 100, 100, and 500 nM, respectively. These actions were blocked by the beta-adrenergic antagonist, propranolol, but not by the alpha-adrenergic antagonist phentolamine. Glycogenolysis and tissue cAMP were uninfluenced by 10(-6) M arginine vasotocin, arginine vasopressin, lysine vasotocin, lysine vasopressin, mesotocin, or oxytocin, but were slightly increased by 10(-5) M isotocin and slightly decreased by 10(-6) M angiotensin II. [125I]-iodocyanopindolol (ICP), a beta-adrenergic ligand, bound to isolated carp liver membranes with a KD of 83 pM. Maximum binding of 45 fmol/mg protein was at 600 pM. Propranolol, isoprenaline, epinephrine, phenylephrine, norepinephrine, and phenoxybenzamine displaced ICP with KDs of 100 nM, 2, 20, 20, 60, and 200 microM, respectively. The alpha-adrenergic antagonists, yohimbine and prazosin, showed no specific binding. These data provide evidence that catecholamines act via beta-adrenergic receptors in carp liver and that alpha-adrenergic receptors are not present. Vasoactive peptides play no significant role in regulation of carp liver glycogenolysis.

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