Influence of cAMP and calcium on epinephrine-mediated hepatic glycogenolysis in rainbow trout, Oncorhynchus mykiss

Abstract

1. The role of cAMP and of calcium in mediating epinephrine-stimulated glycogenolysis was studied by incubating rainbow trout liver in vitro. 2. Epinephrine significantly stimulates glucose release from liver pieces incubated in either calciumcontaining or calcium-free medium. However, the development of the glycogenolytic profile occurred more rapidly in the presence of calcium. 3. The β-antagonist, propranolol, inhibited epinephrine-stimulated glucose release from liver pieces incubated in either calcium-containing or calcium-free medium. 4. Calcium ionophore, A3187, stimulated glucose release from liver pieces incubated in calciumcontaining medium. Verapamil, a putative calcium channel blocker, had no effect on A23187-stimulated glycogenolysis. However, verapamil completely inhibited epinephrine-stimulated glycogenolysis. 5. Dibutyryl cAMP and IBMX, singly or together, stimulated glucose release from liver pieces. cAMP-mediated glycogenolysis was more pronounced in liver pieces incubated in calcium-containing medium. 6. These results indicate that epinephrine-stimulated hepatic glycogenolysis in rainbow trout proceeds through the activation of β-adrenergic receptors and that both cAMP and calcium are involved in the post-receptor signal transduction process.