The Role of Adrenergic Agonists on Glycogenolysis in Rat Hepatocyte Cultures and Possible Involvement of NO

Summary Certain liver metabolic diseases point to the presence of disturbances in glycogen deposition. Epinephrine raises the cAMP level that activates protein kinase A leading to the activation of phosphorylase and glycogen breakdown. In the present report, we sought to investigate whether NO is produced during adrenoceptor agonist-induced glycogenolysis in rat hepatocytes in cultures. Isolated glycogen rich rat hepatocytes in cultures were used. NO production (NO2 - ) was assessed under the effect of adrenergic agonists and adrenergic agonist/antagonist pairs, dibutyryl cyclic AMP sodiumpotassium salt (db-cAMP), NO synthase (NOS) inhibitors N ω -nitro-L-arginine methyl ester (L-NAME), aminoguanidine (AG) and the NO donor S-nitroso-N-acetyl penicillamine (SNAP). The inducible NO synthase (iNOS) mRNA was examined by the reverse transcription-polymerase chain reaction (RT-PCR). Glycogenolysis was quantified by glucose levels released into medium. The amount of glucose and NO2 - released by hepatocytes was increased as a result of epinephrine, phenylephrine or db-cAMP treatments. The increase in glucose and NO2 - released by epinephrine or phenylephrine was blocked or reduced by prazosin pretreatment and by NOS inhibitors aminoguanidine and LNAME. iNOS gene expression was up-regulated by epinephrine. It can be concluded that glycogenolysis occurs through α-adrenoceptor stimulation and a signaling cascade may involve NO production.