Glucagon Release after Stimulation of the Lateral Hypothalamic Area in Rats: Predominant β-Adrenergic Transmission and Involvement of Endorphin Pathways*

Catheterization of the portal vein and stereotaxic implantation of electrodes in the lateral hypothalamic area (LHA) were performed in normal rats after thiopental anesthesia. Immunoreactive glucagon (IRG) and insulin (IRI), glucose, catecholamines, and β-endorphin were monitored in portal and peripheral plasma, before and during electrical stimulation of the LHA. The influences on glucose and hormone concentrations of propranolol, phentolamine, atropine, and naloxone infusions were also investigated in similar rats. A basal portoperipheral concentration gradient was found for IRG, IRI, and catecholamines, but not for β-endorphin. The LHA stimulation induced a significant rise in portal catecholamine, IRG, and glucose concentrations; IRI remained unchanged; the portoperipheral catecholamine gradient was augmented. These alterations were not observed after bilateral splanchnicectomy. Propranolol infusion abolished the LHA-dependent IRG and glucose rises. Naloxone reduced the IRG rise significantly. Phentol...