The Effect of Adrenergic and Ganglionic Blockers upon the L-Dopa-Stimulated Release of Glucagon in the Rat

To help characterize the L-dopa-mediated release of glucagon, rats were given either L-dopa or dopamine (10 mg/kg) intravenously; portal plasma levels of insulin, glucagon and glucose were measured in the presence and absence of adrenergic and ganglionic blockers. The alpha-adrenergic blocker (phentolamine) suppressed the glucagon and glucose response to L-dopa and increased plasma insulin levels. Beta-adrenergic blockade with propranolol ameliorated the L-dopa-mediated glucagon and glucose responses but had no effect on plasma insulin levels. Ganglionic blockade with pentolinium tartrate was ineffective and did not alter any of the L-dopa-mediated responses of glucagon, insulin or glucose. These data indicate that L-dopa and dopamine probably act via the sympathetic nervous system through known pathways enchancing the release of glucagon. Furthermore they substantiate the fact that the adrenergic nervous system is involved in the regulation of the endocrine pancreas. (Author)