VMH Procainization abolishes cephalic phase insulin response

Abstract

In order to test the cephalic phase hypothesis of the ventromedial hypothalamus (VMH) obesity syndrome [22], the saccharin-induced cephalic phase insulin response was quantified with and without prior microinjections of procaine-HCl into the VMH of freely moving rats. Saline control injections into the VMH did not change the cephalic phase insulin response observed after the ingestion of 2 ml of 0.15% Na-saccharin. The low dose of procaine HCl (2×15 μg) attenuated, and the larger dose (2×50 μg) completely abolished this insulin response. The possibility that the early insulin response and its suppression could be the consequences of an unspecific oral sensation, general arousal or motor behavior were ruled out by the observations that oral quinine stimulation did not produce a comparable insulin response, and that glucose-stimulated insulin secretion in anesthetized rats was also attenuated by VMH procainization. The results are discussed in the light of the apparent dissociation between the behavioral and endocrine effects of VMH procainization as compared to electrolytic lesions and electrical stimulation of the VMH.