Oral induction of the insulin hyper-responsiveness in rats with ventromedial hypothalamic lesions

Bilateral electrolytic or sham-lesions of the ventromedial nuclei of the hypothalamus (VMH) were performed on fasting (prior to and after the lesion) ether anesthetized rats. Post-operatively (2 hours), sham-operated rats were either offered an oral glucose solution or were submitted to an intravenous glucose injection or were left undisturbed; lesioned rats were offered an oral glucose load or were submitted to an intravenous glucose injection. Three hours later, the insulin response to an intravenous glucose load was tested in all rats. No significant difference could be detected between the results obtained in the three subgroups of sham-operated rats. By contrast, the VMH lesioned rats exhibited a differential response according to the post-lesion treatment. In lesioned rats, given an intravenous glucose injection in the immediate post-lesion period, the tested insulin response was not significantly different from the response of the controls. When lesioned animals were allowed to taste and ingest as little at 0.5 g glucose, the tested insulin response was greatly enhanced. It is concluded that an oral intake is a prerequisite to the induction of the insulin hyper-responsiveness characteristic of fed VMH lesioned rats and that a 0.5 glucose oral intake is sufficient.