AJP - Regulatory, Integrative and Comparative Physiology, Vol 245, Issue 3 372-R378, Copyright © 1983 by American Physiological Society
Hyperinsulinemia in rats with hypothalamic obesity: effects of autonomic drugs and glucose
S. Inoue, Y. S. Mullen and G. A. Bray
The present study examined the effects of autonomic drugs and glucose on
the insulin and glucose concentrations of sham-operated rats and of rats
with ventromedial hypothalamic (VMH) lesions and obesity. In the basal
condition both epinephrine and atropine significantly decreased serum
insulin levels in VMH-lesioned but not sham-operated rats. During glucose
stimulation of insulin secretion in VMH-lesioned rats, epinephrine
inhibited the increase of insulin by 83% and atropine inhibited it by 42%;
whereas in sham-operated rats, epinephrine inhibited it by 70% and atropine
inhibited it by 34%. Epinephrine with atropine completely blocked the
increase of insulin in response to glucose in both VMH-lesioned and
sham-operated rats. In the basal condition, epinephrine together with
propranolol significantly decreased serum insulin levels in VMH-lesioned
but not sham-operated rats. Epinephrine with phentolamine, on the other
hand, markedly increased insulin in the VMH-lesioned rats and to a lesser
degree in the sham-operated rats. During glucose stimulation epinephrine
with propranolol inhibited the increase of insulin in both groups.
Epinephrine with phentolamine or isoproterenol markedly increased serum
insulin in VMH-lesioned rats. These results suggest that stimulation of the
vagus nerve and increased sensitivity of the beta-receptors on the
beta-cells of the islet contribute to the development of hyperinsulinemia.
The sympathetic contribution may also be through suppression of
alpha-adrenergic receptors.
