Effect of Vagotomy on Serum Insulin in Rats with Paraventricular or Ventromedial Hypothalamic Lesions*

Abstract

The effects of vagotomy on plasma glucose and insulin levels in rats with paraventricular nuclear (PVN) or ventromedial hypothalamic (VMH) lesions were measured during a constant glucose infusion. In one experiment, vagotomy was performed 50 min after the lesions, and in a second experiment, it was performed at the same time as the lesions. After the introduction of lesions in the PVN, there was a significantly greater rise in plasma glucose than in animals with either large or small VMH lesions, both of which had plasma glucose values similar to those in the sham-lesioned animals. The rise in insulin was greater in all three lesion groups than in the sham-operated animals. Although both plasma glucose and insulin had begun to decline before the vagotomy performed 50 min after lesioning, there was a further subsequent fall after vagotomy which was greater in the VMH-lesioned animals with large lesions than in rats with PVN lesions or small VMH lesions. In the sham-lesioned rats, there was no significant change in insulin or glucose after vagotomy. When the vagotomy and hypothalamic lesions were performed simultaneously, the glucose and insulin values in all groups were the same. The present experiments suggest that VMH and PVN exert different controls over pancreatic hormone secretion. The VMH lesions appear to remove an inhibitory effect on the vagus, with resultant hyperinsulinemia in the absence of hyperglycemia. The PVN-lesioned animals show a hyperglycemia which is abolished by vagotomy, suggesting that the PVN connects to vagal fibers which activate the glucagon secretory system in the alpha-cell of the pancreas.

Injection of Urocortin 3 into the ventromedial hypothalamus modulates feeding, blood glucose levels, and hypothalamic POMC gene expression but not the HPA axis

“…Acute electrical or chemical stimulation of VMH neurons in most cases did not significantly modify plasma levels of insulin (8,48,50). On the other hand, VMH lesion leads to chronic hyperinsulinemia (44,45,54), and vagotomy attenuates the elevation of insulin levels. These studies suggest that VMH neurons do not acutely modulate insulin secretion, but, under chronic conditions, the VMH plays a profound modulatory role in plasma insulin levels through regulation of parasympathetic outflow.…”

Studies of different female rat models of hypothalamic obesity

“…VMN-lesioned rats also showed lower activity levels and disturbed circadian rhythms (25,50) . Hyperphagia and obesity observed in VMN-lesioned rats are possibly a result of a disturbed balance between NPY and POMC signaling neurons, as well as between orexigenic and anorexigenic secondary neurons.…”

Pediatric Endocrine Disorders of Energy Balance

“…VMH lesions damage this pathway, leading to an increase in vagal firing rate [82]. For example, rats with VMH lesions exhibit both increased insulin levels and food intake; however, this can be prevented by pancreatic vagotomy [83][84][85]. Overactive vagal neurotransmission increases insulin secretion from β-cells through three distinct but overlapping mechanisms [86] (Fig.…”