Sympathetic activity following paraventricular injections of glucose and insulin.

The effect of microinjections of glucose and insulin into the paraventricular nucleus (PVN) on sympathetic firing rate has been examined in rats. Following the injection of insulin 144 pmoles, there was a 30% reduction in sympathetic firing rate with a minimum reached 2 minutes following the injection, and recovery to baseline within 4 minutes. Lower doses of insulin were without effect. Following the injection of glucose 138 nmoles, there was a brief 20% increase in sympathetic firing rate which peaked at 1 minute and had returned to control levels by the second minute. This effect of glucose, like that of insulin, was dose-related. When compared with injections of insulin and glucose into the ventromedial hypothalamus, injection of either substance into the PVN showed a smaller and more attenuated response, raising the possibility that the effect of these nutrients injected into the PVN may be through the small quantities which could reach the ventromedial nucleus. These studies are consistent with the hypothesis that the paraventricular nucleus is not the principal modulator of the sympathetic firing rate.