Baroreflexive suppression of heat production and fall in body temperature following peripheral administration of vasopressin in rats.

Intravenous injection of vasopressin (lysin-8-vasopressin, LVP) in unanesthetized rats at an ambient temperature of 18 degrees C caused a decrease in heat production (M) followed by a fall in colonic temperature (Tco1). These changes were preceded by an elevation of aortic blood pressure (BP) and bradycardia, and were related to the dosage of LVP administered. Temperature of the interscapular brown adipose tissue (BAT) significantly fell after LVP injections. Therefore, it can be said that the decrease in metabolism by the peripheral LVP is at least partly due to suppression of BAT thermogenesis. After bilateral sino-aortic deafferentation, however, the changes in these variables were greatly but not completely reduced except for the elevation of BP. LVP of 0.25 micrograms, more than sufficient to cause a significant elevation of BP when administered peripherally, had no effect on M and Tco1 when injected into the anterior hypothalamus. From these results, we conclude that the hypothermic effect of vasopressin administered peripherally is largely attributed to the baroreflexive suppression of nonshivering thermogenesis, and is not due to the action on the temperature regulatory centers. The slight but insignificant suppression of metabolism in the sinoaortic denervated rats following injection of LVP may be caused by a decreased blood flow to the thermogenic tissues.