Baroreflex suppression of nonshivering thermogenesis in rats.

The effects of an elevation of arterial blood pressure (BP) on heat production (M) and interscapular brown adipose tissue temperature (Tbat) were studied at 15 degrees C in unanesthetized 5 degrees C-acclimated rats. The elevation in blood pressure (BP), caused by phenylephrine (PHE: 5-30 micrograms/(kg x min)) infusion for 10 min, decreased M and Tbat accompanied by a marked bradycardia. The decrease in M was not due to the suppression of shivering, because shivering did not appear under the present experimental conditions. After sinoaortic baroreceptor denervation, PHE infusion failed to produce these changes. After premedication with atropine, PHE infusion suppressed M and Tbat without the bradycardia. These results indicate that nonshivering thermogenesis (NST) in the brown adipose tissue (BAT) is suppressed by a sinoaortic baroreceptor reflex in response to an elevation of BP. Since metabolism of BAT is controlled by the sympathetic nervous system, the baroreflex inhibition of NST in the BAT may be largely attributed to the decrease of sympathetic nervous outflow to the BAT.