Brown adipose tissue heat production in heat acclimated and perchlorate treated rats

The noradrenaline-induced energy dissipation rate was measured with a direct microcalorimeter in brown adipose tissue taken from rats acclimated to 34 degrees C (HA), perchlorate treated (PC) and heat acclimated-perchlorate treated (HAPC). The response to 10(-7) M NA was reduced by 45%, 47% and 86% in HA, PC and HAPC groups, respectively, as compared to a control group kept at 24 degrees C. In the same groups, the response to 10(-6) M NA was reduced by 34%, 7% and 64%, respectively. The specific activity of the soluble alpha-glycerophosphate dehydrogenase in brown fat from HA rats was reduced by 50%, whereas it was not altered in the PC animals. It is concluded that the sensitivity to noradrenaline of the brown adipose tissue thermogenic mechanisms is decreased in hypothyroidism, and that the acclimation temperature and the thyroid status per se each have a different influence on brown adipose tissue function.