Physiological Activity of the Brown Adipose Tissue

摘要

Brown adipose tissue was recently found to be a major site of heat production in cold-adapted animals. It is also known that the increased secretion of thyroid hormone is responsible for the thermogenesis during cold exposure. Accordingly, the thyroid hormone is possibly presumed to stimulate the metabolic activity of brown adipose tissue. The present study was mostly attempted to know the functional relationship between thyroid hormone and brown adipose tissue with respect to cold exposure. In the first series of experiments oxygen consumption of interscapular brown adipose tissue of the mouse was determined. Cold exposure for 5 days produced a significant increase in fat-free dry matter of brown adipose tissue. Concurrent rise in oxygen consumption of this tissue was found. In the next series of experiments, blood flow through interscapular brown adipose tissue was estimated by radioactive indicator method under various experimental conditions in the rat. Chronic cold exposure at 4-5C for 2 weeks as well as acute exposure at 3C for 30 min resulted in a marked increase in the blood flow, 14.7-fold and 2.5-fold respectively. Intravenous infusion of norepinephrine into normal rats produced 6.4-fold increase in the blood flow through brown adipose tissue. Thyroidectomized and methylthiouracil-treated rats failed to respond to chronic cold exposure in increasing the blood flow through brown adipose tissue. (Author)