FURTHER EVIDENCE THAT BAT THERMOGENESIS MODULATES CARDIAC RATE IN INFANT RATS

Previous research in infant rats suggested that brown adipose tissue ( BAT), by providing warm blood to the heart during moderate cold exposu re, protects cardiac rate. This protective role for BAT thermogenesis was examined fur ther in the present study. In experiment 1, 1-wk-old rats in a warm environment were pretreated with saline or chlorisondam ine (a ganglionic blocker), and then BAT thermogenesis was stimulated by injection with the beta 3-agonist CL-316243. In experiment 2, pups were pretreated with chlorisondamine and injected with CL-316243, and after BAT thermogenesis was stimulated the interscapular region of the pups was cooled externally with a thermode. In both experiments, card iac rate, oxygen consumption, and physiological temperatures were moni tored. Activation of BAT thermogenesis substantially increased cardiac rate in saline- and chlorisondamine-treated pups, and focal cooling o f the interscapular region was sufficient to lower cardiac rate. The r esults of these studies support the hypothesis that BAT thermogenesis contributes directly to the modulation of cardiac rate.