IMPAIRMENT OF COLD-INDUCED INCREASE IN THYROXINE 5'-DEIODINASE ACTIVITY IN MOUSE BROWN ADIPOSE-TISSUE BY THE INTRACEREBROVENTRICULAR ADMINISTRATION OF BOMBESIN

Effects of bombesin on brown adipose tissue (BAT) thyroxine (T4) 5'-de iodinase (5'D) activity and rectal temperature were examined in male m ice. Immediately following an intracerebroventricular (ICV) or intrave nous (IV) injection of bombesin (0.1-100 ng/animal) or vehicle (20 mM bacitracin dissolved in 0.9% saline), the mice were placed in a room a t 4-degrees-C or 22-degrees-C for 30, 60, 120 or 240 min. The ICV inje ction of bombesin dose-dependently lessened cold-induced increase in B AT 5'D activity and increased hypothermia determined at 120 min of col d exposure, whereas the IV injection of bombesin was without effect. B ombesin (ICV)-induced hypothermia preceded the inhibition of BAT 5'D a ctivity by at least 30 min at 4-degrees-C. BAT 5'D activity was not af fected by ICV injection of bombesin in mice kept at 22-degrees-C, alth ough the rectal temperature was significantly decreased. Bombesin thus appears to prevent cold-induced increase in T4 5'D activity in mouse BAT by its central effect. Bombesin-induced excessive hypothermia itse lf and/or the decrease in sympathetic tone of BAT by bombesin might de crease cold-induced increase in BAT 5'D activity.