Catecholamines and triiodothyronine variations and the calorigenic response to norepinephrine in cold-adapted and exercise-trained rats

Abstract

A comparison was made of the thermogenic response to norepinephrine (NE) in cold-adapted (2 h per day at -15.degree. C for 5 wk) and in exercise-trained rats (2 h swimming per day for 5 wk). The O2 consumption and the plasma catecholamine elevation were comparable for both conditions. Similarly plasma corticosterone determinations indicated comparable elevations in acute stress exposure and reduced responses in both exercise-trained and cold-adapted rats. The marked increase in colonic temperature which was observed in cold-adapted animals injected with NE (30 .mu.g/100 g s.c.) was not found in exercise-trained rats. Similarly the brown adipose tissue was double in size in the cold-adapted rats but remained unchanged with exercise training. An important elevation of triiodothyronin (T3) was found in cold-exposed rats, either adapted or not. Exerciose decreased plasma T3 in trained and nontrained rats. Swimming for 2 h and exposure to cold (-15.degree. C) for 2 h produced comparable elevation of plasma corticosterone and catecholamine, and of O2 consumption. Only the cold-adapted animals develop a NE-induced thermogenesis. Apparently thyroid hormones are necessary as permissive factor, in stress-induced thermogenesis.