Effects of thyroid hormone replacement on P-adrenergic responsiveness of food-deprived rats

iol. 250 (Regulatory Integrative Comp. Physiol. 19): Ml-RB67,1986.-Thyroid hormone levels and p-adrenergic respon-siveness after stimulation with the /3-adrenergic agonist isopro-terenol were studied in four groups of male rats. The groups used were control rats, rats deprived of food for 72 h, rats administered 50 pg thyroxine (T,)/kg daily for 4 days, and rats deprived of food for 72 h and administered 50 pg TJkg daily for 4 days. Food deprivation significantly decreased serum Tq and triiodothyronine (Ts) levels, and administration of Tq significantly increased serum Tq and T3 levels in both fed and food-deprived rats. Administration of T4 led to lower body weights in both fed and food-deprived rats. Administration of isoproterenol led to increases in colonic and tail skin tempera-tures and heart rate. Food deprivation significantly attenuated the increased body temperatures and heart rate induced by isoproterenol, and administration of T4 to food-deprived rats returned these adrenergic responses to control levels. Admin-istration of Tr to fed rats significantly increased the thermal and cardiac responses to isoproterenol above those of the con-trol rats. Administration of isoproterenol also increased plasma glucose levels. Food deprivation significantly decreased both postsaline- and isoproterenol-stimulated glucose levels. How-ever, administration of T4 was without effect on either the postsaline- or isoproterenol-stimulated glucose levels of either the fed or food-deprived rats. The decreases in Ta and Ta that accompany food deprivation may thus be responsible for some, but not all, of the reductions i