AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 5 861-R867, Copyright © 1986 by American Physiological Society
Effects of thyroid hormone replacement on beta-adrenergic responsiveness of food-deprived rats
C. C. Barney, K. E. Wuertz and M. J. Katovich
Thyroid hormone levels and beta-adrenergic responsiveness after stimulation
with the beta-adrenergic agonist isoproterenol were studied in four groups
of male rats. The groups used were control rats, rats deprived of food for
72 h, rats administered 50 micrograms thyroxine (T4)/kg daily for 4 days,
and rats deprived of food for 72 h and administered 50 micrograms T4/kg
daily for 4 days. Food deprivation significantly decreased serum T4 and
triiodothyronine (T3) levels, and administration of T4 significantly
increased serum T4 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 temperatures 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. Administration of T4
to fed rats significantly increased the thermal and cardiac responses to
isoproterenol above those of the control rats. Administration of
isoproterenol also increased plasma glucose levels. Food deprivation
significantly decreased both postsaline- and isoproterenol-stimulated
glucose levels. However, 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 T4 and T3 that accompany food
deprivation may thus be responsible for some, but not all, of the
reductions in beta-adrenergic responsiveness observed in food-deprived
rats.
