AJP - Regulatory, Integrative and Comparative Physiology, Vol 254, Issue 1 33-R39, Copyright © 1988 by American Physiological Society
Thyroxine, renal beta-adrenergic receptors, and dipsogenesis in food-deprived rats
L. F. Yeh, S. P. Baker and M. J. Katovich
Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville 32610.
The effect of thyroxine (T4) replacement on the increased renal
beta-adrenergic receptor number and the increased beta-adrenergic
dipsogenic responsiveness of fasted rats was studied in male Sprague-Dawley
rats. Food deprivation significantly decreased serum thyroxine (T4) and
triiodothyronine (T3) levels, increased the dipsogenic response to
isoproterenol, and elevated renal beta-adrenergic receptor concentration.
Daily administration of T4 (40 micrograms/kg) to food-deprived rats
restored serum thyroid levels to normal. Thyroxine replacement also reduced
the increased beta-adrenergic dipsogenic responsiveness in the
food-deprived rats to control levels. In addition, daily administration of
thyroxine reduced the beta-adrenergic receptor concentration in renal
cortices to that observed in controls. Thyroid treatment tended to decrease
the isoproterenol-induced renin release in food-deprived rats and increase
the response in the control rats. These results suggest that the relative
hypothyroid state observed in the food-deprived rat may be responsible for
the increased concentration of renal beta-receptors and the associated
activation of the renin-angiotensin system, which may be partially
responsible for the observed increased dipsogenic response induced by
isoproterenol. Collectively, the data reaffirm the interaction of thyroid
hormone and beta-adrenergic responsiveness, although it is of interest
that, in regard to renal beta-receptors, the concentrations are decreased
to normal by thyroid treatment, whereas previous studies in hypothyroid
rats demonstrate an increase to normal of cardiac beta-receptors. This
would suggest thyroid hormone may normalize a response in an opposite
direction depending on the direction of the disturbance.
