AJP - Endocrinology and Metabolism, Vol 256, Issue 4 E459-E466, Copyright © 1989 by American Physiological Society
Food intake, body and heart composition, and heart rate in T3 plus atenolol-treated rats
U. Burgi, M. E. Burgi-Saville, F. Ziegler, L. Krahenbuhl, G. Huber and C. Schoch
University Clinic of Medicine, Inselspital, Bern, Switzerland.
Thyroid hormones and beta-blockers both affect energy balance and the
heart. The interaction of 3,5,3'-triiodothyronine (T3) and the beta-blocker
atenolol on some cardiac and energy balance parameters was therefore
investigated. Stock-fed male Wistar rats (approximately 400 g) received 5
micrograms (expt 1) or 1.5 micrograms (expt 2) T3.100 g body wt-1.day-1 for
3 wk, with or without atenolol. In expt 3, rats were overfed with a
"cafeteria" diet before and during the experiment and otherwise treated as
in experiment 2. Compared with stock-fed (expt 1 and 2) or overfed (expt 3)
controls, T3 caused an increase in food intake in experiments 1 and 2 but
not in experiment 3. There was a large loss of body fat in all experiments,
disproportionately greater than the body weight loss. Protein loss was
significant only in experiment 1 and negligible in cafeteria rats. Heart
rate and weight were increased, although heart composition remained
unchanged. Atenolol, in a dose that abolished T3-induced tachycardia, did
not modify any of the other T3 effects investigated, including the
hypertrophy of the heart. These results indicate that T3-induced
tachycardia can be abolished by concomitant treatment with a beta-blocker
without altering parameters connected with energy balance, whereas protein
loss caused by T3 can be attenuated by lowering the dose of T3 used and can
be further blunted by dietary manipulation (cafeteria overfeeding).
