LONG-TERM EFFECTS OF TRIIODOTHYRONINE AND THIOURACIL ON MYOCARDIAL β-ADRENERGIC RECEPTOR NUMBERS AND CYCLIC AMP CONCENTRATION IN RATS

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Long-term (35 days) effects of thyroid hormone on the number of myuocardial β-adrenergic receptors and the c-AMP concentration were studied in the rat. The ventricles from triiodothyronine-administered rats (T_3 rats) showed an increase in the number of β-receptors compared to controls (54.3±3.1 vs 39.3±1.8 fmole of [^<125>I]-iodohydroxybenzylpindolol (IHYP) binding sites/mg protein p<0.001) on the 35th day. Conversely, the ventricles from thiouracil-administered rats (TU rats) showed a decrease in the number of β-receptors compared to controls (31.4±1.6 vs. 38.4±2.6 fmole/mg protein, p<0.05). The equilibrium dissociation constants (Kd) for the interaction of receptors with IHYP did not differ significantly (0.10 to 0.15 nM). The myocardial concentration of cyclic AMP was not significantly different (T_3 rats, 1.09±0.09 nM/g wet weight tissue; T_3 controls, 1.12±0.07; TU rats, 1.13±0.07; TU controls, 1.16±0.12) on the 35th day. On serial effects of tri-iodothyronine from the first to the 35th day, the number of β-receptors of T_3 rates increased significantly on the 24th and the 35th day, but the c-AMP concentration was not significantly different from that in control rats. These results demonstrated that thyroid hormone affects the number of myocardial β-receptors in rats, and suggested a different mechanism of action of thyroid hormone on the myocardium from that of catecholamines.
社団法人日本循環器学会の論文
1984-05-20