INHIBITION OF THE EARLY CIRCULATORY EFFECTS OF TRIIODOTHYRONINE IN RATS BY PROPRANOLOL

  • 1 January 1981
    • journal article
    • research article
    • Vol. 30  (4) , 347-351
Abstract
In 2 identical experiments, A and B, the effect of the simultaneous i.v. injection of propranolol (Inderal, 0.5 mg/kg) on the circulatory effects of triiodothyronine (T3 500 .mu.g/kg i.v. 3 h before measuring) was studied. The 2 substances act at different rates; the blocking effect of propranolol preceded the development of the circulatory effects of T3. Cardiac output was measured by the Evans blue dilution method, the heart rate was calculated from the ECG recording and blood pressure was measured with a mercury manometer; stroke volume and total peripheral vascular resistance were also calculated. The isolated injection of T3 was followed by a significant increase in cardiac output (experiment A: 129%, B: 118%) and stroke volume (A: 125%, B: 118%) and by a drop in total peripheral vascular resistance (A: 82%, B: 85%). There was no change, in this early phase, in the heart rate or blood pressure. No changes were found 3 h after the isolated administration of Inderal (the maximum effect of propranolol is attained in 30-60 min). During the same period these initial effects of T3 were completely suppressed by the simultaneous injection of Inderal. These results were probably related to the experimental conditions (early and not very marked changes after T3), but they demonstrate that the initial effects of T3 on cardiac performance and on the peripheral blood vessels can be completely suppressed by a block of .beta.-receptors. .beta.-Adrenergic regulation apparently is an important part of the mechanism of the early hemodynamic action of T3.