DIRECT EFFECTS OF THYROID-HORMONES ON RAT CORONARY-ARTERY - NONGENOMIC EFFECTS OF TRIIODOTHYRONINE AND THYROXINE

To determine whether thyroid hormones, triiodothyronine (T-3) and thyr oxine (T-4), have any direct, nongenomic effects on vascular smooth mu scle cells, we evaluated the effects of these hormones on rat coronary arteries. Bolus injection of T-3 or T-4 elicited a transient, dose-de pendent decrease in coronary perfusion pressure (CPP), as well as an i ncrease in arterial vasodilation. Vasodilation occurred immediately af ter injection, peaked at 15 seconds, and lasted 80 seconds. Reverse T- 3 had no effect on CPP or vasodilation. The rapidity of these effects suggests that they are not mediated by the T-3-nuclear receptor, but a re direct, nongenomic effects of thyroid hormones. Our results also su ggest that thyroid hormones may play a role in preventing myocardial i schemia by inducing coronary artery vasodilation.