Triiodothyronine acutely increases blood flow in the ventricles and kidneys of anesthesized rabbits.

Thyroid hormone (triiodothyronine [T(3)]) has various nongenomic effects, including alterations in glucose and fatty acid metabolism, augmentation of intracellular Ca(2+), enhancement of myocardial contractility, and vascular dilatation. However, its effect on regional blood flow remains to be established. We have measured the effect of T(3) on blood flow in major organs of anesthetized rabbits in vivo using the microsphere method. Under artificial respiration, nonradioactive microspheres (5 x 10(5)) labeled with barium were injected to measure blood flow at control level. Then, T(3) (50 microg/kg per milliliter) was administered and microspheres labeled with iodine (5 x 10(5)) were injected. The atria, ventricles, kidneys, and right upper limb were excised and their contents of microspheres were evaluated. Blood flow in the ventricles was significantly increased by T(3) (2.9 +/- 0.3 versus 3.4 +/- 0.3 mL/min per gram, vehicle versus T(3)). Similarly, blood flow in the kidneys was significantly higher after T(3) injection (4.3 +/- 0.5 versus 5.1 +/- 0.5 mL/min per, vehicle versus T(3)). The blood flow in the atria and skeletal muscles remained unchanged. These results indicate that the vasodilatory response to T(3) is not uniform and occurs preferentially in major organs such as cardiac ventricles and kidneys; this may be relevant to the T(3)-induced improvement of cardiac function.