Acute thyroid hormone increases noradrenergic responsiveness of rat atria in vitro

The effect of acute (10-75 min) exposure of isolated spontaneously beating rat atria to L-triiodothyronine (T3)(12.9-1290 nM) on the positive chronotropic response to (-)-norepinephrine (NE) 10(-10)-10(-4)M) was examined. Preincubation (50 min) with 129 nM T3 increased the maximal response to (-)-NE from 128 +/- 10 to 176 +/- 11 beats/min. This effect was temporally biphasic, being maximal at 50 min pre-exposure. The results demonstrate an effect of acute in vitro exposure to T3 on the noradrenergic responsiveness of the heart.