Histochemical fluorescence studies on noradrenaline accumulation by Uptake 2 in the isolated rat heart.

1. The distribution of noradrenaline accumulated by Uptake(2) (Iversen, 1965) in the isolated perfused rat heart has been observed using histochemical fluorescence microscopy.2. On the basis of the technique used, noradrenaline seems to be predominantly associated with the cardiac muscle cells, but sympathetic nerves and other cardiac structures also serve as retention sites.3. Phenoxybenzamine, normetanephrine and perfusion with noradrenaline at 20 degrees C all decreased noradrenaline accumulation.4. Lowered temperature significantly increased the perfusion pressure and significantly decreased the [(14)C]-sorbitol space in perfused hearts.5. The implications of these results are discussed.