Balance between endothelium-mediated dilating and direct constricting actions of serotonin on resistance vessels in the isolated rabbit heart.

To determine whether endothelium-derived relaxing factor (EDRF) contributes to the vasomotor action of serotonin (5-HT) in the coronary resistance bed, we used haemoglobin as an inhibitor of EDRF in isolated perfused rabbit hearts. The 5-HT-induced dilatation (14 +/- 2% change in vascular resistance) was converted to constriction (10 +/- 3% change) in the presence of haemoglobin, while the vasodilator responses to papaverine were not attenuated. This is consistent with a role for EDRF in the mediation of 5-HT-induced coronary resistance vessel dilatation.