Experiments were designed to verify whether or not acute or chronic exposure to dexfenfluramine favors the occurrence of coronary vasospasm in vivo or in vitro. Rings of left anterior and left circumflex porcine coronary artery, with and without endothelium, were studied in conventional organ chambers for the measurement of isometric force. The donor pigs were divided into two groups: controls and animals fed for 4 weeks with dexfenfluramine. In each group, one-half of the animals underwent balloon denudation of the left anterior descending coronary artery at the beginning of the study. Coronary angiography was performed at the time of denudation and, in all animals, during the 3rd week of the study. Acutely, dexfenfluramine at concentrations higher than 10(-5) M caused contractions which were blunted by the presence of the endothelium and inhibited by indomethacin (an inhibitor of cyclooxygenase). Chronic treatment with dexfenfluramine did not affect coronary diameter and did not alter the response to intracoronary infusion of serotonin. Chronic treatment with dexfenfluramine reduced the contractions of rings without endothelium to serotonin, but not those to norepinephrine or endothelin. It did not affect endothelium-dependent relaxations in the absence or presence of pertussis toxin to serotonin, UK14304 (alpha-2 adrenergic agonist), adenosine diphosphate or aggregating platelets. Chronic treatment with dexfenfluramine did not modify relaxations of rings without endothelium to SIN-1 (nitric oxide donor; the active metabolite of molsidomine) or adenosine diphosphate. These findings do not support the hypothesis that acute or chronic exposure to dexfenfluramine favors the occurrence of coronary vasospasm.