EFFECTS OF ENDOTHELIN ON CORONARY FLOW, MECHANICAL PERFORMANCE, OXYGEN-UPTAKE, AND FORMATION OF PURINES AND ON OUTFLOW OF PROSTACYCLIN IN THE ISOLATED RABBIT HEART

Endothelin is a 21-residue peptide formed during incubation of isolated porcine endothelial cells. Due to its pronounced vasoconstrictor activity, endothelin has been proposed to play a role in the regulation of vascular tone. We studied the effects of synthetic endothelin (0.1-10 nM) on coronary flow, mechanical performance, myocardial oxygen uptake, and formation of purines, and outflow of 6-ketoprostaglandin F(1α) (metabolite of prostacyclin) in rabbit hearts perfused with saline by the Langendorff method. Endothelin dose-dependently decreased the coronary flow, at 10 nM, by about 75%. Heart rate, ventricular contractility, myocardial oxygen uptake, and purine release were affected by endothelin no more than by a corresponding mechanical reduction of the coronary flow. In contrast, the diastolic relaxation appeared to be directly diminished by endothelin. The concentration of 6-ketoprostaglandin F(1α) in the cardiac effluent was dose-dependently elevated by about 14 times by endothelin (10 nM) (p < 0.001). A corresponding mechanical restriction of the coronary flow insignificantly affected the effluent concentration of 6-ketoprostaglandin F(1α). The calcium channel blocker nifedipine (1 μM) completely abolished the decrease in diastolic relaxation induced by endothelin and markedly counteracted the peptide-induced increase in effluent concentration of 6-ketoprostaglandin F(1α), but did not affect the vasoconstrictor activity. These data demonstrate that endothelin induces vasoconstriction and facilitates the outflow of prostacyclin in the rabbit heat. In addition, the peptide appears to affect diastolic relaxation in this organ.