Comparison of responses to sarafotoxins 6a and 6c in pulmonary and systemic vascular beds

Cardiovascular and pulmonary responses to sarafotoxin (S) 6a and S6c were investigated in the anesthetized cat. Intravenous injections of the peptides in doses of 0.1-1.0 nmol/kg caused decreases or biphasic changes in arterial pressure (AP) and increases in central venous pressure, pulmonary arterial pressure (PAP), and cardiac output (CO). Secondary decreases in CO were observed in response to higher doses, and biphasic changes in systemic (SVR) and pulmonary (PVR) vascular resistances were observed. Under constant-flow conditions, the peptides only increased pulmonary lobar arterial perfusion pressure and lobar vascular resistance. AP responses to S6a, S6c, endothelin (ET)-1, ET-2, vasoactive intestinal contractor (VIC), and Lys⁷-ET-1 were similar, whereas AP responses to S6b and ET-3 were similar. S6a, S6b, S6c, ET-1, ET-2, ET-3, VIC, Lys⁷-ET-1, and big ET-1 increased PAP. S6a and S6c increased distal aortic and superior mesenteric arterial (SMA) blood flow and caused biphasic changes at the highest doses. Under constant-flow conditions, S6a and S6c produced dose-dependent biphasic changes in hindquarters perfusion pressure. Changes in SVR and PVR in response to the peptide were not affected by hexamethonium, glyburide, or meclofenamate, indicating that responses are independent of autonomic reflexes, activation of ATP-regulated K⁺ channels, or release of cyclooxygenase products. In contrast, N-nitro-L- arginine methyl ester decreased hindquarters vasodilator response to S6a and S6c. The present data show that S6a and S6c produce both vasodilation and vasoconstriction in the systemic vascular bed and increase lobar vascular resistance and that hindquarters vasodilator responses are mediated, in part, by the release of endothelium-derived relaxing factor.