Effects of a K⁺(ATP) channel opener, lemakalim, on systemic, coronary and regional vascular dynamics in conscious dogs: Comparison with nifedipine, adenosine, nitroglycerin and acetylcholine

The systemic, coronary and regional vascular responses to the K⁺(ATP) channel opener lemakalim were compared to other potent vasodilators (i.e., nifedipine, adenosine, nitroglycerin and acetylcholine). Experiments were performed in 12 conscious dogs 2 to 4 weeks after implantation of aortic catheters and flow probes on the ascending aorta, left circumflex coronary, celiac, mesenteric, renal and iliac arteries, and solid-state miniature pressure gauges in the left ventricular cavity. Dose-response curves induced by bolus injection (i.v.) were examined. For doses that reduced total peripheral resistance by 22%, lemakalim reduced celiac (-28 ± 2%), mesenteric (-24 ± 3%), renal (-17 ± 3%) and iliac (-18 ± 3%) vascular resistances (i.e., by amounts similar to those observed with the other vasodilators, except for adenosine, which increased renal resistance). At these doses, lemakalim induced a greater decrease (-52 ± 3%) (P < .05) in coronary resistance, as compared with nifedipine (-35 ± 3%), adenosine (-38 ± 3%), nitroglycerin (-25 ± 2%) and acetylcholine (-32 ± 3%). However, when near maximal vasodilation was elicited, adenosine elicited the greatest (P < .05) decrease in coronary resistance (-81 ± 1%), as compared with lemakalim (-74 ± 2%), nifedipine (-67 ± 2%), nitroglycerin (-63 ± 2%) and acetylcholine (-72 ± 1%). Both the time to maximal increases in regional blood flow and the time for recovery in all vascular beds were significantly prolonged for lemakalim compared with the other vasodilators. Thus, the K⁺(ATP) channel opener lemakalim dilates the coronary bed out of proportion to other vascular beds, is relatively more potent at lower doses than other vasodilators and exhibits a delayed and more prolonged action in all regional vascular beds.