A comparison of the relaxant effects of pinacidil in guinea-pig trachea, aorta and pulmonary artery.

The relaxant activity of pinacidil, a proposed K+ channel opener, was compared in isolated guinea-pig trachea, aorta and pulmonary artery. In preparations precontracted by histamine or PGF2 alpha, pinacidil produced complete tracheal relaxation but only partial relaxation of vascular tissues. The order of responsiveness was: pulmonary artery greater than trachea greater than aorta. The slope of the pinacidil concentration-effect (C/E) curve was much steeper in the tracheal than in the vascular preparations. The pinacidil C/E curves for relaxation were similar when the three types of preparations were precontracted by 124 mM K+. Pretreatment with pinacidil caused a parallel shift of the tracheal histamine C/E curve to the right, whereas the maximal response to histamine was markedly depressed in the pulmonary artery.