Effects of smooth muscle relaxants on KCl- and histamine-induced contractile responses in isolated rabbit basilar artery, aorta and taenia coli

Abstract

Effects of D 600(D), diltiazem(Dil), Aspaminol(Asp), papaverine(Pap) and sodium nitroprusside(NP) were studied KCl-induced contraction: D, Dil, Asp and Pap reduced the maximal responses of the concentration-response curves in all of the tissues in normal medium (Ca,2.5mM). The reductions by Asp in aorta and by D, Dil, Asp and Pap in taenia coli were significantly reversed by increasing external Ca concentrations (Ca,12.5mM). NP little affected the contractile response in taenia coli. The reductions by NP were not affected by increasing external Ca concentrations in basilar artery and aorta Histamine-induced contraction: Maximal responses in basilar artery and taenia coli were reduced by D, Dil, Asp and Pap but not by NP, and that in aorta was reduced by Pap and NP. The reductions by NP in aorta and by Asp and Dil in taenia coli were reversed by increasing external Ca concentrations. The results of the experiments using Ca-free medium suggested that the inhibition of histamine-induced release of intracellularly sequestered Ca by D, Asp and Pap might at least contribute to the inhibitory effects of these relaxants in normal medium in basilar artery and aorta, whereas these might be mainly due to the inhibition of influx of extracellular Ca in taenia coli. Dil, only in taenia coli, and NP, only at higher concentration; in all of the tissues were also considered to inhibit the release of intracellular ly sequestered Ca. Thus, it is possible that the actions of smooth muscle relaxants vary with the difference in cellular Ca movements due to the tissue types and the conditions during development of contractions, including contractile agents and any other factors.