COMPARISON OF THE EFFECTS OF VARIOUS VASODILATORS ON THE RAT PORTAL-VEIN AND MESENTERIC-ARTERY

The effects of various vasodilators on isolated helical strips of rat portal vein and mesenteric artery were examined. Dilazep, ibudilast, n ifedipine, verapamil and papaverine relaxed the KCl- and norepinephrin e-induced contractions of the portal vein to a greater extent than the y relaxed those of mesenteric artery. Dibutyryl cyclic AMP and NKH477 did not show any significant difference in terms of the concentrations that produced 50% inhibition (IC50) of the KCl-induced contraction of the portal vein and mesenteric artery. The relaxant effects of nitrop russide and isosorbide dinitrate on the KCl- and norepinephrine-induce d contractions of the portal vein were less potent than their effects on contractions of the mesenteric artery. The agents that inhibited th e contractions of the portal vein more potently than those of the mese nteric artery were associated with parallel shifts to the right of the concentration-response curves for CaCl2 in both preparations. These r esults suggest that drugs with a Ca2+ channel blocking action may be p referable to those that cause a decrease in portal pressure for treatm ent of portal hypertension.