Effects of nipradilol on the microvascular tone of rat mesentery: comparison with other beta-blockers and vasodilators.

The effects of nipradilol, a nonselective beta-blocker with vasodilator activities, on the diameter of arterioles and venules were examined in rat mesentery in vivo and were compared with those of propranolol, atenolol, labetalol, nifedipine and nitroglycerin. Topical application of nipradilol (10(-7) M and 10(-6) M) dilated the arterioles significantly to 109 +/- 2% and 112 +/- 2% of control, respectively (mean +/- S.E.; n = 9; p < 0.01), without changes in blood pressure and pulse rate. The dilator effect was comparable to that of nifedipine and nitroglycerin. Propranolol constricted the arterioles (to 86 +/- 3% at 10(-7) M; n = 9; p < 0.01), but atenolol and labetalol had no significant effects. Nitroglycerin dilated venules significantly (to 108 +/- 2% at 10(-7) M; n = 6; p < 0.01) but other drugs showed no significant effects on the tone of venules. Unlike the other beta-blockers used in this study, nipradilol has dilator effects on arterioles as have nifedipine and nitroglycerin.