Contribution of cyclic GMP generation to the relaxation by nipradilol in the rabbit aorta

1. Contribution of cyclic GMP generation to the relaxation by nipradilol of vascular smooth muscle was studied in the isolated rabbit aorta contracted by phenylephrine (10(-7) M) or prostaglandin F2 alpha (PGF2 alpha, 3 x 10(-6) M). 2. Nipradilol-induced relaxation in both contractions and increase in cyclic GMP content were inhibited by methylene blue (10(-5) M). 3. The relations between the increase in cyclic GMP and the relaxation produced by nipradilol and nitroglycerin were fitted to sigmoid curves. The increase in cyclic GMP at 50% relaxation by nipradilol was smaller than that by nitroglycerin (1.2-fold increase as against 3-fold increase). 4. These results suggest a smaller contribution of cyclic GMP generation through activation of soluble guanylate cyclase to nipradilol-induced relaxation in the rabbit aorta.