Difference In Relaxant Effects Research Articles

Inhibition of the action of nitric oxide prodrugs by pyocyanin: mechanistic studies

Previously, we reported on the antagonism by pyocyanin (PYO) of the relaxant effects of nitrovasodilators such as glyceryl trinitrate, S-nitroso-N-acetylpenicillamine (SNAP), and 3-morpholinosydnonimine (SIN-1). The purpose of the present study was to elucidate the mechanism of this action of PYO by examining its effect on the steps considered to be necessary for nitrovasodilator-induced relaxation of blood vessels. PYO (10 microM) attenuated the accumulation of guanosine-3',5'-cyclic monophosphate (cGMP) in rabbit aorta induced by nitrovasodilators SIN-1, SNAP, and GTN, 65, 81, and 67%, respectively. Additionally, PYO (1 or 10 microM) interfered with in vitro activation of soluble guanylyl cyclase. PYO did not inhibit vascular relaxation induced by 8-bromo-cyclic guanosine monophosphate. PYO (10 microM) also decreased the quantity of nitric oxide measured in the headspace above intact vascular tissue incubated with glyceryl trinitrate in the presence of oxygen. These observations are consistent with the interpretation that PYO interfered with the nitrovasodilator action of glyceryl trinitrate by inactivation of NO or by inhibition of enzymatic biotransformation of GTN; this would result in decreased guanylyl cyclase activation and thus lowering cellular levels of cGMP. NO chemiluminescence studies with SIN-1 (10 microM) revealed that this NO donor produced NO in a time-dependent manner and PYO (10 microM) caused no inhibition of NO production, but in fact, potentiated NO release after 10 min of incubation (1395 +/- 179 pmol NO compared with 1088 +/- 154 pmol NO). NO production from 10 microM SNAP was similarly potentiated by PYO after 0.5, 2, 5, and 10 min of incubation. Therefore, it is likely that PYO acts as an inhibitor of guanylyl cyclase with respect to NO donors, SIN-1 and SNAP, but it also appears that PYO can exert additional inhibitory effects in the case of vascular relaxation by GTN. Such differences in relaxant effects may reflect inhibition of enzymatic biotransformation that is unique to GTN or that PYO may complex with an alternative redox form of NO (perhaps NO+) that is generated by vascular metabolic activation of GTN.

Differences in relaxant effects of cyclic GMP on skinned muscle preparations from the proximal and distal colon of rats.

The relationship between the intracellular cyclic GMP content and relaxation of smooth muscle was studied in preparations from the proximal and distal colon of rats. Nitric oxide increased the cyclic GMP content of longitudinal muscle of both preparations to approximately the same extents. However, although nitric oxide at 0.03-10 microM induced concentration-dependent relaxation of the proximal segments, it did not induce any significant relaxation of the distal segments. The longitudinal muscle preparations were permeabilized by treatment with alpha-toxin to examine the relaxant effects of cyclic GMP on the contractile elements. Ca2+ induced contraction of the permeabilized muscle, the contraction consisting of a transient and subsequent tonic phases. Cyclic GMP (3-100 microM) reversed the tonic contractions induced by various Ca2+ concentrations (1-30 microM). The magnitude of the relaxant effect of cyclic GMP was significantly more in the proximal region than in the distal region. But in contrast to nitric oxide, cyclic GMP induced slight, but clear relaxation of the distal colon. The inhibitory effects of cyclic GMP on phasic contraction, like those on tonic contraction, were high in the proximal region and low in the distal region. These results suggest that the difference in the relaxant effects of nitric oxide in the proximal and distal longitudinal muscles is not due to a difference in extents of cyclic GMP generation, but mainly to a difference in the sensitivities of the contractile elements in the two regions to cyclic GMP.

Effects of Papaverine and Prostaglandin E(1), on Corpus cavernosum Smooth Muscle of Arteriogenically and Diabetically Impotent Men

Relaxant effect of prostaglandin E1 (PGE1) and papaverine (PAP) were measured in strips of corpus cavernosum smooth muscle taken from a healthy control group of men (A; n = 5), from arteriogenically impotent men (B; n = 6) and from additionally diabetic impotent men (C; n = 5) with venous leakage. Maximal relaxant effect was achieved with PAP at a mean of 10(-4) mol/l and PGE1 at a mean of 5.8 x 10(-6) mol/l. PAP induced complete relaxation in all strips. There was no difference in relaxant effects between groups. Relaxant effect was less pronounced and depended significantly on etiology: phenylephrine-induced tension was reduced by 76 +/- 8% (A), 54 +/- 14% (B) and 23 +/- 18% (C), respectively. In conclusion, our data suggest degradation of PGE1 receptors depending on the cause of erectile dysfunction. Furthermore, relaxant capacity of cavernous smooth muscle per se seems not to be impaired in impotence. Therefore, pathophysiology of venous leakage cannot sufficiently be explained by a lack of relaxation.