Modulation of PGF sub(2 alpha )- and hypoxia-induced contraction of rat intrapulmonary artery by p38 MAPK inhibition: a nitric oxide-dependent mechanism

The mechanisms through which p38 mitogen-activated protein kinase (p38 MAPK) is involved in smooth muscle contraction remain largely unresolved. We examined the role of p38 MAPK in prostaglandin F sub(2 alpha ) (PGF sub(2 alpha ))-induced vasoconstriction and in hypoxic pulmonary vasoconstriction (HPV) of rat small intrapulmonary arteries (IPA). The p38 MAPK inhibitors SB-203580 and SB-202190 strongly inhibited PGF sub(2 alpha )-induced vasoconstriction, with IC sub(50)s of 1.6 and 1.2 mu M, whereas the inactive analog SB-202474 was similar to 30-fold less potent. Both transient and sustained phases of HPV were suppressed by SB-203580, but not by SB-202474 (both 2 mu M). Western blot analysis revealed that PGF sub(2 alpha ) (20 mu M) increased phosphorylation of p38 MAPK and of heat shock protein 27 (HSP27), and this was abolished by SB-203580 but not by SB-202474 (both 2 mu M). Endothelial denudation or blockade of endothelial nitric oxide (NO) synthase with N super( omega )-nitro-L-arginine methyl ester (L-NAME) significantly suppressed the relaxation of PGF sub(2 alpha )-constricted IPA by SB-203580, but not by SB-202474. Similarly, the inhibition of HPV by SB-203580 was prevented by prior treatment with L-NAME. SB-203580 (2 mu M), but not SB-202474, enhanced relaxation-induced by the NO donor S-nitroso-N-acetylpenicillamine (SNAP) in endothelium-denuded IPA constricted with PGF sub(2 alpha ). In alpha -toxin-permeabilized IPA, SB-203580-induced relaxation occurred in the presence but not the absence of the NO donor sodium nitroprusside (SNP); SB-202474 was without effect even in the presence of SNP. In intact IPA, neither PGF sub(2 alpha )- nor SNAP-mediated changes in cytosolic free Ca super(2+) were affected by SB-203580. We conclude that p38 MAPK contributes to PGF sub(2 alpha )- and hypoxia-induced constriction of rat IPA primarily by antagonizing the underlying Ca super(2+)-desensitizing actions of NO.