Heparin shows blood pressure lowering effect in hypertensive patients and animal models. The present study examined the effect of heparin on vasoconstrictor endothelin-1 (ET-1) production in cultured human umbilical vein endothelial cells (ECs) to elucidate the mechanism of antihypertensive effect of heparin. Heparin suppressed both basal and thrombin-stimulated ET-1 mRNA expression paralleled with a decrease in ET-1 peptide release in a dose-dependent manner. Heparin concomitantly enhanced nitric oxide (NO) formation measured by N02/ NO3 levels and cGMP production in ECs. These enhancements were more marked when ECs were stimulated by thrombin. However, these heparin's effects were blunted in the presence of endothelium-derived nitric oxide (EDNO) synthesizing inhibitor NG-monomethyl L-arginine. Therefore, these results suggest that suppression of ET-1 production by heparin is EDNO
Strong potassium channel-activating effects were found among a series of novel 4-substituted 3,4-dihydro-2H-1,4-benzoxazine derivatives. The key step in preparation was the nucleophilic substitution of 3,4-dihydro-2H-1,4-benzoxazine (3) with activated halogenopyridines, such as halogenopyridine N-oxides (15a--c) and the borane adduct (15d) of 4-bromopyridine. Structure-activity relationship studies identified 2-(3,4-dihydro-2,2-dimethyl-6-nitro-2H-1,4-benzoxazin-4-yl)pyridin e-1-oxide (16a: YM934) as the optimal compound. This compound (16a) showed a more potent oral antihypertensive effect than cromakalim in conscious spontaneously hypertensive rats.
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