Influence of methylene blue and oxyhemoglobin on mammalian vascular responses to sodium nitroprusside and nitroglycerin.

Vasodilatory responses to sodium nitroprusside were compared with those to nitroglycerin in helical strips of blood vessels isolated from dogs, humans, monkeys, rats and guinea-pigs. Sodium nitroprusside relaxed arterial and venous strips contracted with prostaglandin F2 alpha in a dose-related manner, as did nitroglycerin. Relaxant responses to sodium nitroprusside and nitroglycerin were significantly greater in dog coronary arteries than in the mesenteric arteries. Tachyphylaxis developed upon repeated applications of nitroglycerin but not of sodium nitroprusside. In rat and guinea-pig aortae, relaxant responses to sodium nitroprusside and nitroglycerin were markedly suppressed by treatment with methylene blue or oxyhemoglobin. In dog arteries and veins, treatment with oxyhemoglobin significantly inhibited relaxant responses to sodium nitroprusside and nitroglycerin. On the other hand, treatment with methylene blue did not inhibit responses to sodium nitroprusside but markedly suppressed those to nitroglycerin in dog blood vessels as well as in human gastroepiploic and monkey mesenteric arteries. It is concluded that dog and primate blood vessels do not develop tolerance to repeated applications of sodium nitroprusside and that sensitivity of soluble guanylate cyclase to methylene blue may differ in blood vessels from different mammals (dog and primate vs rat and guinea-pig).