Relaxation of guinea‐pig trachea by sodium nitroprusside: cyclic GMP and nitric oxide not involved

Open Access
Publisher Website
Google Scholar
Abstract
1 Sodium nitroprusside (SNP) completely relaxed the guinea-pig isolated, perfused trachea in a concentration-dependent manner. Although SNP was less potent by about 2 orders of magnitude, its maximal effect was 25% higher compared to isoprenaline. 2 SNP (3.2 μm) increased cyclic GMP levels by 300% and relaxed guinea-pig isolated, perfused trachea by 54%. The SNP-induced relaxations of the preparations were not affected by the guanylate cyclase inhibitor, methylene blue. Moreover, zaprinast, a cyclic GMP-specific phosphodiesterase inhibitor which was supposed to enhance SNP-induced relaxations, decreased the maximal relaxation by 22% (P < 0.001). 3 In contrast, 8Br-cyclic GMP (10 μm) increased the cyclic GMP levels by 1100% without inducing a marked relaxation. 4 SNP (10 μm) and S-nitroso-N-acetylpenicillamine (SNAP; a direct donor of nitric oxide; 10 μm), relaxed the tissues by 75% and 25%, respectively, without any nitric oxide (NO) release by SNP (< 1 pmol 100 μl−1), but a substantial NO release by SNAP (560 pmol 100 μl−1). 5 It is concluded that the SNP-induced tracheal relaxations are probably not mediated by cyclic GMP and NO.