Airways of a hyperresponsive rat strain show decreased relaxant responses to sodium nitroprusside

The aim of the current studies was to investigate the possibility that a decreased relaxant response to nitric oxide (NO) might contribute to strain-related differences in airway responsiveness in the rat. Isolated tracheal rings from hyperresponsive. Fisher rats were confirmed to be more responsive to carbachol [mean effective concentration (EC50) = 2.45 x 10(-7) M] than those from Lewis (EC50 = 3.60 x 10(-7) M, P < 0.03) and ACI (EC50 = 3.85 x 10(-7) M, P < 0.01) rats. Sodium nitroprusside (SNP), a NO donor, caused relaxation of the carbachol (10(-6) M) contracted tracheal rings, but the half-maximal inhibition concentration (IC50) SNP in Fisher rats (5.60 x 10(-6) M) was significantly higher than in Lewis (1.34 x 10(-6) M, P < 0.001) and ACI rats (1.13 x 10(-6) M, P < 0.0005). The inhibitory effect of SNP on airway responsiveness to inhaled methacholine (MCh) in vivo was also less pronounced for Fisher than Lewis rats. SNP induced an accumulation of guanosine 3',5'-cyclic monophosphate (cGMP) in cultured tracheal smooth muscle cells (TSM). Fisher TSM produced less cGMP on exposure to SNP compared with TSM from ACI (P < 0.01) and Lewis (P < 0.0001) rats. A decreased guanylyl cyclase activity may account for the impaired relaxant effect of SNP in Fisher rats.