Co-Regulation of Tracheal Tone by cyclic AMP- and cyclic GMP-Dependent Mechanisms

The regulation of guinea pig tracheal muscle tone by cyclic AMP-dependent and cyclic GMP-dependent relaxant mechanisms was investigated by studying the tracheal relaxant activities of for-skolin, nitroprusside, N#{176}-2‘-O-dibutyryl-cyclic AMP and 8-bro-moguanosine-cyclic GMP. In carbachol (3 x 1 0 M)-contracted isolated tracheal rings, N#{176}-2’-O-dibutyryl-cyclic AMP and 8-bro-moguanosine-cyclic GMP each caused biphasic relaxation re-sponses, which consisted of an acute relaxation followed by a sustained but lesser degree of relaxation. The biphasic nature of this response is suggested to result from a functional counter-balancing of cyclic nudeode-dependent relaxant mechanisms and the contractile mechanisms stimulated by carbachol. The sensitivity of carbachol-contracted tracheal nngs to forskolin and nitroprusside (activators of adenylate and guanylate cyclase