Relaxant effect of C-type natriuretic peptide on guinea-pig tracheal smooth muscle

Abstract

The relaxant effects of the C-type natriuretic peptide (CNP) on guinea-pig tracheal smooth muscle were investigated. CNP (10(-8)-10(-5) mol/l) induced dose-dependent relaxant effects on the resting tone of tracheal smooth muscle with EC50 of 3.6 +/- 0.8 x 10(-6) mol/l (mean +/- SE). CNP caused a dose dependent increase in the tissue cyclic GMP level in tracheal smooth muscle (191 +/- 10 fmol/mg protein in control, 583 +/- 33 fmol/mg protein at 10(-7) mol/l, 688 +/- 56 fmol/mg protein at 10(-6) mol/l, 1091 +/- 167 fmol/mg protein at 10(-5) mol/l). Tissue cyclic GMP levels showed a peak at 1 min. Relaxation of the tracheal smooth muscle began at 1 min, reaching peak value at 5 min after the perfusion of CNP (10(-5) mol/l). Elevations in cyclic GMP preceded the relaxation of tracheal smooth muscle. These results suggest that CNP may be a novel potent relaxant in tracheal smooth muscle and that its relaxant effect may be mediated by cyclic GMP levels.