Inhibitory effect of C-type natriuretic peptide on spontaneous contraction in gastric antral circular smooth muscle of rat.

AIM: To investigate the effect of natriuretic peptides on gastric motility and its possible mechanism. METHODS: Spontaneous contraction of gastric antral circular muscle of rats was recorded by four channel physiograph. The concentration of cyclic guanosine monophosphate (cGMP) was measured by radioimmunoassay. The distribution of natriuretic peptide receptors (NPR) was analyzed by autoradiograph. RESULTS: NPR existed in different regions of rat stomach and its density was the largest in gastric antrum. Atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) all inhibited the spontaneous contraction of gastric antral circular smooth muscle. Among them, the inhibitory effect of CNP on the spontaneous contraction was the most potent and exhibited a dose-dependent manner. CNP-induced inhibition was diminished by LY83583 (a kind of inhibitor of guanylate cyclase) and potentiated by zaprinist (a kind of inhibitor of cGMP sensitive phosphoesterase). CNP markedly enhanced the concentration of cGMP in antral smooth muscle. The inhibitory effect of CNP on spontaneous contraction was also inhibited by tetraethylammonium (a nonselective potassium channel blocker, TEA). CONCLUSION: The distribution density of NPR is the most in gastric antrum. CNP significantly inhibits gastric motility in rat gastric antrum. The inhibitory effect occurs via a cGMP dependent pathway and potassium channel is also involved in the relaxation induced by CNP in gastric antrial circular smooth muscle of rat.