| Natriuretic peptides are a kind of polypeptide family with many bioactivities and they exert physiologic functions as hormone or neurotransmitter. Up to now, NPs include atrial natriuretic peptide(ANP), brain natriuretic peptide(BNP), C-type natriuretic peptide(CNP) and dendroaspis natriuretic peptide(DNPX Mcrurus natriuretic peptide(MNP) and Ventricular natriuretic peptide(VNP). They are distributed all over the body and exert natriuretic-diuretic, vasorelaxation and other functions designed to lower blood pressure and to control electrolyte homeostasis and so on. Since immunioactivity was found in the stomach and small intestine of rats, the investigation of the relationship between NPs and gastrointestinal function was preluded. The study about physiologic functions of NPs mainly focused on gastric absorption, secretion and intestinal motility, but a series of studies of NPs in regulating gastric smooth muscles motility has not been reported. The aim of the present study is to investigate the effect of CNP on gastric motility and its ion mechanism.In this present study, the distribution of NPs was observed by autoradiography technique and the effect of CNP on the spontaneous motility of gastric smooth muscles was investigated by four channel physiograh in vitro. To investigate the effect of CNP on calcium-activated potassium currents( /K(Ca)) in the gastric circular smooth muscle of guinea-pigs, the whole cell patch clamp technique was used in single smooth muscle cell.The results are as below:1. By using the autoradiograph technique, It was investigated that NP distributed in the mucous and smooth muscle layer of the gastric antral, gastric body and gastric fudus, but the density of the distribution was the biggest in smooth muscle layer of gastric antral in rats.2. Effect of NPs on spontaneous motiliiy of gastric smooth muscle(1) ANP, BNP and CNP all inhibited the spontaneous motility of the gastric antral smooth muscle in rat and the effect of CNP was most potent.(2) CNP (0.1 uM) inhibited spontaneous motility of the gastric antral circular smooth muscles of rats, guinea-pigs and humans. The inhibitory amplitude of the circular smooth muscle was 58.23%?.21%, 66.32%?.32% and 100.00%?.00%, respectively. CNP completely inhibited the spontaneous motility of the gastric antral longitudinal smooth muscle.(3) The effect of CNP on the gastric body smooth muscles exhibited double reactions in rats and guinea-pigs. CNP induced a relaxation at first and then potentiated spontaneous contraction (rebound contraction) in the guinea-pigs. After the muscle strip was pretreated with atropine(luM ), the rebound contraction was eliminated; however, in rats, the CNP only induced a transient and slight relaxation. After the muscle strips were pretreated with atropine, the transient and slight relaxation was replaced by long term and complete inhibition.(4) CNP inhibited spontaneous motility of the gastric fundus smooth muscle in guinea-pigs and rats. The inhibitory content was 76.77% ?.21% and 95.87% ?4.12%, respectively. CNP completely inhibited the spontaneous motility of the gastric antral longitudinal smooth muscle.(5) CNP-induced inhibition on the longitudinal smooth muscle was more potent than on the circular smooth muscle of the same position in the same animal. The inhibitory percentages of CNP on the circular smooth muscle in the gastric antrum, body and fudus were 58.23% ?6.21%, 57.21% ?.32% and 76.77% ?6.21% respectively in guinea-pigs. However, the inhibitory percentages of CNP on the longitudinal smooth muscle were 100.00%?.00%, 68.66%?.55% and 100.00%?0.00%. The inhibitory percentages of CN..' on the circular smooth muscle were 66.32%?.32%, 94.91%?.65% and 95.87%?.12% respectively and in the gastric antrum, body and fundus on the longitudii al smooth muscle were 100% ?.00%, 94.34%?.65% and 100%?.00%, respectively in rat.3. Relationship between NP-induced relaxation and cGMP (the secondmessenger).(1) Using LY83583(0.1uM), a guanylate cycla...
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