Objective:To study the effect of secretin on subdiaphragmatic vagal afferent response by gastric distension. Methods: Experiments were performed on anesthetized rats. The sensory impulses of subdiaphragmatic vagal nerve were recorded using a window discriminator. Through a midline abdominal incision

a polyethylene cannula (1.0mm ID) for duodenal infusion was inserted into the proximal duodenum 0.5mm distal to the pylorus.Another cannula was placed into jejunum 20 cm distal to the ligament of Treitz.Gastric distension was produced by injecting saline at 37℃ into a small balloon via a polyvinyl tube.Results:Intravenous injection of secretin in a dose of 5.0 pmol/kg/h inhibited significantly the response of afferent discharges induced by gastric distension( n=7

P <0.05)

while lower dose secretin (2.5pmol/kg/h iv.) failed to affect this response. The vagal afferent were further suppressed when the dose of secretin was increased to 10pmol/kg/h ( n=7

P <0.01). The inhibitory effect of 10 pmol/kg/h was earlier and larger than 5.0 pmol/kg/h( P <0.05)

but no significance was demonstrated after 10 min ( P >0.05). It showed that exogenous secretin in a dose of 5.0pmol/kg/h

in the physiological dose range

played an inhibitory effect. 0.03N HCl was infused intraduodenally at 9 ml/h for 20 min in anesthetized rats with gastric cannulas

ligation of the pylorus

respectively.0.1 ml of a rabbit antisecretin serum (titer=l:l

000

000) was injected intravenously in a bolus 20～40min before HC1 was administered. During the duodenal infusion of 0.03N HCI the gastric distension-vagal afferent responses were suppressed significantly.( n=8

P <0.05). It was reversed by antisecretin serum ( P <0.01). Conclusion:These observations provide a direct electrophysiological evidence that vagal afferent pathway plays an important role in the gastric-distension inhibition by exo- & endogenous secretin.