Objective:To study the effect of substance P on sensation afferent of gastrointestinal tract and the corresponding mechanism. Methods:Forty SD rats were divided into 5 groups:control group

low dosage SP group(75 ng/kg)

middle dosage SP group(150ng/kg)

high dosage SP group(300 ng/kg)and spantideII+SP group.The electrophysiological method was used to record the change of spontaneous and gastric distention-induced afferent discharge of subdiaphragmatic vagus nerve in each group.Results:Intravenous SP (150 ng/kg

300 ng/kg)caused significantly increasing effect on the spontaneous afferent discharge(P<0.05)

high dosage SP caused decreasing effect on the gastric distention-induced afferent discharge of subdiaphragmatic vagus nerve(P<0.05).SpantideⅡ+SP significantly inhibited the effect of SP mentioned above.Conclusion:SP elicits excitatory effect on the spontaneous afferent discharge

and the effect may show dose dependent on SP.SP elicits inhibitory effect on gastric-distention induced discharge of subdiaphragmatic vagus nerve.The action of exogenous SP afferent discharge of subdiaphragmatic vagus nerve is possibly mediated by NK1 receptor distributed in the stomach.