Effect Of Substance P On Sensation Afferent Function Of Gastrointestinal Tract And Heart Rate Variability

AIM: To investigate the effect of substance P on sensation afferent function of gastrointestinal tract and cardiac autonomic nervous function and the corresponding mechanism by the method of electrophysiology.METHODS:1. Forty SD rats were divided into 5 groups: control group(control), low dosage SP group(75ng/kg, SP-L), middle dosage SP group(150ng/kg, SP-M), high dosage SP group(300ng/kg, SP-H) and spantide II + 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.2. Forty SD rats were divided into 5 groups: control group, SP groups (5μg/kg,10μg/kg,20μg/kg) and spantideⅡplus SP group. An analysis of heart rate variability (HRV) was used to detect the changes of HRV parameters before and after intravenous injection of SP.RESULTS:1. Intravenous SP (150ng/kg, 300ng/kg) caused obviously increasing effect on the spontaneous afferent discharge(P<0.05) ;But high dosage SP caused decreasing effect on the gastric distention-induced afferent discharge of subdiaphragmatic vagus nerve(P<0.05). SpantideⅡ+ SP group significantly inhibited the effect of SP mentioned above.2. There were significant differences in most HRV parameters of three doses of SP. Mean heart period (MHP),absolute power of ultra-low frequency and high frequency band (APU, APH), total power value(TPV) and ratio of power in ultra-low to high frequency band( RUH) increased, while mean heart rate(MHR), chaos intensity (HCC) decreased during the 30 minutes. Each peak amplitude of HRV parameters went great and showed ahead with increasing doses of SP. There were significant changes in each parameters between spantideⅡplus SP and high dose of SP group.CONCLUTION:1. SP elicits excitatory effect on the spontaneous afferent discharge,and the effect may show dose dependent of 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 NK-1 receptor distributed in the stomach,and gastrointestinal sensation may input mainly via vagal afferent nerve.2. After intravenous injection different doses of SP, both cardiac sympathetic nervous system activity and parasympathetic nervous system activity increase, and cardiac autonomic nervous function becomes instable and unbalanced. The effect may show dose dependent of SP, and it is possibly mediated by neurokinin-1(NK-1) receptor.