Object: To observe the influence of subarachnoid microinjection of SP and L-arginine on the threshold of electrical stimulation of cat's inferior cardiac nerve evoking myoelectricity around "Tianquan" (PC2) point and analyze their roles in this process.

Methods: 24 healthy cats of both sexes weighing 2.0-3.2 Kg were used in this work. After anaesthesia with the mixed solution of urethane (50mg/kg) and chloralose (500mg/kg), the C8-Tl spinal cord was exposed and the inferior cardiac nerve (CN) and the cardiac nerve (CN) were carefully dissected from the first rib for stimulation. The parameters were: stimulation strength 1 mA, frequency lHz, double pulses with an interval of 4ms. Two acupuncture need1es were inserted in "Tianquan" point to record the electromyography (EMG). After stabilization of the myoelectrical activity the threshold of myoelectrical response in "Tianquan" was measured as the control value by electrical stimulation of ICN. Then the response threshold values at 2', l0', 20' and 30' after subarachnoid microinjection of 8μL SP into C8-Tl spinal cord was analyzed. Afterwards,i.e. after an interval of 30 minutes, subarachnoid injection of 8μl DPDPDT was given and the changes of EMG response were measured. The administration of L-arginine and its antagonist L-ANA and the resultant changes of EMG were also observed.

Results: (1) Subarachnoid microinjection of L-arginine could distinctly cause the threshold to increase by 0.l4 mA in average (MiASE, before microinjection 1.39iA0.08 mA, after microinjection 1.53iA0.l2 mA, P<0.05f=the same below) and the effect maintained for re1atively long duration. It could not completely recover in 30 minutes; On the contrary its antagonist L-N'NA could turn the threshold to normal level in 20 minutes (1.50iA0.46 mA - 1.40iA0.43 mA); (2) SP antagonist DPDPDT could cause the threshold value to decrease by 0.06 mA in average(l.36iA0.l0 mA - 1.30iA0.08 mA, P<0.05); But SP could reverse the decrease in short period of time (l .33 iA0.09 mA - l.42iA0.1l mA). The threshold might restore in 2 minutes after the injection. The difference had distinct statistical significance (P<0.05).

Conclusion: SP and L-arginine (NO)were involved in the correlation between "Tianquan" acupoint and the heart, and maybe contribute to the effect of acupuncturing points of the along Pericardium Meridian on treating cardiovascular diseases.

By Zhang Jianliang Chen Shuping, Liu Junling & Gao Yonghui.