A study on the mediators of antidromic vasodilatation elicited by sciatic nerve stimulation in cats.

This study was undertaken to ascertain whether a purinergic substance, histamine, dopamine or prostaglandins are mediators involved in antidromic vasodilatation. This type of vasodilatation was elicited by stimulation of the distal end of sectioned sciatic nerve at 40 V with 2 msec pulses for 30 sec in autoperfused hindlimb of reserpine-pretreated and anesthetized cats. Artificial respiration was applied because of curarization that was done to abolish the vascular responses due to contractions of striated muscle. Stimulation of sciatic nerve caused a sustained vasodilatation which was more marked at a frequency of 30 pps. The responsiveness of the perfused vessels to vasodilator stimuli tended to increase by increasing the duration of perfusion as controlled by papaverine administration at certain intervals. Both mepyramine and subsequent administration of metiamide did not produce any change in the vasodilator response to nerve stimulation though they blocked the vasodilator response to histamine. Dopamine injected intra-arterially elicited a pressor response which was reversed into a vasodilator one by phentolamine. This vasodilator response to dopamine tended to be reduced by haloperidol which produced either no change or a slight increase in antidromic vasodilatation. Pretreatment with theophylline to antagonize the likely purinergic mediators or with indomethacin to inhibit the synthesis of prostaglandins had no effect on antidromic vasodilatation elicited by sciatic nerve stimulation. These results suggest that the above-mentioned compounds might not be involved in antidromic vasodilatation.