COMPARISON OF CORELEASE OF NORADRENALINE AND ATP EVOKED BY HYPOGASTRIC NERVE-STIMULATION AND FIELD STIMULATION IN GUINEA-PIG VAS-DEFERENS

Contractions and overflow of tritium and ATP elicited by hypogastric n erve stimulation (HNS) and field stimulation (FS) were studied in the guinea-pig isolated vas deferens preincubated with [H-3]-noradrenaline . ATP was measured by means of the luciferin-luciferase technique. HNS and FS elicited contraction, tritium overflow and ATP overflow. HNS a t supramaximal current strength produced smaller responses than did FS at supramaximal current strength (210 pulses/7 Hz). Supramaximal HNS and submaximal FS were used in the remainder of the study. Prazosin (0 .3 mu mol/l) reduced contractions and the overflow of ATP elicited by both HNS and FS; the evoked overflow of tritium was not changed (210 p ulses/7 Hz). Combined administration of prazosin (0.3 mu mol/l) and su ramin (300 mu mol/l) abolished contractions and reduced the overflow o f ATP elicited by both HNS and FS slightly more than did prazosin alon e; tritium overflow again was not changed (210 pulses/7 Hz). Contracti ons, tritium overflow and ATP overflow increased with the frequency of both HNS and FS (from 7 to 25 Hz; 210 pulses); the increase in ATP ov erflow with frequency was more marked than the increase in tritium ove rflow. The preferential increase of ATP overflow with the frequency of HNS and FS persisted in the combined presence of prazosin (0.3 mu mol /l) and suramin (300 mu mol/l). The study confirms for HNS, a more phy siologic way of sympathetic nerve stimulation, several observations pr eviously obtained with FS. First, HNS-evoked ATP release is detectable as an overflow of ATP into the superfusion fluid. Second, a large par t of the HNS-evoked release of ATP is postjunctional in origin, due to activation of postjunctional alpha(1)-adrenoceptors and presumably P- 2-purinoceptors. Third, the average neural release of ATP per pulse fa cilitates with the frequency of stimulation to a greater extent than t he average release of noradrenaline per pulse.