EFFECT OF 8-SULFOPHENYL THEOPHYLLINE ON ENDOGENOUS NORADRENALINE RELEASE FROM SYMPATHETIC-NERVES OF THE RABBIT EAR ARTERY

1. The release of endogenous noradrenaline (NA) and adenyl purine (ATP , ADP, AMP and adenosine) from the rabbit ear artery, evoked by electr ical stimulation (ES; 16 Hz), was examined. 2. ES evoked a significant release of NA and adenyl purine; the ratio of the amount of total pur ine released to NA released was approximately 180 on a molar base. 3. ES-evoked purine release was significantly reduced by the denudation o f the endothelium and abolished by the alpha(1)-adrenoceptor antagonis t, prazosin (1 mu mol/L). 4. ES-evoked NA release was significantly re duced by a P-1-purinoceptor antagonist, 8-sulfophenyl theophylline (8S PT). Purine release was slightly reduced by 8SPT. 5. These results sug gest that endogenous NA released by ES results in the release of a lar ge amount of purine, which may, in turn, increase the release of NA by acting on prejunctional purinoceptors on sympathetic nerve terminals.