Prostaglandin-versus alpha-adrenoceptor-mediated control of sympathetic neurotransmitter secretion in guinea-pig isolated vas deferens

Noradrenaline (NA) secretion of isolated superfused guinea-pig vas deferenswas studied by determination of total field stimulation-induced efflux of tritium, after preincubation with ³H-l-NA. The medium contained optimal concentrations of desmethylimipramine and normetanephrine to block local rebinding of free NA. Further addition of the two chemically different inhibitors of prostaglandin synthetase, 5,811,14 eicosatetraynoic acid or indomethacin, consistently enhanced the nerve stimulation-induced output of tritium at a frequency of 5/sec, but not at 10/sec. The α-adrenoceptor blocking agent, phenoxybenzamine further strongly elevated nerve stimulation-induced output of tritium. This rise was abolished by low concentrations of exogenous prostaglandin E₂. The results show that sympathetic neurotransmitter secretion in the guinea-pig vas deferens, during low frequency stimulation, is restricted by local formation of prostaglandin E. However and in addition, neurotransmitter secretion appears to be restricted by an α-adrenoceptor-mediated mechanism, which does not appear to depend on endogenous prostaglandin E as a chemical mediator.