Inhibitory effect of prostaglandin E2 on noradrenaline secretion from sympathetic nerves as a function of external calcium

The calcium dependence of the inhibitory effect of prostaglandin E₂ on sympathetic neurotransmitter secretion was studied in isolated superfused field stimulated guinea-pig vas deferens, by determination of the nerve stimulation induced rise in efflux of total tritium after preincubation of the tissue with tritium-labelled 1-noradrenaline. Reuptake of noradrenaline was blocked by desipramine and normetanephrine, added to the medium. Reduction of the calcium in the superfusion medium strongly depressed the nerve stimulation induced rise in efflux of tritium. Addition of the alpha-adrenoceptor blocking drug phentolamine markedly raised the efflux of tritium on nerve stimulation, even at low calcium. The inhibitory effect of prostaglandin E₂ on nerve stimulation induced rise in efflux of tritium was inversely related to the calcium concentration. The results are consistent with the possibility that prostaglandin E₂ depresses neural secretion by facilitating efflux of intraaxonal calcium.