Neuronal norepinephrine as mediator for ouabain-induced smooth muscle contraction.

With some latency, ouabain (10(-6)--10(-5) M) induced a long-lasting contractile response of the isolated vas deferens of the guinea-pig. The ouabain-induced contraction was potentiated by pretreatment with tropolone, whereas it was prevented by pretreatment with cocaine, bretylium, reserpine or phentolamine. The response was unaffected byatropine, methysergide and tetrodotoxin. Ouabain, perfused into the isolated tissue, enhanced dose-dependently the release of norepinephrine into the medium. However, this enhancement of norepinephrine release was prevented by reserpine or by removal of Ca from the medium. These findings support the hypothesis that the ouabain-induced contraction of vas deferens might be due to norepinephrine released from the adrenergic nerve ending granules through a Ca2+-dependent process.