The effect of ouabain on noradrenaline output from peripheral adrenergic neurones of isolated guinea-pig vas deferens.

1. The effect of ouabain on the noradrenaline output from peripheral adrenergic neurones has been studied using isolated guinea-pig vasa deferentia.2. Exposure to ouabain (10(-4)M) causes a gradual increase in the noradrenaline output. The effect occurs after a delay of 20 min and reaches a maximum during the period from 40-60 min.3. In the absence of external Ca, exposure to ouabain fails to produce an increase in the noradrenaline output. However, the reintroduction of Ca (2.5 mM) after a 1 hr exposure to ouabain in Ca-free media causes a rapid rise in noradrenaline output which reaches a maximum within the first 20 min.4. After a 1 hr exposure to a low concentration of ouabain (10(-5)M) the reintroduction of Ca is almost ineffective in increasing the noradrenaline output. When the concentration of ouabain is increased, the reintroduction of Ca becomes effective and causes a maximum effect with 10(-4)M ouabain. In the presence of a constant amount of ouabain (10(-4)M) the noradrenaline output induced by the reintroduction of Ca increases over the range 0.2-2.5 mM.5. In the presence of ouabain (10(-4)M) the Ca-induced noradrenaline output increases in a linear fashion with increasing Na concentrations from 25 to 143 mM, as long as NaCl is replaced with equimolar choline chloride or isotonic sucrose.6. In the presence of the lowest effective concentration of sodium (25 mM) the noradrenaline output induced by the reintroduction of Ca after a 1 hr exposure to ouabain is potentiated by LiCl. However, in the complete absence of Na(+) ions, there is no Li-dependent increase in the Ca-induced noradrenaline output.7. It is suggested that ouabain may cause an increase in noradrenaline output by an effect on the Na-dependent Ca influx system.