A study on the release mechanism of vasopressin and oxytocin

The changes in plasma levels of arginine-vasopressin (AVP) and oxytocin (OXT) of rabbits by intraventricular administration of various drugs and their effects on the release of both hormones from the isolated posterior pituitary of rats were examined. An intraventricular injection of hypertonic saline, carbachol, angiotensin II, prostaglandin E2 or histamine to a rabbit increased the concentrations of plasma AVP and OXT, whereas serotonin decreased their plasma levels. Noradrenaline increased the concentration of OXT, but not that of AVP. Dopamine did not significantly affect the plasma level of either hormone. The release of AVP and OXT from the posterior pituitary fragments of rats was stimulated by changing the osmolality of the perfusion medium in vitro. Perfusion with medium containing dopamine suppressed the release of both hormones. However, the other bioactive amines and the drugs mentioned above did not affect the release of AVP and OXT.