Potentiation of lactation-induced oxytocin secretion by intracerebroventricular oxytocin in the conscious goat.

The release of oxytocin into the cerebrospinal fluid (CSF) and plasma of lactating goats was studied following implantation of cisternal and lateral ventricular cannulae. Hand milking was associated with a significant increase in plasma concentrations of oxytocin, but no change in plasma concentrations of vasopressin or CSF concentrations of oxytocin. Intracerebroventricular (i.c.v.) infusion of oxytocin itself (1 pmol/min for 60 min) had no effect on basal plasma levels of oxytocin. It did, however, markedly potentiate the milking-induced increase in plasma oxytocin above the levels achieved during i.c.v. infusion of artificial CSF alone. In the goat, therefore, milking results in a selective release of oxytocin into the plasma, and this release can be potentiated by the presence of increased concentrations of oxytocin in the CSF.