Oxytocin release is inhibited by opiates from the neural lobe, not those from the intermediate lobe.

Previous experiments have shown that the amount of oxytocin released by electrical stimulation from an isolated rat neurointermediate lobe is about doubled in the presence of the opiate antagonist naloxone. To test whether the opiates from the intermediate lobe inhibit the release of oxytocin, we performed similar experiments on the isolated neural lobe, after almost total removal of intermediate lobe tissue. The potentiating effect of naloxone upon oxytocin release was undiminished, suggesting that the endogenous opiate responsible for inhibiting oxytocin secretion comes from the neural lobe itself.