Effect of dopamine injection into the anteroventral third ventricular region and the paraventricular nucleus on vasopressin secretion in conscious rats.

To investigate the role of dopamine receptors situated in the paraventricular nucleus and the anteroventral third ventricular region in regulating vasopressin release, responses of plasma AVP and its controlling factors to injections of dopamine into these regions and the lateral cerebral ventricle were examined in conscious rats. The injections of 156 nmol (30 micrograms) dopamine into the cerebral ventricle produced transient rises in plasma AVP 5 min later. When the dose of dopamine was reduced to 26 nmol (5 micrograms), the increase in plasma AVP was not provoked any more. However, injections of 26 nmol dopamine into the paraventricular nucleus greatly augmented plasma AVP 5 and 15 min later. This dose of dopamine was without effect on plasma AVP when injected into the anteroventral third ventricular region, including the organum vasculosum lamina terminalis, median preoptic nucleus, medial preoptic area and the periventricular preoptic nucleus. These dopamine administrations in the cerebral ventricle, paraventricular nucleus and the anteroventral third ventricular region did not significantly change AVP-controlling factors such as plasma osmolality, sodium and arterial pressure. On the basis of these results, we conclude that dopamine receptors in the paraventricular nucleus may function to facilitate AVP secretion, whereas those in the anteroventral third ventricular region may not play an important role in the regulation of AVP release.