FURTHER-STUDIES OF THE SITE AT WHICH ANGIOTENSIN-II ACTS IN THE CENTRAL-NERVOUS-SYSTEM TO INHIBIT THE SECRETION OF PROLACTIN

Intraventricular renin increases dopamine turnover in the tuberoinfund ibular neurons of rats, and intraventricular angiotensin II (AII) inhi bits prolactin secretion. To explore the possibility that the inhibiti on is mediated by AII-containing nerve fibers that end directly on dop amine-secreting neurons in the arcuate nucleus, we stained this nucleu s immunocytochemically for AII and tyrosine hydroxylase in female rats . We also performed in vitro receptor autoradiography for AII receptor s. There were nerve fibers that contained AII immunoreactivity in the arcuate nucleus, and many of these nerve fibers were closely apposed t o the cell bodies of neurons that contained tyrosine hydroxylase immun oreactivity. In rats sacrificed during proestrus, AII receptors were r eadily detected in the arcuate nucleus, with the highest concentration in the dorsal portion of the nucleus, the area where there are the mo st cell bodies of dopaminergic neurons. The data support the hypothesi s that brain AII inhibits prolactin secretion by directly stimulating the cell bodies of arcuate neurons that secrete dopamine into the port al-hypophyseal vessels.