1. Artificial cerebrospinal fluid was perfused through the cerebral ventricles of conscious rats. A basal secretion rate of 16 ± 3 × 10—15 mol of immunoreactive angiotensin 11/min was calculated for intact rats.
2. Most of the immunoreactive angiotensin II consisted probably of the heptapeptide or pentapeptide angiotensin II fragments.
3. The pressor responses to intraventricular perfusions of angiotensin II were normal in Long—Evans rats, virtually absent in rats homozygous for hereditary hypothalamic diabetes insipidus, irrespective of whether they were injected with vasopressin tannate or not, and intermediate in rats heterozygous for hypothalamic diabetes insipidus.
4. The results suggest that the pressor response to intraventricular angiotensin II is related to the release of vasopressin.