Vasopressin-reversible increase in angiotensin-converting enzyme in specific hypothalamic nuclei of Brattleboro rats

The activity of the angiotensin-converting enzyme (ACE) (kininase II, EC 3.4.15.1) was examined in 5 discrete hypothalamic nuclei of rats lacking vasopressin (homozygous Brattleboro rats, DI, di/di) and their corresponding controls (heterozygous Brattleboro rats, HZ, di/+, and Long Evans, LE, +/+ rats), with and without hormonal replacement with arginine-vasopressin (AVP). DI rats showed a vasopressin-reversible increased ACE activity when compared with LE controls, HZ rats showing intermediate activity. These changes occurred only in the supraoptic and periventricular hypothalamic nuclei, and were absent in other hypothalamic areas studied, including the paraventricular nucleus. These results provide biochemical evidence in support of previous anatomical and physiological data, for an interaction between the brain vasopressin and angiotensin systems in discrete hypothalamic nuclei, and suggest that vasopressin could regulate the formation of brain angiotensin II by modulating the activity of the converting enzyme.