Centrally administered atrial natriuretic factor inhibits central angiotensin-induced natriuresis

Atrial natriuretic factor (ANF) and angiotensin II (ANG II) have been demonstrated in close vicinity in forebrain areas involved in the central fluid and electrolyte regulation. Previous reports suggested an inhibitory effect of ANF on some of the central actions of ANG II, such as water intake and vasopressin release. In the present study in conscious, unrestrained, sodium-repleted rats we investigated the effects of intracerebroventricularly (i.c.v.) administered ANF (alpha r-APIII) on the central natriuretic action of ANG II. Urine was collected through a novel chronically implanted ureteral catheter. I.c.v. injections of ANG II (100 pg) produced a marked natriuresis of rapid onset without altering urinary volume or blood pressure. Pretreatment with ANF (100 pg, 1 ng, 100 ng i.c.v.) 5 min before ANG II dose-dependently antagonized the ANG II-induced natriuretic effect. The lowest dose caused approximately 50% reduction, the intermediate dose a complete abolition and the highest dose even a reversal of the ANG II-induced natriuretic effect to salt retention. Urinary volume and blood pressure were not altered by the combined treatment with ANG II and ANF. Our results support the idea of a functional antagonism between ANG II and ANF in the central fluid and electrolyte control.