Central actions of atrial natriuretic polypeptides in spontaneously hypertensive and normotensive rats

The effects of intracerebroventricular (i.c.v.) administration of ANP on blood pressure and intakes of water and salt were examined, using conscious, unrestrained normotensive Wistar rats and spontaneously hypertensive rats (SHR). In normotensive rats, i.c.v. administration of alpha-rat ANP (alpha-rANP), alpha-human ANP (alpha-hANP), alpha-rANP (4-28) and alpha-rANP (5-28) at the dose of 1.5 nmol significantly attenuated water intake induced by i.c.v. injection of 0.1 nmol of angiotensin II (AII). Centrally administered alpha-hANP (5 micrograms) also attenuated AII-induced pressor response. Centrally injected alpha-hANP (1 microgram) produced a greater reduction of water intake after 24-hour water deprivation in SHR compared to control Wistar Kyoto rats (WKY). Central infusion of alpha-hANP for 1 week also reduced the salt appetite of SHR, as shown by two bottle preference test with 0.3 M NaCl solution and tap water, while it had no effect on drinking behavior of WKY. These results suggest the central antagonistic relationship of the ANP and renin-angiotensin systems and the possible involvement of brain ANP in the pathophysiology of genetically hypertensive rats.