Intracerebroventricular (i.c.v.) administration of human atrial natriuretic factor (ANF), fragment 1-25, in the dose range 3 to 20 micrograms/kg did not alter resting arterial pressure or heart rate in rats anesthetized with chloralose/urethan (60:600 mg/kg i.p.), while angiotensin II (ANG II), 1 microgram/kg, produced a significant increase in arterial pressure after i.c.v. application. This pressor effect induced by ANG II was abolished by simultaneous administration of ANF (3 micrograms/kg i.c.v.). In isolated strips of rabbit aorta preconstricted with ANG II (10 nM), ANF caused a dose-dependent relaxation. In intact rats, the increase in blood pressure following intravenously administered ANG II (0.1 and 1 microgram/kg) was not altered by the highest dose of ANF (20 micrograms/kg) given intracerebroventricularly. These results suggest that atrial peptides may play an important role in the regulation of blood pressure by interacting with both the central and peripheral actions of ANG II. Inhibition of the central pressor action of angiotensin by ANF appears to be independent of any direct peripheral effect of the atrial peptides.

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