Effects of atrial natriuretic factor on pressor responsiveness to angiotensin II, norepinephrine, and vasopressin in conscious sheep.

The effects of pretreatment with atrial natriuretic factor (ANF) on the pressor responsiveness to injections of angiotensin II (ANGII), arginine vasopressin (AVP), and norepinephrine (NE), as well as the effect of pretreatment with ANGII on the hypotensive responses to ANF injection were studied in conscious sheep. The hemodynamic effects of ANF infusion (100 micrograms/h for 60 min) were also examined in animals pretreated with the angiotensin-converting enzyme (ACE) inhibitor, captopril. Infusion of ANF attenuated the pressor responsiveness to exogenous AII and NE, but caused no significant change in the blood pressure increases produced by vasopressin. In contrast, infusion of AII had no effect on the immediate hypotensive response to ANF injection. Infusion of ANF for 60 min produced similar hemodynamic actions in sheep during ACE inhibition as compared with the responses observed in normal sheep, although the reduction in cardiac output and increase in calculated total peripheral resistance was attenuated. Infusion of captopril increased plasma concentration of renin (PRC), and infusion of ANF produced no further change in PRC. In conclusion, the short-term cardiovascular responses to ANF infusion in conscious sheep are not mediated solely by inhibition of the renin-angiotensin system. However, ANF attenuates the pressor actions of pharmacologic doses of exogenous ANGII and NE. In contrast, the vasodepressor response to exogenous ANF injection was not altered in animals receiving ANGII infusion. This study suggests that ANF may be important in regulating the effects of endogenous vasoconstrictor hormones on blood pressure (BP).