Atrial natriuretic peptide reverses angiotensin-induced venoconstriction in dogs

To determine whether atrial natriuretic peptide (ANP) can reverse angiotensin (ANG II)-induced venoconstriction, ANP was infused (0.3 micrograms.kg-1.min-1) in the presence of ANG II-induced hypertension in six ganglion-blocked dogs. ANG II was initially administered to increase mean arterial blood pressure (MAP) 50% above control. ANG II did not change heart rate or left ventricular rate of pressure development (LV dP/dt) but increased total peripheral vascular resistance (TPVR) and left ventricular end-diastolic pressure (LVEDP). Mean circulatory filling pressure (MCFP) increased, whereas cardiac output and venous compliance decreased. Unstressed vascular volume did not change, but central blood volume increased. ANP infusion during ANG II-induced hypertension resulted in a decrease in MAP, but TPVR did not change. There were no changes in heart rate or LV dP/dt. ANP decreased cardiac output further. LVEDP returned to base line with ANP. ANP also decreased MCFP and normalized venous compliance. There was no significant change in total blood volume, but central blood volume decreased. In summary, ANP can reverse the venoconstriction but not the arterial vasoconstriction produced by ANG II. The decrease in MAP was due to a decrease in cardiac output that resulted from venodilatation and aggravation of the preload-afterload mismatch produced by ANG II alone. Because TPVR did not change when MAP fell, we conclude that the interaction between ANG II and ANP occurs primarily in the venous circulation.