Renal actions of atrial natriuretic factor: modulation of effect by changes in sodium status and aldosterone

To examine the effect of changes in Na status on the renal response to atrial natriuretic factor (ANF), human ANF-(99-126) was infused into the renal artery of conscious sheep while Na replete, Na depleted, or Na loaded. The natriuretic response to ANF was attenuated during Na depletion and enhanced in Na-loaded animals. To demonstrate that the enhancement or attenuation of response was related to Na status rather than to the initial level of Na excretion, aldosterone was infused into the renal artery for 2 h to decrease Na excretion to a level inappropriately low for the animal's Na status (and not different from Na-depleted animals), and they were again challenged with ANF. Their response to ANF, however, was not significantly different from that in normal Na-replete animals but was significantly greater than that observed in Na-depleted animals. Similarly, Na-loaded animals treated with aldosterone had control Na excretion in the Na-replete range; however, their response to ANF was not significantly different from that of Na-loaded animals. The response to ANF was enhanced in sheep treated with aldosterone for 48 h, consistent with Na retention and hypervolemia, secondary to aldosterone treatment. The study demonstrates that Na status or some associated physiological parameter is an important determinant of the natriuretic response to ANF. The present series of experiments demonstrate that changes in aldosterone levels per se are not a determinant of the natriuretic response to ANF.