Atrial natriuretic factor-specific antibody as a tool for physiological studies. Evidence for role of atrial natriuretic factor in aldosterone and renal electrolyte regulation

Renal function in high-output heart failure in rats: role of endogenous natriuretic peptides

The physiologic and pathophysiologic importance of natriuretic peptides (NP) has been imperfectly defined. The diminished renal responses to exogenous atrial NP in heart failure have led to the perception that the endogenous NP system might be less effective and thus contribute to renal sodium retention in heart failure. This study tests the hypothesis that in experimental heart failure, the renal responses to an acute volume load are still dependent on the NP system. The specific antagonist HS-142-1 was used to block the effects of NP in a model of high-output heart failure induced by an aortocaval shunt. Plasma cGMP levels and renal cGMP excretion were significantly lower in shunted and sham-operated rats receiving HS-142-1, compared with vehicle-treated controls, indicating effective blockade of guanylate cyclase-coupled receptors. Baseline sodium excretion and urine flow rate were lower in HS-142-1-treated sham-operated rats (15.2+/-1.1 microl/min versus 27.5+/-3.1 microl/min with vehicle, P < 0.001) and in HS-142-1-treated shunted rats (8.1+/-1.3 microl/min versus 19.9+/-2.3 microl/min with vehicle, P < 0.001). After an acute volume load, the diuretic and natriuretic responses were attenuated by HS-142-1 in control and shunted rats. The renal responses were reduced by HS-142-1 to a significantly greater extent in shunted rats than in control rats. HS-142-1 did not induce any significant systemic hemodynamic changes in either group, nor did it alter renal blood flow. However, the GFR in HS-142-1-treated shunted rats was lower than that in vehicle-treated shunted rats, both at baseline (0.6+/-0.3 ml/min versus 2.1+/-0.4 ml/min with vehicle, P < 0.05) and after an acute volume load (1.2+/-0.4 ml/min versus 2.6+/-0.4 ml/min with vehicle, P = 0.01), whereas no such effect was observed in control rats. These data indicate that the maintenance of basal renal function and the responses to acute volume loading are dependent on the NP system. The NP seem to be of particular importance for the maintenance of GFR in this model of experimental heart failure. These observations provide new insights into the importance of the renal NP system in heart failure.

Effect of monoclonal anti-ANP antibodies on the acute functional adaptation to unilateral nephrectomy

The role of endogenous atrial natriuretic peptide (ANP) in the immediate response of sodium excretion to unilateral nephrectomy (UNX) was investigated in anesthetized euvolemic rats through measurement of UNX-induced change in plasma ANP concentration and the response of the remaining kidney to UNX following administration of monoclonal anti-ANP antibodies. The circulating ANP levels almost tripled (from 23 +/- 4 to 66 +/- 13 fmol/ml, P < 0.01) within two minutes after UNX, whereas no change resulted from sham intervention. In the control group receiving vehicle injection, UNX resulted in a twofold increase in urinary sodium excretion (from 1.39 +/- 0.25 to 2.88 +/- 0.28 mumol/min, P < 0.01) related to a decrease in the fractional reabsorption of sodium at both proximal and distal sites (estimated from fractional excretion of lithium). Urinary excretion of cyclic guanosine 3'-5'-monophosphate (cGMP) increased as well, but glomerular filtration rate did not change. In addition, UNX was associated with a short-lived (< 20 min) rise in systemic arterial pressure and a transient fall in right atrial pressure. Administration of monoclonal anti-ANP antibodies totally prevented the UNX-associated natriuresis by blunting both proximal and distal tubular reabsorption of sodium, and suppressed the rise in urinary cGMP excretion following UNX. The duration of the post-UNX increase in arterial pressure was longer when compared to values observed in controls. These observations indicate that ANP release is stimulated after uninephrectomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of endogenous atrial natriuretic factor in the regulation of fetal cardiovascular and renal function

The purpose of the present study was to determine whether endogenous atrial natriuretic factor participates in the maintenance of normal vascular pressure and renal function in ovine fetuses at 128 to 130 days' gestation. Circulating atrial natriuretic factor in the fetus was immunoneutralized by an intravenous bolus injection of an atrial natriuretic factor antiserum at a dilution of 1:2000 (low dose, n = 7) or 1:400 (high dose, n = 6). In the high-dose group, plasma atrial natriuretic factor concentration was significantly reduced by 65 +/- 14 pg/ml from basal levels of 165 +/- 12 pg/ml within 10 minutes and remained reduced for the 90-minute period after the injection. Fetal arterial pressure acutely and transiently decreased, but at 50 minutes arterial pressure increased and was elevated for the remainder of the experiment. Urine flow and urinary excretion rates of sodium, potassium, and chloride were reduced within 10 minutes after the injection. Urine flow rate was suppressed for as long as plasma atrial natriuretic factor concentrations were reduced. Fetuses in the low-dose and control groups showed no significant change in cardiovascular or renal function. In response to atrial natriuretic factor antiserum injection, plasma angiotensin II concentrations were increased, whereas plasma arginine vasopressin concentrations were unchanged. These results suggest that endogenous atrial natriuretic factor is involved in the maintenance of arterial pressure and urinary excretion in the ovine fetus.