Circulating concentrations and physiologic role of atrial natriuretic peptide during endotoxic shock in the rat

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Abstract
To determine if there are changes in circulating concentrations of endogenous atrial natriuretic peptide and the physiologic role of this peptide in endotoxic shock. A prospective, randomized, controlled animal trial. University research laboratory. Anesthetized male Wistar rats, weighing 250 to 350 g. Six rats received 1.5 mg/kg body weight of lipopolysaccharide alone. Five rats received 1.5 mg/kg of lipopolysaccharide and 200 micro Liter/100 g body weight of rabbit anti-atrial natriuretic peptide serum. Another five rats received 1.5 mg/kg of lipopolysaccharide and normal rabbit serum in the same volume as the antiserum. Plasma concentrations of atrial natriuretic peptide, arginine vasopressin, and aldosterone were measured, and changes in hemodynamic parameters and renal function were monitored in rats with endotoxic shock after catheterization of the right jugular vein. Urine volume, urine sodium excretion, urinary potassium excretion, and urine 3 prime, 5 prime-cyclic guanosine monophosphate (cGMP) excretion were measured at 12-hr intervals. The plasma atrial natriuretic peptide concentration was slightly but significantly lower 30 mins after the lipopolysaccharide injection (114.8 plus minus 9.0 pg/mL at 0 hr, 75.6 plus minus 6.2 pg/mL at 30 mins, p less than .01) and then began to increase, peaking at 6 hrs (752.8 plus minus 104.5 pg/mL, p less than .01 vs. 0 time) and remaining at higher concentrations than before the preinjection value, up to 24 hrs. In contrast, acute spike-like increases of arginine vasopressin and aldosterone concentrations were observed 30 mins after the lipopolysaccharide injection, preceding the increase of the plasma atrial natriuretic peptide concentration. Measurements of urine volume and urine sodium excretion showed oliguria during the initial 12 hrs after the lipopolysaccharide injection, followed by diuresis and natriuresis during the subsequent 12 hrs. In addition, injection with anti-atrial natriuretic peptide serum in the diuretic phase 12 hrs after the lipopolysaccharide injection significantly inhibited the diuresis, natriuresis, and urine cGMP excretion in this model. Furthermore, the plasma aldosterone concentration 24 hrs after the lipopolysaccharide injection was significantly increased by the administration of the antisera. These findings suggest that endogenous atrial natriuretic peptide increases in the acute phase of endotoxic shock and plays an important role in water and electrolyte balance by regulating diuresis.