Plasma renin activity and renal sodium and water excretion following infusion of arachidonic acid in rats

Plasma renin activity (PRA) and urinary sodium and water excretion were measured following infusion of the prostaglandin (PG) precursor arachiodonic acid (C20 : 4) in normal hydrated rats (saline i.v.: 0.5 ml/hr/100 g body weight) and in rats with moderate volume expansion (saline i.v.: 1.5 ml/hr/100 g body weight). Nonhypotensive doses of C20 : 4 (40–70 μg/min/100 g b.w.) increased PRA in both normal and volume-expanded rats (p < 0.05, and p < 0.025, respectively). In volume-expanded rats, C20 : 4 was followed by reduced urine volume (p < 0.01) and sodium excretion (p < 0.001) in comparison to volume-expanded control rats, whereas in normal hydrated rats these parameters remained unchanged after C20 : 4. The present results indicate that the C20 : 4-stimulated PG-synthetase system can increase PRA independently of the extracellular fluid volume. Futhermore, these results suggest a complex interrelationship between PG-synthetase action, activation of the renal renin—angiotensin system and urinary water and sodium excretion.