Effects of atrial extract on blood pressure and urinary excretion of electrolytes and prostaglandin E2 in rats.

The mechanism of natriuresis following administration of atrial extract is not fully understood. This study related the changes in urinary excretion of electrolytes induced by atrial or ventricular extract to those in urinary excretion of prostaglandin E2 (PGE2) in rats. Both atria were removed from Wistar rats and homogenized in a 1 N acetic acid solution. After centrifugation, the supernatant was lyophilized and then resolved in a 0.1 N acetic acid solution. The apical portions of heart ventricles were similarly prepared, and served as controls. One hundred microliter of the solution containing the extract of 10 mg of tissue were injected intravenously into assay rats, the carotid artery and the urinary bladder of which were cannulated to measure blood pressure and urinary output, respectively. Urinary PGE2 was determined by radioimmunoassay. The atrial extract rapidly lowered blood pressure without changing heart rate. This hypotensive effect was maintained for at least 30 minutes. When the urinary samples obtained before and 10 minutes after the injection of the atrial extract were compared, urinary volume and excretion of sodium (UNaV) and potassium (UKV) were increased by 8, 24 and 3-fold, respectively. Urinary excretion of PGE2 (UPGEV) was increased from 5.3 +/- 0.9 (SE) to 16.3 +/- 2.9 ng/kg/10 min (p less than 0.001). There was a significant positive correlation between UNaV and UPGEV in all the samples (r = 0.72, p less than 0.001), and between the changes in UNaV and those in UPGEV after administration of the atrial extract (r = 0.62, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)