Effect of furosemide on plasma atrial natriuretic peptide and aldosterone concentrations and renin activity in running horses.

Effects of furosemide administration on exertion-induced changes in plasma renin activity and plasma concentrations of atrial natriuretic peptide and aldosterone in horses during sustained submaximal exertion were examined. Furosemide (1 mg/kg of body weight) or heparinized saline solution was administered IV to each of 6 mares not conditioned to exercise, either 4 hours or 2 minutes before 60 minutes of sustained submaximal running on a treadmill. Horses ran at a speed that induced heart rate approximately 65% of maximal after saline treatment. After 15 minutes of running, furosemide suppressed the exertion-induced increase in plasma concentrations of atrial natriuretic peptide (mean [95% confidence interval] values of 63.9 [9.9 to 421] pg/ml vs 100 [15.4 to 652] pg/ml after furosemide or saline treatment, respectively), and enhanced the response of plasma renin activity to exertion (18.6 [5.7 to 60.4] ng/ml/h vs 6.0 [1.8 to 19.4] ng/ml/h, respectively). An effect of furosemide on the exertion-induced increase in plasma aldosterone concentration was not detected.