Effects of indomethacin on furosemide induced renal prostaglandin synthesis and action in man.

We had previously shown that the early increment in plasma renin activity occurring within ten minutes of intravenous furosemide is accompanied by an increase in urine 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) the hydrolysis product of prostacyclin. Renal prostacyclin and thromboxane A2 synthesis are apparently limited to the cortex. To assess whether indomethacin would inhibit renal cortical eicosanoid synthesis and whether such reduction correlated with reduced early renin release, we assessed responses to intravenous furosemide (0.5 mg/kg) before and after indomethacin (150 mg/day for seven days) in ten normal male volunteers. Indomethacin did not change blood pressure but increased weight slightly (79.7 +/- 2.5 kg to 80.4 +/- 2.4 kg, p less than 0.05). Serum thromboxane B2 (TXB2), a measure of platelet thromboxane A2 production, was profoundly depressed (142 +/- 29 ng/ml to 4.8 +/- 1.6 ng/ml, p less than 0.001). Neither diuresis nor natriuresis were changed by indomethacin but potassium excretion was reduced (33 +/- 4 mmol/4 hr to 27 +/- 3 mmol/4 hr, p less than 0.05). Basal as well as furosemide stimulated plasma renin activity (at 10, 30 and 240 minutes) was reduced, as well as the transient increase in excretion rates of 6-keto-PGF1 alpha and TXB2. We conclude that the reduction in furosemide stimulated renin release by indomethacin is due to renal cyclo-oxygenase inhibition which is reflected in decreased excretion rates of hydrolysis products of renal eicosanoids.