Conscious rats, with implanted carotid arterial cannulae, received a saline infusion (5.8 ml./hr) via a tail vein for a 6 hr period. The urinary excretion of water, sodium, potassium, urea and the osmolal output were monitored, together with the systemic blood pressure. Glomerular filtration rate (inulin clearance) and effective renal plasma flow (p-aminohippurate clearance) were also measured. Four hours after the start of the infusion, indomethacin (10 mg/kg body weight) in buffered saline, or buffered saline alone, was administered via the tail vein. 2. Following indomethacin administration, urine flow, sodium output and osmolal output were markedly reduced (P less than 0.01). However, there were no measurable changes in the systemic blood pressure, glomerular filtration rate, or effective renal plasma flow. 3. It is concluded that the changes in urinary excretion observed after indomethacin are not dependent on changes in effective renal plasma flow or glomerular filtration, and it is suggested that indomethacin inhibits the synthesis of endogenous prostaglandins which directly influence renal tubular function.
