INTRARENAL STIMULATION OF RENIN SECRETION BY FRUSEMIDE IN THE ISOLATED KIDNEY OF THE RAT

1 Intrarenal infusion of frusemide markedly stimulated renin secretion in the isolated perfused kidney of the rat. 2 Renin values increased from 24 ± 6 to 195 ± 34 units of secretion rate (renin concentration (nmol angiotensin I/h per litre) × flow rate (ml/min)) following administration of frusemide for 8 min, compared with corresponding control values of 13 ±2 (P >0.05) and 47 ±18 (P < 0.001). This stimulatory effect was also observed when urine flow was interrupted by ligation of the ureters. 3 The changes in renal perfusion pressure and perfusate flow rate were not significantly different from the control values. 4 These findings indicate the existence of an intrarenal site of action for frusemide on renin secretion. 5 Since frusemide did not appear to alter perfusion pressure or flow rate, and was effective when urine flow was abolished, a dominant role for a vascular or macula densa receptor mechanism seems unlikely. A direct effect of frusemide on the renin secreting cell is therefore suggested.