A comparative study of the action of frusemide and methyclothiazide on renin release by rat kidney slices and the interaction with indomethacin.

1 The effects of frusemide (a diuretic acting on the loop of Henle) and methyclothiazide (a thiazide diuretic) on renin release were studied on rat kidney slices. 2 Frusemide at concentrations of 1.5 and 7.5 mmol/l produced significant increases in renin release but had no effect at 0.15 mmol/l. 3 Methyclothiazide in a similar concentration range did not increase renin release; instead, at the highest concentration used, methyclothiazide (3.5 mmol/l) inhibited renin release. 4 Indomethacin (25 mumol/l) did not inhibit the increase of renin induced by frusemide. 5 Our limited study in vitro is consistent with the findings of other workers who have shown in vivo, in the absence of systemic electrolyte depletion, that only "loop diuretics" increase renin secretion. Under our experimental conditions, it is suggested that frusemide exerts a direct action either upon the epithelioid cells or upon the macula densa since the renal prostaglandin system does not intervene.