Interactions of diuretics with the renal kallikrein-kinin and prostaglandin systems.

The renal kallikrein-kinin system may participate in the diuretic, natriuretic and antihypertensive effect of diuretics. This possibility was investigated by studying the influence of hydrochlorothiazide on blood pressure and urinary kallikrein excretion in patients with essential hypertension. Furthermore, the effect of kallikrein-blockade and prostaglandin-synthesis inhibition on the acute furosemide-induced changes of diuresis, natriuresis, GFR and renal plasma flow were studied in normotensive subjects. Thiazide treatment normalized the reduced kallikrein excretion of the hypertensive patients. The fall in mean arterial blood pressure was significantly correlated with the increase in urinary kallikrein excretion. In the normotensive subjects aprotinin-induced kallikrein inhibition failed to alter the acute response to furosemide, whereas indomethacin attenuated the diuretic and natriuretic effect of furosemide. The combination of indomethacin and aprotinin had a greater suppressive effect on plasma renin activity than indomethacin alone, suggesting a participation of kallikrein in renin release. An increase in the activity of the renal kallikrein-kinin system may contribute to the long-term antihypertensive effect of thiazide diuretics but it does not seem to be involved in the acute renal responses to furosemide.