text: Treatments with losartan or enalapril are equally sensitive to deterioration in renal function from cyclooxygenase inhibition.
  The beneficial effects of angiotensin converting enzyme (ACE)-inhibitors are in part mediated through the inhibition of the degradation of the vasodilator bradykinin. The bradykinin effect is counteracted by cyclooxygenase-inhibitors. Angiotensin receptor blockers (ARBs) do not affect bradykinin. To test the hypothesis that renal counteraction from a cyclooxygenase-inhibitor, diclofenac, is different in subjects treated with an ACE-inhibitor, enalapril compared with an ARB, losartan. Twelve elderly, healthy, slightly over-hydrated subjects received diclofenac orally after pre-treatment with a diuretic, bendroflumethiazide, and enalapril or bendroflumethiazide and losartan, in a double-blind cross-over fashion, with a wash-out period of at least 1 week. Diclofenac reduced GFR significantly from 81(64-98) ml/min at first observations after dose for enalapril to 29(16-42) and from 76(64-88) after losartan to 35(24-46). There was no significant difference between enalapril and losartan in GFR. Diclofenac induced decreases in urine flow, excretion rates and clearances of sodium, osmolality clearance and free water clearance, irrespective of treatment with enalapril or losartan. However, serum potassium and handling of potassium were significantly lower after losartan-treatment. The negative renal effects of diclofenac administration in subjects with activation of the renin-angiotensin system and enalapril treatment are the same in subjects with activation of the renin-angiotensin system and losartan treatment.