Effects of nifedipine on renal responses to several diuretic agents in rats.

The influence of the dihydropyridine calcium antagonist nifedipine has been studied on the diuretic response to frusemide, acetazolamide and hydrochlorothiazide in water-loaded (25 mL kg-1) conscious rats. Oral administration of nifedipine (10 mg kg-1) markedly inhibited frusemide- and hydrochlorothiazide-induced diuresis as evidenced by a reduction in 5 h urine volume and urinary sodium and potassium elimination. However, it neither significantly enhanced nor limited urine and electrolyte excretion promoted by acetazolamide. Nifedipine, 5 and 10 mg kg-1 but not 1 mg kg-1, significantly (P less than 0.05) inhibited the diuretic response of hydrochlorothiazide. At doses which affect hydrochlorothiazide diuresis (5 and 10 mg kg-1), nifedipine was found to depress the mean arterial pressure by 32% in normotensive rats. These results are of interest in view of the often reported clinical side effect of nifedipine in promoting peripheral oedema in hypertensive patients and its use in combination with a thiazide or loop diuretic.