Renal function studies with cadralazine in conscious dogs: a comparison with hydralazine

The effect of the antihypertensive vasodilator, cadralazine, on renal function in the conscious dog was compared to that of hydralazine using inulin and para-aminohippurate clearances. Both drugs were administered as intravenous bolus, at the dose of 1 mg/kg. As expected, hydralazine rapidly decreased mean blood pressure (from 110 to 89 mmHg), significantly increased heart rate (from 109 to 190 beats/min), markedly decreased urine volume (from 0.90 to 0.47 ml/min) and sodium excretion (from 101 to 45 microEq/min), and increased potassium excretion (from 28 to 53 microEq/min). Cadralazine displayed a similar activity on blood pressure and on heart rate, but differently from hydralazine, these effects appeared more slowly and were not accompanied by sodium and water retention. Hydralazine, but not cadralazine, caused a quick and transient decrease in glomerular filtration rate (from 55 to 40 ml/min), whereas both compounds increased renal plasma flow and reduced renal vascular resistance, renal extraction of para-aminohippurate and filtration fraction. Moreover, cadralazine increased plasma renin activity to a lesser extent than hydralazine, and this could explain the different effect on water and sodium excretion after acute administration of the two drugs.