Effects of cadralazine on systemic blood pressure, renal function and plasma renin activity in anesthetized dogs

Renal effects of ethyl 6-[ethyl(2-hydroxypropyl)amino]-3-pyridazinecarbazate (cadralazine), a newly synthesized vasodilator with a pyridazine ring, were studied in anesthetized dogs. 30 min after intravenous (i.v.) injection of cadralazine in a dose of 1 mg/kg diastolic blood pressure (DBP) decreased from the control value of 115 +/- 4 mmHg to 108 +/- 3 mmHg. The decrease continued, being accompanied by an increase in heart rate, throughout the experimental period of 5 h. Renal vascular resistance was decreased significantly, while glomerular filtration rate and urine volume remained unchanged. Urinary excretions of sodium and potassium were increased about 1.5 to 2 times as compared to pre-injection control values. Hypotension and natriuresis were followed by increased plasma renin activity in the artery or renal vein. On the other hand, i.v. injection of hydralazine (0.3 mg/kg) promptly decreased DBP and urinary sodium excretion, 15 min after administration, with blood pressure tending to revert to the control value. These results indicate that cadralazine has hypotensive and renal vasodilating actions, characterized by a slow onset and long duration, when compared with hydralazine.