Different antihypertensive effects of nifedipine in conscious experimental hypertensive and normotensive rats

Antihypertensive effects of nifedipine and hydralazine were investigated in normotensive rats, spontaneously hypertensive rats (SHR), DOCA-NaCl hypertensive rats and renal hypertensive rats all in a conscious state. The blood pressure fall after nifedipine 5 mg/kg p.o. was 22% of the initial value in normotensive rats, 49% in SHR, 53% in DOCA-NaCl hypertensive rats and 44% in renal hypertensive rats. Hydralazine in the same dose decreased the blood pressure by 40% in normotensive rats, 52% in SHR, 33% in DOCA-NaCl hypertensive rats and 54% in renal hypertensive rats. The selective action of nifedipine in hypertensive rats in contrast to normotensive rats seemed to be attributable to the different affinity for calcium ion of vascular smooth muscle of hypertensive rats as compared with that of normotensive rats. Also, the heart rate of hypertensive rats or normotensive rats was increased with nifedipine but less than with hydralazine.