Relationship between baseline blood pressure and blood pressure decrease after calcium channel blockers in conscious rats.

OBJECTIVE

To determine whether vasodilators produce a fall in mean blood pressure (MBP) that is directly proportional to baseline MBP.

DESIGN

The effects on blood pressure of three calcium channel blockers, nitrendipine, nisoldipine and verapamil, were compared with sodium nitroprusside, a drug acting through a different mechanism. The drugs were infused in conscious, unrestrained rats and their effect on MBP was measured.

SETTING

Primary experimental.

ANIMALS

Animals were divided into three groups according to their baseline MBP: high (greater than 119 mmHg), moderate (91 to 119 mmHg) and normal (less than 91 mmHg).

INTERVENTIONS

Five successive infusion rates for each drug were tested in each animal. MBP readings were taken at the end of each infusion period (usually 10 mins).

MAIN RESULTS

At the maximal dose infused, nitrendipine (0.57 mg/kg.min) lowered MBP 13 +/- 6 mmHg in the low MBP rats, 51 +/- 4 mmHg in the rats with moderate MBP and 83 +/- 8 mmHg in the rats with high MBP (P < 0.05 within groups). Similar results (ie, the greater the baseline MBP, the greater the fall in MBP) were obtained with nisoldipine and verapamil. In the same groups, sodium nitroprusside (0.096 mg/kg.min) produced a fall of 52 +/- 3 mmHg, 56 +/- 5 mmHg and 54 +/- 13 mmHg, respectively (not significant).

CONCLUSIONS

Nitrendipine, nisoldipine and verapamil behave as antihypertensives since their effect increased as a function of the initial MBP, while sodium nitroprusside showed no effect related to baseline MBP.