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.


METHODS
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.


METHODS
Primary experimental.


METHODS
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).


METHODS
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).


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.
Rinaldi
G
G
Centro de Investigaciones Cardiovasculares, La Plata, Argentina.
Cingolani
H
H
D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D003243:Consciousness; D006973:Hypertension / Q000503:physiopathology; D008297:Male; D015737:Nisoldipine / Q000494:pharmacology; D009568:Nitrendipine / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D014700:Verapamil / Q000494:pharmacology
D000959:Antihypertensive Agents; D002121:Calcium Channel Blockers; D009599:Nitroprusside; D015737:Nisoldipine; D009568:Nitrendipine; D014700:Verapamil