Synergism of atenolol and amlodipine on lowering and stabilizing blood pressure in spontaneously hypertensive rats

This study was designed to investigate the possible synergism of atenolol and amlodipine on lowering and stabilizing blood pressure (BP) in spontaneously hypertensive rats. Sixty-four spontaneously hypertensive rats were randomly divided into eight groups. They were given 0.8% carboxymethylcellulose sodium (control), atenolol (10 mg/kg), amlodipine (0.5, 1 and 2 mg/kg) and the combinations of atenolol and amlodipine (10 + 0.5, 10 + 1 and 10 + 2 mg/kg), respectively. The drugs were given via a catheter of gastric fistula. BP was recorded for 25 h from 1 h before drug administration to 24 h after administration, in conscious, freely moving rats. It was found that combination of atenolol and amlodipine significantly decreased BP and systolic BP variability. From probability sum analysis it was found that the combination of atenolol and amlodipine, in a proportion as 10 : 1, was the best one (q = 1.54). In conclusion, the present work clearly demonstrated that there is a synergistic effect between atenolol and amlodipine in lowering and stabilizing the BP. The synergistic effect is highest when the dose proportion of the two drugs is 10 : 1.