[Comparison of negative chronotropic action of nitrendipine, nifedipine and verapamil on the isolated right atrium of normotensive and renovascular hypertensive rats].

PURPOSE

To study the negative chronotropic effects of nitrendipine, nifedipine and verapamil in isolated right atria from normotensive and renovascular hypertensive rats.

MATERIAL AND METHODS

Hypertension (medium arterial pressure, MAP = 154 +/- 4 mmHg) was induced by applying a silver clip to the left renal artery and right nephrectomy. Control rats (MAP = 109 +/- 2 mmHg) were submitted to right nephrectomy only. The animals were studied 2 weeks after surgery. Different preparations were used to obtain cumulative dose-response curves (0.01 microM to 100 microM) with each drug.

RESULTS

No difference in "in vitro" initial sinusal rate of control (243 +/- 7 bpm) and hypertensive (245 +/- 5 bpm) rats was observed. The negative chronotropic response produced by calcium channel blockers was similar in normotensive and hypertensive groups. 2 microM verapamil, 4 microM nitrendipine or 20 microM nifedipine was necessary to produce a 50% decrease of the initial sinusal rate.

CONCLUSION

Sensitivity of the sinusal pacemaker to calcium antagonists does not change in this model of hypertension. Moreover, the negative chronotropic effect of nitrendipine is stronger than nifedipine and weaker than verapamil.