Comparative effects of verapamil, diltiazem and nifedipine on aortic compliance in anesthetized dogs.

We tested the ability of verapamil (V), diltiazem (DTZ) and nifedipine (NIF) to alter aortic compliance upon i.v. administration in anesthetized dogs. Sonomicrometry was used to measure aortic systolic (SD) and diastolic (DD) diameters. Aortic distention (AD) was calculated from SD-DD. Aortic compliance was computed from the ratio of AD to arterial pulse pressure. One aortic compliance unit (ACU) is defined as 10(-3) mm/mmHg. V (0.1-3.0 mg/kg) reduced blood pressure, SD and DD dose-dependently. DD was more affected than SD and AD rose significantly. Since pulse pressure was not significantly altered, V induced a dose-related increase in aortic compliance. The 3.0 mg/kg dose increased aortic compliance by 10.3 +/- 1.5 ACU from a basal value of 4.7 +/- 0.5 ACU. DTZ (0.1-3.0 mg/kg) produced effects on blood pressure, aortic dimensions and aortic compliance similar to those seen with V. Infusion of NIF (3.2-32 micrograms/kg/min) exhibited a similar profile, i.e., reduced blood pressure, SD, DD and increased AD and aortic compliance. NIF, however was limited in its ability to increase aortic compliance, i.e., increases of 3.2 +/- 1.0 or 3.8 +/- 0.6 from basal values of 4.9 +/- 1.0 ACU were obtained with 10 and 32 micrograms/kg/min NIF, respectively. Although these 3 prototype calcium entry blockers share a common profile of action, V and DTZ appear to have a greater efficacy on aortic compliance than NIF.