Effects of calcium entry blockade on left ventricular dynamics in exercising dogs.

Abstract

To study the previously undefined effects of calcium entry blockade on left ventricular (LV) function and coronary blood flow during dynamic exercise we gave intravenous equihypotensive infusions of nifedipine (10 +/- 4 SE micrograms X kg-1 X min-1), diltiazem (60 +/- 8 micrograms X kg-1 X min-1), and verapamil (52 +/- 7 micrograms X kg-1 X min-1) before and after intravenous propranolol (2 mg/kg) to chronically instrumented dogs at rest and while running on a treadmill at 4 and 10 km/h. Prior to beta-blockade, each agent significantly and equivalently (P = NS among drugs) reduced mean arterial pressure during exercise (-13% nifedipine, -8% diltiazem, -15% verapamil at 4 km/h, each P less than or equal to 0.01 vs. exercise alone) but did not significantly alter LV end-diastolic dimension (EDD), heart rate, or cardiac output compared with exercise alone. Only verapamil blunted the positive inotropic response to exercise (LV dP/dtmax decreased 20% at 4 km/h, P less than 0.01 vs. exercise alone). Coronary blood flow was significantly and equivalently increased at rest and during submaximal exercise with each calcium blocker, but this effect was largely offset by propranolol. During exercise after beta-blockade each agent produced significant additional reductions in mean arterial pressure and dP/dtmax at peak exercise but did not alter LVEDD or heart rate compared with results obtained with propranolol alone. Combined beta-blockade and verapamil uniquely diminished myocardial contractility to a greater extent at peak exercise than at rest (dP/dtmax 1,260 +/- 410 peak exercise vs. 1,775 +/- 431 mmHg/s rest, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)