AJP - Heart and Circulatory Physiology, Vol 251, Issue 3 656-H663, Copyright © 1986 by American Physiological Society
Effects of calcium entry blockade on left ventricular dynamics in exercising dogs
R. A. Walsh, F. X. Cleary and R. A. O'Rourke
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)
