Abstract

The direct effects of nifedipine (NF) on the heart, in an acute stenosis model, were separated from its peripheral effects by comparing the actions of each after intracoronary (i.c.) or systemic (i.v.) administration in the anesthetized dog. Myocardial blood flow and myocardial contractility [percent segment shortening (% SS)] were measured with radioactive microspheres and piezoelectric crystals in a normal and partially ischemic region, respectively. A stenosis was placed on the left anterior descending coronary artery which abolished autoregulation and reduced diastolic perfusion pressure to 20 to 25 mm Hg. Intravenous NF (0.5-1.0 microgram/kg/min) reduced mean arterial pressure (104 +/- 4 to 94 +/- 5 mm Hg) and distal coronary perfusion pressure (37 +/- 2 to 34 +/- 1 mm Hg). Transmural blood flow to the normal region was significantly increased (1.04 +/- 0.12 to 1.44 +/- 0.19 ml/min/g). Although subendocardial blood flow was not altered, subepicardial blood flow to the ischemic region was decreased (0.86 +/- 0.12 to 0.72 +/- 0.14 ml/min/g) after i.v. nifedipine. Despite the small decrease in subepicardial perfusion, % SS in the ischemic region was increased (3.0 +/- 2.6 to 7.4 +/- 2.3%, 147% increase). In contrast, i.c. NF (10 micrograms) had no effect on hemodynamics or myocardial blood flow to the normal or ischemic region. Myocardial contractility to the ischemic region was depressed [7.4 +/- 1.5 to (-)-1.1 +/- 2.6%, 115% decrease]. These data suggest that alterations in myocardial blood flow do not necessarily correlate with changes in myocardial contractility after NF administration.(ABSTRACT TRUNCATED AT 250 WORDS)