DIFFERENTIAL-EFFECTS OF INTRAVENOUS VS INTRACORONARY NIFEDIPINE ON MYOCARDIAL SEGMENT FUNCTION IN ISCHEMIC CANINE HEARTS

  • 1 January 1984
    • journal article
    • research article
    • Vol. 228  (1) , 28-32
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. [intravenous]) 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 20-25 mm Hg. I.v. NF (0.5-1.0 .mu.g/kg per 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 per 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 per 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). I.c. NF (10 .mu.g) 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]. Alterations in myocardial blood flow apparently do not necessarily correlate with changes in myocardial contractility after NF administration. At doses which had no effect on contractility in the nonischemic myocardium, NF improved % SS in the ischemic area after i.v. administration, possibly due to its peripheral effects; however, it had a direct myocardial depressant effect when given i.c.