Influence of heart rate on the effects of prenalterol on regional myocardial blood flow and function during coronary stenosis in dogs.
The effects of prenalterol, a selective beta 1-adrenoceptor agonist with potent cardiac positive inotropic properties have been investigated on regional myocardial blood flow (RMBF) (microspheres) and contractile function (ultrasonic crystals) during partial circumflex coronary artery stenosis in 8 open-chest anaesthetized dogs. Prenalterol was investigated at two intravenous doses: 5 micrograms kg-1, which increased myocardial contractility (dP/dt max: +29%) more than heart rate (+12%, up to 150 beats min-1) and 20 micrograms kg-1 which induced almost similar increases in contractility (+35%) and heart rate (+31% up to 175 beats min-1). The induced modifications of regional flow and function were then compared to those produced in another series of 6 dogs by atrial pacing at 150 and 175 beats min-1 respectively. Prenalterol significantly increased RMBF and segment length (SL)-shortening in a dose-dependent manner in the nonischaemic zone. In the ischaemic zone, RMBF was maintained and SL-shortening increased with prenalterol, 5 micrograms kg-1 whereas both RMBF and contractile function were severely decreased with prenalterol, 20 micrograms kg-1. Atrial pacing had almost no effect on RMBF and SL-shortening in the nonischaemic zone. In the ischaemic zone, atrial pacing rate-dependently decreased both RMBF and SL-shortening. Thus, a significant increase in contractility, associated with little tachycardia (prenalterol, 5 micrograms kg-1), induces beneficial effects on RMBF and function in both the nonischaemic and ischaemic myocardium. In contrast, a strong tachycardia, whether accompanied by positive inotropic effects (prenalterol, 20 gig kg-') or not (atrial pacing at 175 beats min-1) induces deleterious effects on RMBF and cardiac function in the ischaemic myocardium.
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002302:Cardiac Output / Q000187:drug effects; D002304:Cardiac Pacing, Artificial; D003326:Coronary Circulation / Q000187:drug effects*; D003327:Coronary Disease / Q000503:physiopathology*; D004285:Dogs; D005260:Female; D006339:Heart Rate; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D011217:Practolol / Q000031:analogs & derivatives* / Q000494:pharmacology; D011294:Prenalterol; D013997:Time Factors
D000318:Adrenergic beta-Agonists; D011294:Prenalterol; D011217:Practolol