Evidence that a coronary alpha-adrenergic tone limits myocardial blood flow and oxygenation in acute hemorrhagic hypotension.
In 17 anesthetized dogs, left coronary blood flow (LCBF), left ventricular oxygen extraction [(a-v)O2], and myocardial oxygen consumption (MVO2) were monitored. Coronary perfusion pressure (CPP) was varied over a wide range by hemorrhage, and the effects of alpha-adrenergic blockade elicited by intracoronary phenoxybenzamine were assessed. During normotension (CPP greater than 80 mm Hg), blockade increased LCBF by 31 +/- 6 (SEM) %, but (a-v)O2 was substantially decreased so that MVO2 was increased by only 13 +/- 3%. At lower levels of CPP, the absolute increase in LCBF caused by blockade was similar to that during normotension, but because of the reduced preblockade LCBF, the percentage increase was greater. Thus, at a CPP of 50-80 mm Hg, LCBF increased by 41 +/- 15%, and at CPP less than 50 mm Hg, LCBF increased by 47 +/- 11% (P less than 0.05 compared to percentage of change during normotension). Furthermore, during hypotension the increase in LCBF after blockade was not accompanied by a large decrease in (a-v)O2. Consequently, in severe hypotension (CCP less than 50 mm Hg), both the absolute increase and the percentage increase in MVO2 was significantly greater than during normotension. These data suggest that during hypotension, especially severe hypotension, an alpha-adrenergic tone in the coronary circulation limits coronary flow and myocardial oxygenation.
D000818:Animals; D003326:Coronary Circulation; D003331:Coronary Vessels / Q000294:innervation*; D004285:Dogs; D005260:Female; D007022:Hypotension / Q000503:physiopathology*; D008297:Male; D009206:Myocardium / Q000378:metabolism; D010101:Oxygen Consumption; D010643:Phenoxybenzamine / Q000494:pharmacology; D012771:Shock, Hemorrhagic / Q000503:physiopathology*
D010643:Phenoxybenzamine