Influence of initial reperfusion pressure after hypothermic cardioplegic ischemia on endothelial modulation of coronary tone in neonatal lambs. Impaired coronary vasodilator response to acetylcholine.

To examine the effect of initial coronary reperfusion pressure on endothelial function, we subjected 16 isolated perfused neonatal lamb hearts to 2 hours of ischemia with potassium cardioplegic solution followed by reperfusion for 1 hour. Before ischemia both acetylcholine, an endothelium-dependent vasodilator, and nitroglycerin, and endothelium-independent vasodilator, caused coronary vasodilation. After ischemia the response to acetylcholine was impaired in the eight hearts with high initial reperfusion pressure (60 mm Hg) but was intact in the eight hearts with low initial reperfusion pressure (20 mm Hg for 10 minutes, 40 mm Hg for 10 minutes, and then 60 mm Hg thereafter). The response to nitroglycerin, however, remained intact regardless of initial reperfusion pressure. Recovery of resting coronary flow and myocardial oxygen consumption was lower in the group with high pressure reperfusion than in the group with low pressure reperfusion. On reperfusion a transient burst of coronary flow was exhibited by the hearts reperfused at high pressure. These results suggest that high initial reperfusion pressure impairs the endothelial modulation of coronary tone; this may be related to the effects on the coronary vasculature of the "burst" of coronary flow associated with high intravascular pressure.