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Ann Thorac Surg 1994;57:682-688
© 1994 The Society of Thoracic Surgeons
Cardiovascular Research, The Hospital for Sick Children, Toronto, Ontario, Canada
Accepted for publication June 9, 1993.
* Address reprint requests to Dr He, Cardiothoracic Surgery Assuciates's of North Texas at Medical City Dallas Hospital, C-740, 7777 Forest Lane, Dallas, TX 75230.
Results of previous studies have suggested that high K+ concentrations in cardioplegic solutions may be detrimental to coronary endothelium in perfused hearts, as determined from changes in the coronary flow rate, but the direct functional changes in endothelium secondary to hyperkalemia have not been fully studied. To determine the effect of the K+ concentration in a physiologic solution (Krebs') and in St. Thomas' cardioplegic solution, and the effect of exposure time on endothelium and smooth muscle, porcine coronary artery tings were set up in organ baths under a physiologic pressure. The effect of exposure to Krebs' solution containing 5.9 or 50 mmol/L K+ or to St. Thomas' solution containing 16 or 50 mmol/L K+, for either 2 hours (group I) or 4 hours (group II), was examined. The solutions were continuously aerated with 95% oxygen and 5% carbon dioxide to exclude the effects of ischemia and hypoxia. The rings were then washed and contracted with K+ (25 mmol/L). The ability to release endothelium-derived relaxing factor IEDRF) in response to an EDRF stimulus (substance P) was used as an index of endothelial function. Smooth muscle function was evaluated in terms of the K+-induced contraction force and the relaxation induced with glyceryl trinitrate, in addition to the maximal substance P-induced relaxation. The maximal relaxation induced by substance P did not decrease by incubation with 50 mmol/L K+ in any group (p > 0.05). However, in group II rings incubated for 4 hours in Krebs' solution containing 50 mmol/L K+, the contraction force to 25 mmol/L K+ (11.0 ± 1.4 g) was significantly less than that in the rings incubated with Krebs' solution (17.5 ± 1.2 g; p < 0.05), There was no difference in the maximal relaxation induced by glyceryl trinitrate (p > 0.05). While the rings were incubated, St. Thomas' solution brought about slight relaxation of the rings, and no changes in either endothelium or smooth muscle function were seen even with an elevated K+ level of 50 mmol/L. These results suggest that (1) the endothelium and smooth muscle of the porcine coronary artery are relatively resistant to hyperkalemia; (2) coronary endothelium may be more tolerant to hyperkalemia than is smooth muscle; and (3) coronary artery smooth muscle damage caused by hyperkalemia during prolonged (4 hours) incubation may be prevented by cardioplegia.
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