Comparison of UW solution and St. Thomasʹ solution in the rat: Importance of potassium concentration

Background. University of Wisconsin solution (UW) is in limited clinical use for heart transplantation, but there are doubts about its efficacy and concerns about the effect of its high K+ concentration on endothelium. St. Thomasʹ solution with or without aspartate is widely used and is of proven efficacy. Methods. Using a modified (starch-free) variant of UW (MUW) we studied: (1) recovery of function with UW compared with aspartate-containing St. Thomasʹ solution; (2) effect of elevation of K+ in St. Thomasʹ solution to the level in UW; and (3) effect of reduction of K+ in UW and addition of Ca2+ or aspartate. Isolated rat hearts underwent 7 hours of arrest at 1°C using MUW with or without 20 mmol/L aspartate or using aspartate-containing St. Thomasʹ solution. Results. Functional recovery with MUW (51.8% ± 2.5%) was superior to that with aspartate-containing St. Thomasʹ solution (37.1% ± 4.3%; p < 0.01). Addition of aspartate to MUW had no effect. During 6 hours of arrest, lowering the K+ in MUW from 125 mmol/L to 20 mmol/L reduced functional recovery from 59.9% ± 4.2% to 42.3% ± 4.3% (p < 0.01). The addition of 1 mmol/L Ca2+ had no effect. Elevation of K+ in St. Thomasʹ solution produced more rapid arrest but no improvement in recovery. Conclusions. The protective effect of starch-free UW is greater (+13%) than that of aspartate-enriched St. Thomasʹ solution. Reduction of K+ in UW to lessen possible deleterious effects would decrease its protective effect by about 30% to a level comparable with that of St. Thomasʹ solution.