DIFFERING PROTECTION WITH ASPARTATE AND GLUTAMATE CARDIOPLEGIA IN THEISOLATED RAT-HEART

Aspartate and glutamate each have been shown to improve cardiac recove ry after hypoxia or ischemia under normothermic conditions, but whethe r their effects are additive acid to what extent they are modified by hypothermia has not been studied systematically. We set out to compare the individual and combined protective effects of aspartate and gluta mate during cardioplegic arrest under normothermic and hypothermic con ditions in the rat. Using isolated working rat hearts, functional and metabolic recovery was assessed after 0.5 hours of potassium arrest at 37 degrees C of 5 hours at 2 degrees C in control hearts (C) and in h earts in which 20 mmol/L glutamate (G), 20 mmol/L aspartate (A) or bot h (A + G) was added to the cardioplegic solution. Under normothermic c onditions, percentage recovery of prearrest work (mean +/- standard er ror of the mean) was as follows: C = 31.7 +/- 2.8, G = 34.8 +/- 0.2, A = 49.6 +/- 2.8, A + G = 53.7 +/- 2.3*. Under hypothermic conditions, the values were as follows: C = 40.4 +/- 4.0, G = 45.2 +/- 2.3, A = 5 9.4 +/- 1.8, A + G = 54.1 +/- 1.2* (*p < 0.01 versus C and G). Recove ry of postischemic high-energy phosphate content followed the same pat tern: A = A + G > G or C. Measurement of postischemic myocardial conte nt of amino acids showed that recovery of function and energy status c orrelated with maintenance of myocardial levels of aspartate (r = 0.9; p < 0.01) but not glutamate. We conclude that aspartate cardioplegia is protective against ischemia under normothermic and hypothermic cond itions due to its ability to augment postischemic myocardial aspartate levels.