Protection of the immature myocardium during ischemic arrest: dose dependent effects of glucose and mannitol when added to St Thomas' cardioplegic solution.

It has been suggested that immature hearts are less well protected by conventional cardioplegic solutions than are adult hearts. In an attempt to develop an improved cardioplegic solution for use in the immature ischemic heart the authors investigated whether the addition of various concentrations of glucose or mannitol to St Thomas' Hospital cardioplegic solution can improve its protective ability. Hearts from immature (three- to five-day-old) rats were perfused as Langendorff preparations with an indwelling left ventricular balloon. Contractile function (left ventricular developed pressure, maximum rate of development of pressure, heart rate, rate-pressure product and coronary flow) was recorded before and after a period of normothermic global ischemia with preischemic infusion (2 mins) of St Thomas' Hospital cardioplegic solution. In preliminary experiments the post ischemic recovery of contractile function was related to the duration of ischemia. With 60, 75, 90 and 120 mins of ischemia the post ischemic recovery of developed pressure was 47.6 +/- 3.9%, 17.4 +/- 5.5%, 15.0 +/- 5.4% and 13.8 +/- 4.8%, respectively, of its preischemic control. Comparable results were obtained with the other indices of cardiac function. The effect on the post ischemic recovery of function and tissue water content of the addition of mannitol or glucose (10, 20, 40, 60 or 80 mmol/L) to the cardioplegic solution was examined after 60 mins of ischemia. The mannitol groups tended to show consistently better recoveries at all concentrations studied but the improvement was small and rarely achieved a degree of statistical significance. In contrast glucose gave a U-shaped dose response profile with a significant deleterious effect at 10, 20 and 40 mmol/L.(ABSTRACT TRUNCATED AT 250 WORDS)