The goal of this study was to assess the effect of multi-dose St Thomas car
dioplegia on intracellular sodium homeostasis in a rat heart model. A new m
agnetic resonance method was applied which enable us to detect intracellula
r Na changes without chemical shift reagents. Three groups of isolated rat
hearts were subjected to 51 min of ischemia and 51 min of reperfusion at 37
degrees C: Group 1-three infusions of St Thomas cardioplegia every 17 min
for 2 min (n = 7); Group 2-single-dose infusion of cardioplegia at the begi
nning of stop-flow ischemia (n = 8); and Group 3-clamp ischemia (n = 3) wit
hout cardioplegia administration. Performance of the heart was assessed by
rate-pressure product relative to the pre-ischemic level (RPP). An NMR meth
od was applied which continuously detects the Na-i concentration in the hea
rt, using the ability of bound sodium to exhibit triple-quantum transitions
and the growth of the corresponding signal when sodium ions pass from extr
acellular to intracellular space. Clamp ischemia without cardioplegia and 5
0 min of reperfusion left the heart dysfunctional. with Na-i growth from th
e pre-ischemic level of 13.9 +/- 1.2 mM to 34.9 +/- 1.3 mM and 73,9 +/- 1.9
mM at the end of ischemia and reperfusion. respectively. During single-dos
e cardioplegia the corresponding values for Na-i were 30.2 +/- 1 mM and 48.
5 +/- 1.7 mM (RPP = 29%). Multiple infusions of cardioplegic solution resul
ted in a remarkable preservation of the heart's intracellular Na concentrat
ion with a non-significant increase in Na-i during ischemia and only 16.7 /- 1 mM, (P = 0.01), after subsequent reperfusion (RPP = 85%). The time cou
rse of Na-i changes in the rat heart model demonstrates a prominent potenti
al of multi-dose St Thomas' cardioplegia in preserving intracellular sodium
homeostasis at 37 degrees C. The growth of Na-i concentration during ische
mia, as an indicator of the viability of the myocytes, can reperfusion. hav
e a prognostic value for the heart's performance during (C) 1999 Academic P
ress.