Heart & Cardiac Muscle

Abstract

Glutamine, present either throughout or only during reperfusion after short-term (20 min) normothermic low flow ischaemia, ameliorates post-ischaemic cardiac dysfunction (Khogali et al. 1998). We have now investigated the effects of glutamine on recovery of cardiac function after prolonged (75 min) cold (20 QC) cardioplegic arrest with St Thomas's Solution. Hearts (n = 16) were perfused at constant pre-and after-loads of 15 and 85 cmH 2 0, respectively, equilibrated for 20 min and then arrested by retrograde infusion of cardioplegia for 3 min before being surrounded with cardioplegic solution for another 72 min (with 2 min multidose infusion at 20, 40 and 60 min) followed by reperfusion. After 20 min of equilibration without glutamine, aortic output, coronary flow and cardiac output were 39'5 ± 1'7 (mean ± S.E.M.), 23'7 ± 1'6 and 63'0 ± 2'0 ml min -r, respectively. The heart rate was 225 ± 10 beats min -1 and th(j peak systolic aortic pressure was 96'8 ± 1'4 mmHg.In the absence or presence of glutamine in cardioplegic solution (up to 20 mM) and reperfusion solution (up to 10 mM), prolonged (75 min) cardioplegic arrest caused a significant (each P < 0'05, repeated measures ANOV A) diminution of cardiac output (Fig. 1). However, hearts treated with glutamine at 10 mM during cardioplegia and reperfusion manifested a doubling of their post-cardioplegic cardiac output compared with untreated hearts (P < 0'05); those treated with 20 mM glutamine during cardioplegia (1 mM during reperfusion) did not (Fig. 1). The myocardial lactate concentration increased significantly (P < 0'05, oneway ANOVA and Student-Newman-Keuls test) from 0'9 ± 0'1 (n = 5) to 2'6 ± 0'7 ,umol g -1 in untreated hearts, but not in those treated with 10 mM glutamine during cardioplegia and reperfusion (0'9 ± 0'05). The myocardial ATP / ADP ratio decreased significantly (each P < 0'05) from 6'0 + 0'5 in both untreated hearts (3'0 ± 0'4) and those treated with glutamine at 10 mM during cardioplegia and reperfusion (3'8 ± 0'4); however, PCr/Cr ratio returned to normal (0'5 ± 0'04) in both groups (0'5 ± 0'07 and 0'7 ± 0'1, respectively). We conclude that glutamine present at supraphysiological concentrations during reperfusion after prolonged cardioplegic arrest improves the post-cardioplegic cardiac output; nevertheless, glutamine added during cardioplegia provides no benefit.Journal of Physiology (1998) Intermittent antegrade warm blood hyperkalaemic cardioplegia (lA WBC) was recently proposed as an improved method of myocardial protection when compared with intermittent antegrade cold blood cardioplegia during open heart surgery (Calafiore et al. 1995). Unlike crystalloid cardioplegia which contains high magnesium, lA WBC utilizes potassium as the only additive. However, there are strong theoretical reasons to support the addition of magnesium to this cardioprotective strategy. Therefore the influence of the addition of magnesium (5 mM) on myocardial protection with intermittent antegrade warm blood hyperkalaemic cardioplegia (lA WBC + Mg) in pati...