Abstract 316: Effect of Different Substrates on Functional Performance and Kinase Activation During Reperfusion After Ischemia in Hearts from Obese Insulin Resistant Rats
Insulin resistance decreases glucose uptake, alters lipid metabolism and impairs PKB-dependent signaling in its target tissues. In view of the myocardial dependence on glycolysis during energy deficiency, insulin resistance may exacerbate the harmful effects of ischaemia. We hypothesize that obesity-induced insulin resistance affects functional recovery and activation of PKB, JNK, ERK and PTEN during early reperfusion.
Methods: Insulin resistance was induced by feeding rats a high calorie diet for 16 weeks. Hearts from diet rats (D) and age-matched controls (C) were subjected to (i) 15 min global ischaemia and different reperfusion times for Western blot and measurement of functional recovery, or (ii) 35 min regional ischaemia and 2 hours reperfusion for infarct size determination (IS) using tetrazolium. Substrates were glucose (G) (10mM) or glucose (10mM) plus fatty acid (FA) (1.2mM palmitate /3%BSA) (G+FA). N=4-8/group.
Results: Regardless of the substrate, functional recovery during reperfusion of hearts from D was higher than those of C (% recovery of total work: D+G/C+G, 69.1±3.4/50.7±4.5, D+G+FA/C+G+FA: 105.4±3.6/92.7±3.9), associated with a reduction in IS (D+G/C+G 29.7±2.8/43.5±2.5, p<0.05; D+G+FA/C+G+FA 26.7±3.2/36.6±4, p<0.05). When perfused with glucose hearts from D showed increased activation of PKB and JNK at different times during reperfusion (D+G/C+G: 10 min PKBs473, 1.41±0.11/1.00±0.06; JNKp54, 1.80±0.15/1.00±0.13; JNKp46, 1.59±0.11/1.00±0.08). Addition of FA caused further activation of the kinases (e.g. D+G+FA/D+G: 5 min ERKp44, 1.54±0.11/1.00±0.11, ERKp42, 1.46±0.13/1.00±0.07; 10 min ERKp44, 1.83±0.19/1.00±0.05, ERKp42, 1.27±0.10/1.00±0.05; 30 min PKBs473, 2.91±0.35/1.00±0.09) and inhibition of PTEN (1.79±0.11/1.00±0.10).
Conclusion: Contrary to expectations, hearts from D rats showed an increased tolerance to ischaemia/reperfusion (I/R) injury which was further improved by fatty acids in the perfusate. The pattern of PKB, JNK, ERK and PTEN phosphorylation during reperfusion is substrate dependent and significantly higher in hearts from D rats. With glucose as substrate activation of PKB and JNK during reperfusion was higher in hearts from D rats while FA further improved activation of ERK and PKB.
- © 2012 by American Heart Association, Inc.