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p38 mitogen-activated protein kinase (MAPK) and 5′-AMP-activated protein kinase (AMPK) are activated by metabolic stresses and are implicated in the regulation of glucose utilization and ischemia-reperfusion (IR) injury. This study tested the hypothesis that inhibition of p38 MAPK restores the cardioprotective effects of adenosine in stressed hearts by preventing activation of AMPK and the uncoupling of glycolysis from glucose oxidation. Working rat hearts were perfused with Krebs solution (1.2 min palmitate, II min [³H/14C]glucose, and 100 mU/I insulin). Hearts were stressed by transient antecedent IR (2 × to min 1/5 min R) before severe IR (30 min 1/30 min R). Hearts were treated with vehicle, p38 MAPK inhibitor (SB-202190, 10 µM), adenosine (500 µM), or their combination before severe IR. After severe IR, the phosphorylation (arbitrary density units) of p38 MAPK and AMPK, rates of glucose metabolism (µmol g · dry wt-1 · min-1), and recovery of left ventricular (LV) work (Joules) were similar in vehicle-, SB-202190- and adenosine-treated hearts. Treatment with SB-202190 + adenosine versus adenosine alone decreased p38 MAPK (0.03 ± 0.01, n = 3 vs. 0.48 ± 0.10, n = 3, P < 0.05) and AMPK (0.00 ± 0.00, n 3 vs. 0.26 ± 0.08, n = 3 P < 0.05) phosphorylation. This was accompanied by attenuated rates of glycolysis (1.51 ± 0.40, n = 7 vs. 3.95 ± 0.65, n = 7, P < 0.05) and H~ production (2.12 ± 0.76, n = 7 vs. 6.96 ± 1.48, n = 7, P < 0.05), and increased glycogen synthesis (1.91 ± 0.25, n = 6 vs. 0.27 ± 0.28, n = 6, P < 0.05) and improved recovery of LV work (0.81 ± 0.08, n = 7 vs. 0.30 ± 0.15, n = 8, P < 0.05). These data indicate that inhibition of p38 MAPK abolishes subsequent phosphorylation of AMPK and improves the coupling of glucose metabolism, thereby restoring adenosine-induced cardioprotection. [ABSTRACT FROM AUTHOR]

Adenosine-induced acceleration of glycolysis in hearts stressed by transient ischemia is accompanied by suppression of glycogen synthesis and by increases in activity of adenosine 5′-monophosphate-activated protein kinase (AMPK). Because p38 mitogen-activated protein kinase (MAPK) may regulate glucose metabolism and may be activated downstream of AMPK, this study determined the effects of the p38 MAPK inhibitors SB202190 and SB203580 on adenosine-induced alterations in glucose utilization and AMPK activity. Studies were performed in working rat hearts perfused aerobically following stressing by transient ischemia (2 × 10-min ischemia followed by 5-min reperfusion). Phosphorylation of AMPK and p38 MAPK each were increased fourfold by adenosine, and these effects were inhibited by either 5B202190 or SB203580. Neither of these inhibitors directly affected AMPK activity. Attenuation of the adenosine-induced in- crease in AMPK and p38 MAPK phosphorylation by SB202190 and SB203580 occurred independently of any change in tissue ATP-to-AMP ratio and did not alter glucose uptake, but it was accompanied by an increase in glycogen synthesis and glycogen content and by inhibition of glycolysis and proton production. There was a significant inverse correlation between the rate of glycogen synthesis and AMPK activity and between AMPK activity and glycogen content. These data demonstrate that AMPK is likely downstream of p38 MAPK in mediating the effects of adenosine on glucose utilization in hearts stressed by transient ischemia. The ability of p38 MAPK inhibitors to relieve the inhibition of glycogen synthesis and to inhibit glycolysis and proton production suggests that these agents may restore adenosine-induced cardioprotection in stressed hearts. [ABSTRACT FROM AUTHOR]

Loss of cardioprotection by adenosine in hearts stressed by transient ischemia may be due to its effects on glucose metabolism. In the absence of transient ischemia, adenosine inhibits glycolysis, whereas it accelerates glycolysis after transient ischemia. Inasmuch as 5′-AMP-activated protein kinase (AMPK) is implicated as a regulator of glucose and fatty acid utilization, this study determined whether a differential alteration of AMPK activity contributes to acceleration of glycolysis by adenosine in hearts stressed by transient ischemia. Studies were performed in working rat hearts perfused aerobically under normal conditions or after transient ischemia (two 10-mm periods of ischemia followed by 5 mm of reperfusion). LV work was not affected by adenosine. AMPK phosphorylation was not affected by transient ischemia; however, phosphorylation and activity were increased nine- and threefold, respectively, by adenosine in stressed hearts. Phosphorylation of acetyl-CoA carboxylase and rates of palmitate oxidation were unaltered. Glycolysis and calculated proton production were increased 1.8- and 1.7-fold, respectively, in hearts with elevated AMPK activity. Elevated AMPK activity was associated with inhibition of glycogen synthesis and unchanged rates of glucose uptake and glycogenolysis. Phentolamine, an a-adrenoceptor antagonist, which prevents adenosine-induced activation of glycolysis in stressed hearts, prevented AMPK phosphorylation. These data demonstrate that adenosine-induced activation of AMPK after transient ischemia is not sufficient to alter palmitate oxidation or glucose uptake. Rather, activation of AMPK alters partitioning of glucose away from glycogen synthesis; the increase in glycolysis may in part contribute to loss of adenosine-induced cardioprotection in hearts subjected to transient ischemia. [ABSTRACT FROM AUTHOR]

Compares the effects of adenosine and a selective adenosine A1-receptor agonist in aerobically perfused working rat hearts and in hearts exposed to two short episodes of antecedent ischemia designed to partially deplete their glycogen stores. Coupling of glycolysis to glucose oxidation as the key determinant of mechanical function of postischemic myocardium.