Glycemia and the cardioprotective effects of insulin pre-conditioning in the isolated rat heart

摘要

Background While acute hyperglycemia has been shown to mitigate the beneficial effects of ischemic preconditioning, its effect on insulin-induced preconditioning remains unclear. Methods The study was designed to test the hypothesis that acute hyperglycemia diminishes the cardioprotective effects following a 20-min pre-ischemic pre-conditioning with insulin in the isolated rat heart using the Langendorff system. Forty hearts were assigned to receive modified Krebs–Henseleit (KH) buffer containing 0.5?U/L insulin and 100?mg/dL glucose (InsG100, n?=?10), KH buffer with 100?mg/dL glucose (G100, n?=?10), KH buffer supplemented with 0.5?U/L insulin and 600?mg/dL glucose (InsG600, n?=?10), or with 600?mg/dL glucose (G600, n?=?10). To match the osmotic pressure of the InsG600 group, 27.5?mmol/L of mannitol was added to KH solution in the InsG100 and G100 group. The four groups were perfused with each solution for 20?min prior to 15?min of no-flow ischemia, and during 20?min of reperfusion. Only during the ischemic period the heart was paced at 222?beats/min. Measurements of heart rate, coronary flow and maximum of LV derivative of pressure development (dP/dt max) were recorded. Myocardial phospho-protein kinase B (p-Akt) and tumor necrosis factor-α (TNF-α) levels were assayed by enzyme-linked immunosorbent assay and sandwich ELISA, respectively following reperfusion. Results After reperfusion, LV dP/dt max and heart rate in the InsG100 group was significantly higher than that in the other three groups. The myocardial p-Akt level in the InsG100 group was significantly elevated when compared to the InsG600 group at the end of reperfusion. The p-Akt levels in the InsG600 and InsG100 group were significantly higher than in the corresponding non-insulin groups. Conclusions Acute hyperglycemia diminishes the cardioprotective effects of insulin preconditioning in the isolated rat heart, possibly mediated through the suppression of myocardial Akt phosphorylation.