Signalling pathways involved in insulin cardioprotection : are they comparable in normoxic perfused isolated rat heart vs. ischaemia/reperfusion model?

[摘要] ENGLISH ABSTRACT: Introduction: It is well documented that insulin offers cardioprotectionagainst the consequences of ischaemia/reperfusion injury. Insulin-inducedimprovements in cardiac functions are widely investigated in models ofischaemia and reperfusion. It has been shown that many signalling pathwaysmay be involved in the cardioprotection properties of insulin under thoseconditions. These pathways include PI3-K, PKB/Akt, p70S6k, ERK and manyothers. However, little data exists on the effects of insulin on the heart undernormoxic condition. Some evidence has been presented that insulin has apositive inotropic effect on the normoxic perfused rat heart, but no precisecellular mechanism has been investigated or described in this regard. Webelieve that an investigation into the effects of insulin on cardiac function andpathways involved under normoxic conditions may help us to betterunderstand the mechanisms of insulin-induced cardioprotection. Aims: Todetermine a suitable dose of insulin at which a positive inotropic responsecould be detectable under normoxic conditions, to investigate the possiblemechanisms involved in insulin-induced increases in contractility with specificreference to the vasculature and the coronary flow and to investigate apossible involvement of PI3-K and its downstream effectors on the insulineffects on cardiac functions under normoxic conditions. Materials andmethods: Isolated rat hearts were perfused retrogradely using theLangendorff technique. After 10 minutes of stabilization hearts were perfusedfor 30 minutes either with standard perfusion solution i.e. Krebs-Henseleitbuffer + glucose gassed with 95%O2, 5%CO2 (control hearts), or withstandard perfusion solution plus insulin alone or insulin together with the nitric oxide synthase inhibitor L-NAME or the PI3-K inhibitor wortmannin. Leftventricular developed pressure (LVDevP), heart rate (HR) and coronary flow(CF) as well as phosphorylated PI3-K and PKB/Akt in heart were measured.Results: Administration of insulin alone at physiological concentrationsshowed improved cardiac function compared to hearts in the control group.Hearts that received insulin+L-NAME showed a significant decrease infunction compared to the control hearts and the hearts that received insulinalone (p<0.05). Phosphorylated PKB/Akt (Thr308) was increased in heartsthat received insulin alone and insulin+L-NAME compared to the controlhearts. Phosphorylated PI3-K tended to be higher in hearts where insulin wasadministered alone compared to the hearts that received insulin+L-NAME orinsulin+wortmannin. Conclusion: This study confirmed that physiologicalconcentrations of insulin exert positive inotropic effects on cardiac function innormoxic perfused rat hearts as seen with the improved LVDevP. Inhibition ofPI3-K by wortmannin induced a decrease in phosphorylated PKB/Akt inhearts that received insulin+wortmannin and administration of L-NAMEimpaired the beneficial effects of insulin on cardiac functions. Therefore theseresults may indicate that nitric oxide may have a role in the positive effect ofinsulin on cardiac function in the healthy heart perfused under normoxicconditions. L-NAME as well as wortmannin reversed the positive inotropiceffects of insulin. Both inhibitors also unmasked effects of insulin via nitricoxide and PI3-K on heart rate and coronary flow.

[发布机构] Stellenbosch University