Influence of Feeding and Intracoronary Dose on Insulin‐Mediated Relative Akt Phosphorylation in the Porcine Myocardium

Abstract

SUMMARYAims: Insulin promotes Akt-dependent prosurvival signaling and reduces experimental ischemia reperfusion injury, but its clinical impact has been limited. Further understanding of the interplay between insulin and Akt in the myocardium of relevant large animal models is needed. We aimed to investigate (1) Akt phosphorylation, (2) influence of feeding state, and (3) impact of dose on the Akt response following intracoronary insulin administration in the nonischemic porcine heart. Methods: Pigs fed 2 h preprocedure received 0.1 U (unit) or 1.0 U of insulin in the left coronary artery and fasting pigs 0.1 U. Left and right ventricle tissues harvested 15 min postinsulin administration were analyzed for Akt phosphorylation by densitometric analyses of total Akt and phosphorylated Akt immunoblots expressed as a ratio and normalized against left auricle biopsies at baseline. Results: Median relative Akt phosphorylation across all biopsy locations increased significantly from baseline in both fasting and fed animals after insulin infusion: 371.4% (P < 0.001) in the fasting-0.1 U insulin group, 202.7% (P = 0.003) in the fed-1.0 U group and 131.5% (P < 0.001) in the fed-0.1 U group. The increase was significantly higher for the fasting-0.1 U and the fed-1.0 U groups as compared with the fed-0.1 U group. Baseline serum glucose in fed and fasting pigs was 6.3 AE 0.3 versus 5.2 AE 0.4 mM (P = 0.050), respectively. Conclusions: Preexperimental feeding attenuates the median relative rise in Akt phosphorylation mediated by exogenous insulin in the porcine heart, and higher insulin doses are therefore required in fed compared with fasting animals.

Reperfusion Therapy with Low‐Dose Insulin or Insulin‐Like Growth Factor 2; Myocardial Function and Infarct Size in a Porcine Model of Ischaemia and Reperfusion

“…). In fasting pigs, a corresponding dose of intracoronary insulin (1.8‐2.3 mU/kg) was administered without causing severe hypoglycaemia and was shown to stimulate Akt phosphorylation . The amount of IGF2 administered, 2 μg/kg, was decided from our previous study demonstrating an anti‐apoptotic effect when administered intracoronarily together with blood cardioplegia, resulting in a total amount of 0.252 μg/kg .…”

Insulin Postconditioning Reduces Infarct Size in the Porcine Heart in a Dose-Dependent Manner

“…9 The chosen insulin doses phosphorylated Akt in the nonischemic porcine myocardium, and the relative activation from baseline to 15 minutes after infusion did not differ between the fasted Ins 0.1U and fed Ins 1.0U pigs. 14 Based on this result, the 2 highest physiologically tolerated insulin doses should act similarly on caspase-3 cleavage, assuming Akt-signaling was responsible for the insulin-mediated antiapoptotic effect. 11 However, systemic administration of low-dose insulin during the first 15 minutes of reperfusion did neither reduce IS nor apoptosis in an open thorax porcine model of ischemia–reperfusion, 36 which corresponds with our findings.…”

“…Twenty-seven female mixed-breed Norwegian landrace and Yorkshire pigs weighing 48 ± 4 kg were acclimatized for at least 1 week in the animal facility at the University of Bergen. Female pigs were chosen due to reported higher survival rates and better preserved hemodynamics in female compared to male piglets when subjected to hemorrhagic shock and cardiac arrest 14 and also due to paucity of clinical and experimental cardiovascular research in female subjects. Feeding routines were in accordance with recommendations for slaughter pigs and included 1500 g of Format (FORMAT Norm FKNR.…”

“…Insulin doses were based on previous studies on tolerability and effects on Akt signaling in the nonischemic pig heart, and only the dosing regimens with the presumed largest potential were further examined. 12,14 Briefly summarized, administration of higher doses than 0.1U induced hypoglycemia, hypokalemia, and catecholamine elevation in fasted pigs and was considered harmful in a setting of acute myocardial infarction (AMI). Fed animals tolerated more insulin, 1.0U.…”

“…In previous studies, we have shown that feeding attenuates insulin-related activation of Akt in the pig heart, but this can be overcome by increasing the insulin dose, since fed animals also have higher tolerance. 12,14 Evidence of IS reduction in large animal studies has the potential advantage to mimic the whole interventional treatment procedure and to better determine whether reperfusion therapy with insulin could be a candidate for a clinical trial. The aim of the current study was to explore the effects of pharmacological postconditioning with assumed optimal doses of intracoronary insulin on IS, apoptosis, metabolism, and cardiac function in fasted and fed pigs, using a clinically relevant experimental model.…”