Metabolic effects of high doses of insulin during acute left ventricular failure in dogs

Insulin versus Lipid Emulsion in a Rabbit Model of Severe Propranolol Toxicity: A Pilot Study

Background and objective. Beta-blocker overdose may result in intractable cardiovascular collapse despite conventional antidotal treatments. High dose insulin/glucose (ING), and more recently intravenous lipid emulsion (ILE), have been proposed as potentially beneficial therapies in beta blocker intoxication. We compare efficacy of the novel antidotes ING, with ILE, in a rabbit model of combined enteric/intravenous propranolol toxicity. Methods. Sedated, mechanically ventilated and invasively monitored New Zealand White rabbits underwent mini-laparotomy and enterostomy formation with 40 mg/kg propranolol instilled into the proximal small bowel. At 30 minutes propranolol infusion was commenced at 4 mg/kg/hr and continued to a target mean arterial pressure (MAP) of 50% baseline MAP. Animals were resuscitated with insulin at 3 U/kg plus 0.5 g/kg glucose (ING group), or 10 mL/kg 20% Intralipid (ILE group). Results. Rate pressure product (RPP; RPP = heart rate × mean arterial pressure) was greatest in the ING group at 60 minutes (P < .05). A trend toward greater heart rate was observed in the ING group (P = .06). No difference was observed in survival between groups (4/5 ING versus 2/5 ILE; P = .524). Conclusions. High dose insulin resulted in greater rate pressure product compared with lipid emulsion in this rabbit model of severe enteric/intravenous propranolol toxicity.

Both glucose-insulin-potassium and glutamine in warm blood cardioplegia increase the rates of myocardial glucose and free fatty acid oxidation

OBJECTIVE

We wanted to assess the effect of glucose-insulin-potassium (GIK) and glutamine on the oxidative metabolism during and after prolonged warm continuous blood cardioplegia (WB).

DESIGN

WB was given to 21 pigs divided into three equally sized groups: WB (control), WB and GIK, or WB and glutamine. Oxidation rates of radiolabeled glucose (14C) and free fatty acid (FFA) (3H) were assessed before, during, and at 30 and 60 min after 3 h of cardiac arrest with WB.

RESULTS

During standstill the substrate oxidation dropped markedly (<60%), glucose oxidation was highest in the WB + GIK group (p < 0.05) and FFA oxidation highest in the WB + glutamine group (NS). During recovery the GIK group had an elevated glucose oxidation (47 and 40% vs WB at 30 and 60 min recovery, respectively -p < 0.05). Following 30 min recovery the addition of GIK suppressed FFA oxidation some 60%. Glutamine increased the oxidation of both glucose (30%) and FFA (150%) following 60 min recovery (p < 0.05). During the whole recovery phase the relative FFA oxidation was significantly lowered in the GIK group. There were no differences between the groups regarding arterial levels or uptake of substrates, except for a higher myocardial oxygen consumption (MVO2) during cardioplegia in the glutamine group. All the hearts performed similarly.

CONCLUSION

Addition of GIK or glutamine to the well-perfused and oxygenated heart during WB led to a postcardioplegic increase in oxidative metabolism and MVO2. GIK resulted in a significant metabolic shift from FFA to glucose.

Effect of plasma insulin level on myocardial blood flow and its mechanism of action

Considerable evidence suggests that coronary endothelium regulates myocardial blood flow and metabolism by elaborating vasoactive substances. The physiologic signals mediating this process are uncertain. To test the hypothesis that the process is influenced by physiologic variation in local insulin concentration, we examined the effect of direct intracoronary insulin infusion on myocardial blood flow and oxidative substrate metabolism in 10 patients with coronary heart disease. Ten men (aged 51 to 68 years) who were fasting received a 60-minute intracoronary infusion of insulin at a rate (10 mU/min) sufficient to raise coronary venous plasma insulin from 12+/-4 to 133+/-17 mU/ml without increasing the systemic insulin level. Local coronary hyperinsulinemia increased coronary sinus blood flow in every subject, from 50+/-4 to 61+/-6 ml/min (p<0.01). Insulin also increased myocardial uptake of glucose (from 6+/-1 to 17+/-6 mmol/min) and lactate (from 8+/-2 to 12+/-5 mmol/min), resulting in approximately 30% increase in total oxidative substrate uptake, but without increasing myocardial oxygen consumption (7.0+/-0.7 vs. 7.1+/-0.8 ml/min). Thus, physiologic elevation in the local plasma insulin concentration increases coronary blood flow in the absence of any increase in myocardial oxygen demand or consumption, suggesting a primary reduction in coronary tone, while simultaneously restraining the oxidation of imported substrates. These observations are consistent with insulin-mediated elaboration of vasoactive and/or paracrine factors within the coronary circulation.