Insulin and adrenergic effects during endotoxin shock: in vivo myocardial interactions

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Abstract
Study objective – Catecholamine concentrations are raised during endotoxin shock and may be responsible for myocardial insulin resistance in such a condition. The purpose of the investigation was to examine the effect of insulin on myocardial contractility and glucose uptake in the presence of β adrenergic blockade during endotoxin shock. Design – Endotoxin shock was obtained in dogs by giving S Typhimurium endotoxin intravenously (1 mg·kg−1) and the cardiac responses to insulin were determined under hyperinsulinaemic (4 U·min−1) euglycaemic clamp conditions during continuous β adrenergic blockade (propranolol 150 μg·kg−1 + 5 μg·kg−1). Subjects – 19 mongrel dogs of either sex, weight 20-25 kg, were studied under pentobarbitone anaesthesia. Seven dogs received endotoxin plus propranolol, and seven others received propranolol alone (control group). Five dogs received endotoxin but no propranolol or insulin. All other procedures were the same in each group. Measurements and results – The exposed heart was prepared for coronary sinus blood sampling and measurements of circumflex artery blood flow (Q), instantaneous left ventricular pressure, and left ventricular wall thickness. Glucose uptake was calculated from product of Q and aortic-coronary sinus concentration difference. End systolic pressure-dimension relationship was used to assess contractility. Myocardial performance was assessed from left ventricular dP/dtmax. Basal shock measurements were made 60 min post endotoxin, β Adrenergic blockade did not interfere with insulin stimulated glucose uptake in controls, but was unable to restore the uptake response during endotoxin shock. Contractility was increased during endotoxin shock and this effect was abolished by β adrenergic blockade. In controls the only variable affected by β adrenergic blockade was left ventricular dP/dtmax (decreased). Insulin increased contractility during β adrenergic blockade in controls but not in shock. Myocardial performance was depressed during shock. In controls, insulin increased myocardial performance; in shock this response was attenuated. Conclusions – The findings confirm that the myocardium becomes less responsive to the glucose uptake stimulating and positive inotropic effects of insulin during endotoxin shock. The data show that β adrenergic activity is responsible for the increased contractile state of the heart during acute endotoxin shock, but is not the cause of the observed insulin resistant state.