Cornel Dobrescu

Insulin-mediated glucose uptake by individual tissues during sepsis

Gram-negative hypermetabolic sepsis has been previously reported to produce whole body insulin resistance. The present study was performed to determine in vivo which tissues are responsible for the sepsis-induced decrease in insulin-mediated glucose uptake (IMGU), and whether that decrease was related to a change in regional blood flow. Vascular catheters were placed in rats and sepsis was induced by subcutaneous injections of Escherichia coli. Insulin action was assessed 20 hours after the first injection of bacteria by the combined use of the euglycemic hyperinsulinemic clamp and the tracer 2-deoxyglucose (dGlc) technique. Insulin was infused at various rates in separate groups of septic and nonseptic rats for 3 hours to produce steady-state insulin levels between 70 and 20,000 microU/mL. Rats were injected with [U-14C]-dGlc 140 minutes after the start of the euglycemic hyperinsulinemic clamp for the determination of the glucose metabolic rate (Rg) in selected tissues. The maximal response to insulin was decreased 30% to 40% in the gastrocnemius, and in the red and white quadriceps. The former two muscles also showed a decrease in insulin sensitivity. However, the insulin resistance seen in hindlimb muscles was not evident in all muscles of the body, since IMGU by abdominal muscle, diaphragm, and heart was not impaired by sepsis. The basal Rg by skin, spleen, ileum, and lung was increased by sepsis, and was higher than the insulin-stimulated increases in Rg by these tissues in nonseptic animals. Cardiac output was similar in septic and nonseptic rats and did not change during the infusion of insulin. Under basal conditions, sepsis appeared to redistribute blood flow away from the red quadriceps and skin, and increased flow to the liver (arterial), lung, and small intestine. When plasma insulin levels were elevated, hepatic arterial blood flow was increased, and flow to the red quadriceps and skin was decreased in nonseptic animals. Hyperinsulinemia did not produce any consistent change in regional blood flow in septic animals. The results of this study indicate that a decrease rate of IMGU in muscle is primarily responsible for the whole body insulin resistance seen during hypermetabolic sepsis, and that the impairment of insulin action in skeletal muscle is not dependent on fiber type or to changes in blood flow.

Sepsis-induced increases in glucose uptake by macrophage-rich tissues persist during hypoglycemia

The purpose of the present study was to determine how hypoglycemia alters glucose uptake by individual tissues and whether this response is altered by gram-negative infection. A hypermetabolic septic state was produced in catheterized rats by subcutaneous injections of live Escherichia coli. The next morning, animals were infused with saline, somatostatin to produce a euglycemic insulinopenic state (6 mmol/L glucose, 5 microU/mL insulin), or 3-mercaptopicolinate (3-MP) to inhibit gluconeogenesis and produce a hypoglycemic insulinopenic (4.5 or 2 mmol/L glucose, 5 microU/mL insulin) condition. After 140 minutes, [14C]2-deoxyglucose was injected intravenously (IV) to determine in vivo glucose uptake by individual tissues. Sepsis increased whole body glucose disposal (Rd) by 53% under basal euglycemic conditions and this increase resulted from an enhanced rate of glucose removal by liver, spleen, lung, ileum, and skin. Under euglycemic insulinopenic conditions, total glucose Rd decreased in both septic and nonseptic rats as a result of a decreased rate of glucose uptake by muscle. However, because the absolute rate of glucose uptake was still elevated by sepsis, the rate of non-insulin-mediated glucose uptake (NIMGU) was 46% higher in septic rats than in nonseptic animals. Severe hypoglycemia (2 mmol/L) produced a relative insulin deficiency and decreased whole body Rd in both septic and nonseptic animals by 53% to 58%, compared with euglycemic insulinopenic animals. The decrease in blood glucose decreased glucose uptake by all tissues examined, except brain and heart. However, sepsis still increased glucose uptake by liver, spleen, lung, ileum, and skin (25% to 90%), compared with hypoglycemic nonseptic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-1 induced increases in glucose utilization are insulin mediated

Interleukin-1 (IL-1) is known to modulate a variety of the acute-phase responses to infection. Since an enhanced rate of whole-body glucose utilization is a consistent feature of the hypermetabolic phase of infection, the purpose of the present study was to determine whether IL-1 could increase glucose uptake and whether that increase was dependent on the concomitant elevation in plasma insulin. Glucose utilization (Rg) of different tissues was investigated in vivo by the 2-deoxyglucose tracer technique. Human purified IL-1 was administered to chronically, catheterized conscious rats and increased the plasma insulin levels and the Rg in macrophage-rich tissues, including the lung, spleen, liver and skin. IL-1 also increased Rg in skeletal muscle and diaphragm. To eliminate the insulin-stimulated increase in Rg, somatostatin (SRIF) was infused 1 h prior to IL-1. SRIF prevented the IL-1 induced increase in insulin and tissue glucose utilization. IL-1 administration to streptozotocin-induced diabetic rats also failed to increase Rg in any tissue examined. These data suggest that the administration of IL-1 increases organ glucose utilization by insulin-dependent mechanisms.

Attenuation of burn-induced changes in hemodynamics and glucose metabolism by the PAF antagonist SRI 63-675.

The importance of platelet-activating factor (PAF) in producing hypotension, hemoconcentration and alterations in carbohydrate metabolism following thermal injury was investigated in chronically catheterized rats. Animals were fasted overnight, anesthetized with pentobarbital, and then injected with saline or the PAF antagonist SRI 63-675 prior to a 25% body surface area scald injury. Burned animals showed a sustained 20-30% fall in mean arterial pressure that was attenuated by the PAF antagonist. Burn also produced a prolonged increase in hematocrit. Animals pretreated with SRI 63-675 showed a similar degree of polycythemia after 1 h, but thereafter hematocrit fell and was not different from sham-burned animals. Burn increased the plasma glucose (45-52%) and lactate (5-6 fold) concentrations, and tended to produce an early increase and a later decrease in the rate of glucose appearance (Ra). These metabolic changes were associated with elevated plasma levels of glucagon and catecholamines. The PAF antagonist prevented the hyperglycemia, reduced the hyperlactacidemia, and prevented the late fall of glucose Ra. Treated animals still showed increased levels of glucagon, while catecholamine concentrations were reduced by 50%. Short-term survival (4 h) was markedly improved (86 vs. 43%). These results suggest that PAF produced following thermal injury is responsible, at least in part, for the early hemodynamic changes and hemoconcentration. However, the role of PAF as a mediator of burn-induced glucose dyshomeostasis appears secondary to its hemodynamic effects.

Myocardial Substrate Utilization in Acute and Chronic, and in Latent and Severe Diabetes

The multiple metabolic manifestations of diabetes have been extensively investigated both in man and in experimental animals. Several procedures have been used to produce experimental models of diabetes which resemble, to a greater or lesser extent, the human disease. Some studies have utilized these models in the acute state, whereas others employed more chronic conditions. The severity of the diabetic state may also vary from one experimental model to another. Although these variables may have an important bearing on the outcome of experimental studies, only scattered reports are available concerning the influence of duration or severity of the diabetic state on the experimental results.