Importance of peripheral insulin levels for insulin-induced suppression of glucose production in depancreatized dogs.

It is generally believed that glucose production (GP) cannot be adequately suppressed in insulin-treated diabetes because the portal-peripheral insulin gradient is absent. To determine whether suppression of GP in diabetes depends on portal insulin levels, we performed 3-h glucose and specific activity clamps in moderately hyperglycemic (10 mM) depancreatized dogs, using three protocols: (a) 54 pmol.kg-1 bolus + 5.4 pmol.kg-1.min-1 portal insulin infusion (n = 7; peripheral insulin = 170 +/- 51 pM); (b) an equimolar peripheral infusion (n = 7; peripheral insulin = 294 +/- 28 pM, P < 0.001); and (c) a half-dose peripheral infusion (n = 7), which gave comparable (157 +/- 13 pM) insulinemia to that seen in protocol 1. Glucose production, use (GU) and cycling (GC) were measured using HPLC-purified 6-[3H]- and 2-[3H]glucose. Consistent with the higher peripheral insulinemia, peripheral infusion was more effective than equimolar portal infusion in increasing GU. Unexpectedly, it was also more potent in suppressing GP (73 +/- 7 vs. 55 +/- 7% suppression between 120 and 180 min, P < 0.001). At matched peripheral insulinemia (protocols 2 and 3), not only stimulation of GU, but also suppression of GP was the same (55 +/- 7 vs. 63 +/- 4%). In the diabetic dogs at 10 mM glucose, GC was threefold higher than normal but failed to decrease with insulin infusion by either route. Glycerol, alanine, FFA, and glucagon levels decreased proportionally to peripheral insulinemia. However, the decrease in glucagon was not significantly greater in protocol 2 than in 1 or 3. When we combined all protocols, we found a correlation between the decrements in glycerol and FFAs and the decrease in GP (r = 0.6, P < 0.01). In conclusion, when suprabasal insulin levels in the physiological postprandial range are provided to moderately hyperglycemic depancreatized dogs, suppression of GP appears to be more dependent on peripheral than portal insulin concentrations and may be mainly mediated by limitation of the flow of precursors and energy substrates for gluconeogenesis and by the suppressive effect of insulin on glucagon secretion. These results suggest that a portal-peripheral insulin gradient might not be necessary to effectively suppress postprandial GP in insulin-treated diabetics.     

Characterization of circulating insulin and proinsulin-binding antibodies in autoimmune hypoglycemia.

Five patients with fasting and(or) postprandial hypoglycemia were found to have insulin antibodies in the absence of previously documented immunization. Studies on the equilibrium-binding of insulin to the autoantibodies revealed two classes of binding sites with association constants and binding capacities analogous to those of insulin antibodies from insulin-treated diabetic patients. Similarly, no consistent differences in these parameters were found in both groups of patients with insulins of bovine, porcine, and human origin. Proinsulin (C-segment directed) antibodies capable of binding bovine or porcine proinsulin were present in 10 of 10 and 9 of 10 insulin-treated diabetics serving as controls, respectively, and, when present, provide incontrovertible evidence of exogenous insulin administration. No such antibodies could be detected in the hypoglycemic patients with autoimmune insulin antibodies. The kinetics of dissociation of the insulin-antibody complexes were consistent with the existence of two classes of antibody sites. The corresponding dissociation rate constants were large enough to predict that significant amounts of free hormone may be generated by this mechanism and provide a plausible pathogenesis for the hypoglycemia in these patients.     

Prevention of early-morning hyperglycemia in IDDM patients with long-acting zinc insulin.

OBJECTIVE--To evaluate whether an insulin regimen with a long-acting zinc insulin (Ultratard HM) could help control fasting hyperglycemia in insulin-dependent diabetes mellitus (IDDM) patients. RESEARCH DESIGN AND METHODS--A randomized sequential crossover trial with 6-wk treatment periods was used. Ten IDDM patients from the diabetes clinic at the Medical School who had persistent fasting hyperglycemia (greater than 10 mmol/L) were studied. Patients with nocturnal hypoglycemia were excluded. All patients completed the study. Insulin regimens consisted of three daily injections of a short-acting insulin (Actrapid HM) before meals and either a long-acting zinc insulin (Ultratard HM) or an intermediate isophane insulin (Protaphane HM) before the evening meal. Each regimen was followed for 6 wk. RESULTS--Fasting blood glucose levels (at 06:00 and 08:00) were significantly lower after the long-acting insulin regimen (6.26 +/- 0.88 vs. 10.82 +/- 4.27 mM, P less than 0.05 and 9.26 +/- 1.02 vs. 14.03 +/- 1.08 mM, P less than 0.05, respectively). Plasma-free insulin levels mirrored blood glucose concentrations because they were significantly higher at 06:00 and 08:00 after the long-acting insulin regimen (49.5 +/- 10.1 vs. 20.1 +/- 4.3 pM, P less than 0.05 and 31.6 +/- 5.0 vs. 16.5 +/- 3.4 pM, P less than 0.05, respectively). At any other time of the day, blood glucose and plasma insulin levels were not significantly different with either one of the two insulin regimens. CONCLUSIONS--A long-acting zinc human insulin injected before the evening meal can help to control persistent fasting hyperglycemia in IDDM patients.     

Mechanisms of insulin resistance in experimental hyperinsulinemic dogs.

This study was undertaken to characterize the insulin resistance and the mechanism thereof caused by chronic hyperinsulinemia produced in dogs by surgically diverting the veins of the pancreas from the portal vein to the vena cava. Pancreatic venous diversion (PVD, n = 8) caused a sustained increase in arterial insulin and decrease in portal insulin concentration compared with the control group (n = 6). Hyperinsulinemic euglycemic clamps were conducted 4 wk after surgery. The increase in the glucose disposal rate (GDR) was significantly less in the PVD group (39.0+/-5.0 vs. 27.9+/-3.2 micromol/kg/min, P < 0.01) compared with the control group, but the suppression of hepatic glucose production by insulin was similar for both groups. Muscle insulin receptor tyrosine kinase activity (IR-TKA) increased from 6.2+/-0.4 to 20.3+/-2.7 in the control group, but from 5.8+/-0.5 to only 12.7+/-1.7 fmol P/fmol IR in the PVD group (P < 0.01). With respect to the periphery, the time to half-maximum response (t1/2a) for arterial insulin was the same for both groups, whereas the t1/2a for lymph insulin (30+/-3 vs. 40+/-4 min, P < 0.05) and GDR (29+/-3 vs. 66+/-10 min, P < 0.01) were greater for the PVD group. Chronic hyperinsulinemia led to marked peripheral insulin resistance characterized by decreased insulin-stimulated GDR, and impaired activation of GDR kinetics due, in part, to reduced IR-TKA. Transendothelial insulin transport was impeded and was responsible for one third of the kinetic defect in insulin-resistant animals, while slower intracellular mechanisms of GDR were responsible for the remaining two thirds.     

Insulin-induced hypoglycemia increases hepatic sensitivity to glucagon in dogs

In individuals with type 1 diabetes, hypoglycemia is a common consequence of overinsulinization. Under conditions of insulin-induced hypoglycemia, glucagon is the most important stimulus for hepatic glucose production. In contrast, during euglycemia, insulin potently inhibits glucagon's effect on the liver. The first aim of the present study was to determine whether low blood sugar augments glucagon's ability to increase glucose production. Using a conscious catheterized dog model, we found that hypoglycemia increased glucagon's ability to overcome the inhibitory effect of insulin on hepatic glucose production by almost 3-fold, an effect exclusively attributable to marked enhancement of the effect of glucagon on net glycogen breakdown. To investigate the molecular mechanism by which this effect comes about, we analyzed hepatic biopsies from the same animals, and found that hypoglycemia resulted in a decrease in insulin signaling. Furthermore, hypoglycemia and glucagon had an additive effect on the activation of AMPK, which was associated with altered activity of the enzymes of glycogen metabolism.     

Inhibitory effect of circulating insulin on glucagon secretion during hypoglycemia in type I diabetic patients.

OBJECTIVE--To clarify whether the circulating insulin level influences hormonal responses, glucagon secretion in particular, during hypoglycemia in patients with insulin-dependent (type I) diabetes. RESEARCH DESIGN AND METHODS--Nine type I diabetic patients were studied. During two separate experiments, hypoglycemia was induced by low-dose (244 pmol.kg-1.h-1) and high-dose (1034 pmol.kg-1.h-1) intravenous insulin infusions for 180 min in each case. The arterial blood glucose level was directly monitored every 1.5 min, and glucose was infused in the high-dose test to clamp the arterial blood glucose level to be identical as in the low-dose test. RESULTS--Despite the fact that the plasma insulin level was four times higher in the high-dose than in the low-dose test (740 +/- 50 vs. 180 +/- 14 pM), a close to identical arterial hypoglycemia of approximately 3.3 mM was obtained in the two experiments. During hypoglycemia, a significant rise of the plasma glucagon level was found only in the low-dose test (188 +/- 29 vs. 237 +/- 37 ng/L, P less than 0.05), and the incremental area under the glucagon curve was significantly greater in the low-dose than in the high-dose test (140 +/- 19 vs. -22.7 +/- 34 ng/L.h-1, P less than 0.005). The responses of plasma epinephrine, norepinephrine, growth hormone, pancreatic polypeptide, and somatostatin were similar in both tests and, consequently, were not significantly modified by the circulating insulin level. CONCLUSIONS--This study demonstrates that, in type I diabetic patients, the glucagon response to hypoglycemia is suppressed by a high level of circulating insulin within the physiological range. Our findings may help to explain the impairment of glucagon secretion during hypoglycemia frequently seen in these patients.     

Effects of hypoglycemia and prolonged fasting on insulin and glucagon gene expression. Studies with in situ hybridization.

In situ hybridization of proinsulin and proglucagon mRNA was performed in rat pancreas to assess prohormone gene expression during various glucopenic conditions. During a 4-d fast mean blood glucose declined by 48 mg/dl; proinsulin mRNA signal density remained normal while proglucagon mRNA signal density more than doubled. At the end of a continuous 12-d insulin infusion blood glucose averaged 53 +/- 12 mg/dl; proinsulin mRNA signal density declined to 30% of controls while proglucagon mRNA signal density more than doubled. In insulinoma-bearing NEDH rats blood glucose averaged 34 +/- 3.5 mg/dl; the proinsulin mRNA signal was virtually undetectable and proglucagon mRNA signal density was more than twice the controls. There was no detectable change in either beta-cell area or islet number in rats subjected to fasting or insulin infusion, but in insulinoma-bearing rats beta cell area was markedly reduced. Thus compensation during 4 d of starvation involves an increase in glucagon gene expression without change in insulin gene expression or beta cell mass. In moderate insulin-induced hypoglycemia glucagon gene expression is increased and insulin gene expression decreased. In more profound insulinoma-induced hypoglycemia, in addition to the foregoing changes in hormone gene expression, there is a profound reduction in the number of insulin-expressing cells.     

Effect of the fast-acting insulin analog lispro on the risk of nocturnal hypoglycemia during intensified insulin therapy. U.K. Lispro Study Group.

OBJECTIVE: To measure the effectiveness of insulin lispro, a fast-acting insulin analog, in reducing hypoglycemic episodes when used in a basal bolus regimen by patients with type 1 diabetes using intensive insulin therapy. RESEARCH DESIGN AND METHODS: In 11 diabetes outpatient clinics in the U.K., 165 subjects with type 1 diabetes were enrolled in a randomized crossover open-label study with a 2-month run-in period and then treated with a basal bolus regimen. Patients used human NPH insulin at night with either premeal insulin lispro for 4 months followed by human regular insulin for another 4 months or human regular insulin for 4 months followed by insulin lispro for another 4 months. The main outcome measures were the number of hypoglycemic episodes during both treatments and HbA1c level. RESULTS: A total of 135 patients were randomized, with 68 receiving insulin lispro and 67 receiving human regular insulin for the first 4 months. The data for the first 4 months of treatment only were compared as two independent groups because of a period effect and a treatment-period interaction. Glycemic control was equally tight during treatment with human regular insulin (HbA1c, 6.2 +/- 0.8%) and insulin lispro (6.0 +/- 0.9%). A total of 1,156 hypoglycemic episodes occurred during treatment with human regular insulin compared with 775 hypoglycemic episodes that occurred during treatment with insulin lispro (P = 0.04). This difference was chiefly because of a reduced number of nocturnal episodes (181 vs. 52, P = 0.001) in the insulin lispro group. CONCLUSIONS: The use of a fast-acting insulin analog, insulin lispro, as part of a basal bolus regimen reduces nocturnal hypoglycemia in patients with type 1 diabetes who maintain tight glycemic control during intensive insulin therapy.     

The effect of meal feeding and of sham-feeding on insulin secretion in dogs.

After feeding intact conscious dogs 1000 g mashed meat, peripheral venous immunoreactive insulin activity (IRI) increases before any enhancement of amino nitrogen concentration. This course of IRI is paralleled by a decrease of free fatty acids. Meal feeding in dogs, whose pancreatic juice is completely diverted from the gut by a fistula, is followed by a similar IRI increase without a distinct enhancement of amino nitrogen. In oesophagus fistula dogs, sham-feeding meat in 9 out of 15 experiments results in a considerable early IRI increase which is correlated with a small but a significant decrease of blood glucose and free fatty acid concentrations. In these tests there was no amino nitrogen alteration either.     

Weight-based, insulin dose-related hypoglycemia in hospitalized patients with diabetes

OBJECTIVE

To determine the association of weight-based insulin dose with hypoglycemia in noncritically ill inpatients with diabetes.

RESEARCH DESIGN AND METHODS

We performed a retrospective, case-control study of 1,990 diabetic patients admitted to hospital wards. Patients with glucose levels <70 mg/dL (case subjects) were matched one to one with nonhypoglycemic control subjects on the basis of the hospital day of hypoglycemia, age, sex, and BMI.

RESULTS

Relative to 24-h insulin doses <0.2 units/kg, the unadjusted odds of hypoglycemia increased with increasing insulin dose. Adjusted for insulin type, sliding-scale insulin use, and albumin, creatinine, and hematocrit levels, the higher odds of hypoglycemia with increasing insulin doses remained (0.6–0.8 units/kg: odds ratio 2.10 [95% CI 1.08–4.09], P = 0.028; >0.8 units/kg: 2.95 [1.54–5.65], P = 0.001). The adjusted odds of hypoglycemia were not greater in patients who received 0.2–0.4 units/kg (1.08 [0.64–1.81], P = 0.78) or 0.4–0.6 units/kg (1.60 [0.90–2.86], P = 0.11). Although the relationship between insulin dose and hypoglycemia did not vary by insulin type, patients who received NPH trended toward greater odds of hypoglycemia compared with those given other insulins.

CONCLUSIONS

Higher weight-based insulin doses are associated with greater odds of hypoglycemia independent of insulin type. However, 0.6 units/kg seems to be a threshold below which the odds of hypoglycemia are relatively low. These findings may help clinicians use insulin more safely.Treatment with insulin in hospitalized patients is a well-recognized risk factor for hypoglycemia. Although this clearly has been demonstrated in critically ill patients treated with continuous intravenous insulin (1), evidence regarding subcutaneous insulin in non–critical-care settings is lacking. Physicians may underdose insulin in fear of hypoglycemia because there is uncertainty about the dose-response relationship between insulin and hypoglycemia in noncritically ill inpatients with diabetes (2,3).Current guidelines on inpatient diabetes management call for basal-bolus insulin therapy for hospital-ward patients (4–6), in which one approach to determining insulin dose is based on weight (i.e., total daily units per kilogram of body weight). The initial daily insulin doses of basal-bolus protocols vary widely, from 0.3 to 1.5 units/kg (5,7–10). Rates of hypoglycemia in randomized trials using 0.4–0.5 units/kg/day of insulin range from 3 to 33% of subjects (9,11). Furthermore, these studies excluded patients with known risk factors for hypoglycemia, such as renal impairment. Despite the use of relatively high insulin doses in clinical practice, the risk of hypoglycemia with higher weight-based doses has not been established. A better understanding of the relationship between insulin dose and hypoglycemia may facilitate more effective dosing, thus reducing the risk of hypoglycemia and hyperglycemia.We performed a retrospective, case-control study of patients with diabetes admitted to general hospital wards to investigate the relationship between insulin dose and hypoglycemia. It was hypothesized that higher weight-based insulin doses are associated with a greater risk of hypoglycemia. Furthermore, we predicted that the association of insulin dose with hypoglycemia varies by type of insulin regimen, with glargine-based regimens being associated with less hypoglycemia than NPH-based regimens.     

The effect of systemic venous drainage of the pancreas on insulin sensitivity in dogs.

To assess the metabolic consequences of the diversion of the pancreatic venous drainage to the systemic circulation, the pancreaticoduodenal and gastrosplenic veins were anastomosed to the inferior vena cava in nine normal dogs. This procedure maintained the integrity of the entire pancreas while shunting the hormonal output of the pancreas to the periphery. The metabolic effects were assessed from the sensitivity to insulin during a euglycemic hyperinsulinemic glucose clamp using an insulin infusion of 800 microU/kg per min. The studies were controlled by their duplication in seven dogs identically treated but with the pancreatic veins reanastomosed to the portal vein. No differences in systemic insulin levels or insulin sensitivity before and after surgery were seen under these circumstances. After diversion, however, basal insulin levels rose from 4.5 +/- 1.0 to 11.5 +/- 2.5 microU/ml. Basal glucose metabolic clearance rate (MCR) rose to 3.0 +/- 0.4 from 2.0 +/- 0.3 ml/kg per min. On insulin infusion, maximal stimulation of MCR within the 2-h infusion period was to 15.2 +/- 2.5 ml/kg per min preoperatively and to 7.2 +/- 0.8 ml/kg per min after diversion. Using ratios of MCR-to-insulin concentration as an index of insulin sensitivity, it was demonstrated that this index decreased by at least 50% after diversion. These data imply that portal venous drainage of the pancreas is an important factor in the determination of peripheral insulin sensitivity.     

Less hypoglycemia with insulin glargine in intensive insulin therapy for type 1 diabetes. U.S. Study Group of Insulin Glargine in Type 1 Diabetes

OBJECTIVE: Insulin glargine (21A-Gly-30Ba-L-Arg-30Bb-L-Arg-human insulin) is a biosynthetic insulin analog with a prolonged duration of action compared with NPH human insulin. This study compared insulin glargine with NPH human insulin in subjects with type 1 diabetes who had been previously treated with multiple daily injections of NPH insulin and regular insulin. RESEARCH DESIGN AND METHODS: This study was a multicenter randomized parallel-group study in which subjects were randomized to receive premeal regular insulin and either insulin glargine (at bedtime) or NPH insulin (at bedtime for patients on once-daily therapy and at bedtime and in the morning for patients on twice-daily therapy) for up to 28 weeks. Dose titration of both basal insulins was based on capillary fasting whole blood glucose (FBG) levels; the goal was a premeal blood glucose concentration of 4.4-6.7 mmol/l. RESULTS: A total of 534 well-controlled type 1 diabetic subjects (mean GHb 7.7%, mean fasting plasma glucose [FPG] 11.8 mmo/l) were treated. A small decrease in GHb levels was noted with both insulin glargine (-0.16%) and NPH insulin (-0.21%; P > 0.05). Significant reductions in median FPG levels from baseline (-1.67 vs. -0.33 mmol/l with NPH insulin, P = 0.0145) and a trend for a reduction in capillary FBG levels were achieved with insulin glargine. After the 1-month titration phase, significantly fewer subjects receiving insulin glargine experienced symptomatic hypoglycemia (39.9 vs. 49.2%, P = 0.0219) or nocturnal hypoglycemia (18.2 vs. 27.1%, P = 0.0116) with a blood glucose level <2.0 mmol/l compared with subjects receiving NPH insulin. CONCLUSIONS: Lower FPG levels with fewer episodes of hypoglycemia were achieved with insulin glargine compared with once- or twice-daily NPH insulin as part of a basal-bolus regimen in patients with type 1 diabetes.