Mechanisms of hyperglycemia-induced insulin resistance in whole body and skeletal muscle of type I diabetic patients.

To examine the mechanisms of hyperglycemia-induced insulin resistance, eight insulin-dependent (type I) diabetic men were studied twice, after 24 h of hyperglycemia (mean blood glucose 20.0 +/- 0.3 mM, i.v. glucose) and after 24 h of normoglycemia (7.1 +/- 0.4 mM, saline) while receiving identical diets and insulin doses. Whole-body and forearm glucose uptake were determined during a 300-min insulin infusion (serum free insulin 359 +/- 22 and 373 +/- 29 pM, after hyper- and normoglycemia, respectively). Muscle biopsies were taken before and at the end of the 300-min insulin infusion. Plasma glucose levels were maintained constant during the 300-min period by keeping glucose for 150 min at 16.7 +/- 0.1 mM after 24-h hyperglycemia and increasing it to 16.5 +/- 0.1 mM after normoglycemia and by allowing it thereafter to decrease in both studies to normoglycemia. During the normoglycemic period (240-300 min), total glucose uptake (25.0 +/- 2.8 vs. 33.8 +/- 3.9 mumol.kg-1 body wt.min-1, P less than 0.05) was 26% lower, forearm glucose uptake (11 +/- 4 vs. 18 +/- 3 mumol.kg-1 forearm.min-1, P less than 0.05) was 35% lower, and nonoxidative glucose disposal (8.9 +/- 2.2 vs. 19.4 +/- 3.3 mumol.kg-1 body wt-1min-1, P less than 0.01) was 54% lower after 24 h of hyper- and normoglycemia, respectively. Glucose oxidation rates were similar. Basal muscle glycogen content was similar after 24 h of hyperglycemia (234 +/- 23 mmol/kg dry muscle) and normoglycemia (238 +/- 22 mmol/kg dry muscle). Insulin increased muscle glycogen to 273 +/- 22 mmol/kg dry muscle after 24 h of hyperglycemia and to 296 +/- 33 mmol/kg dry muscle after normoglycemia (P less than 0.05 vs. 0 min for both). Muscle ATP, free glucose, glucose-6-phosphate, and fructose-6-phosphate concentrations were similar after both 24-h treatment periods and did not change in response to insulin. We conclude that a marked decrease in whole-body, muscle, and nonoxidative glucose disposal can be induced by hyperglycemia alone.     

Survival benefits of intensive insulin therapy in critical illness: impact of maintaining normoglycemia versus glycemia-independent actions of insulin

Tight blood glucose control with insulin reduces morbidity and mortality of critically ill patients. However, the relative impact of maintaining normoglycemia and of glycemia-independent actions of insulin remains unknown. We therefore independently manipulated blood glucose and plasma insulin levels in burn-injured, parentally fed rabbits over 7 days to obtain four study groups: two normoglycemic groups with either normal or elevated insulin levels and two hyperglycemic groups with either normal or elevated insulin levels. We studied the relative impact of glycemia and glycemia-independent effects of insulin on survival; myocardial contractility in an open chest preparation; endothelial function in isolated aortic rings; and liver, kidney, and leukocyte function in a rabbit model of critical illness. Mortality was significantly lower in the two normoglycemic groups independent of insulin levels. Maintaining normoglycemia, independent of insulin levels, prevented endothelial dysfunction as well as liver and kidney injury. To increase myocardial systolic function, elevated insulin levels and prevention of hyperglycemia were required concomitantly. Leukocyte dysfunction was present in the two hyperglycemic groups, which could in part be rescued by insulin. The results suggest that the observed benefits of intensive insulin therapy required mainly maintenance of normoglycemia; whereas glycemia-independent actions of insulin exerted only minor, organ-specific impact.     

Differential sensitivity of glycogenolysis and gluconeogenesis to insulin infusions in dogs.

The suppressive effect of insulin on hepatic glucose production is generally recognized. Though it is well established that this effect is at least partially due to inhibition of glycogenolysis, controversy still exists about insulin's effect on gluconeogenesis. The present study was undertaken to determine whether insulin could affect gluconeogenesis from alanine in the intact dog and to compare the effect of insulin on glycogenolysis and gluconeogenesis. In anesthetized dogs fasted overnight, blood samples were drawn simultaneously from a femoral artery and hepatic vein. Alanine-U-14C, 10 mu Ci./kg., was infused over 110 minutes. A constant insulin infusion at either 1 or 5 mU./kg./min. was begun at 50 minutes, and blood glucose concentration was maintained by a variable glucose infusion. When insulin was infused at 1 mU./kg./min., resulting in plasma immunoreactive insulin (IRI) levels of 73 +/- 10 muU./ml., the net splanchnic glucose production (NSGP) was suppressed from 2.7 +/- 2 mg./kg./min. to virtually zero. In constrast, this small increment in insulin concentration had no demonstrable effect on the net splanchnic uptake of alanine or on the conversion of plasma alanine to glucose (7.9 +/- 0.3 mu mol/min.). Insulin infused at 5 mU./kg./min. resulted in IRI levels of 240 +/- 25 muU./ml. This higher insulin concentration was associated with a marked suppression of both the NSGP (100 per cent) and the conversion of plasma alanine to glucose (90 per cent) but did not affect the extraction of alanine by the splanchnic bed. Doses of both 1 and 5 mU./kg./min. were associated with a 35 per cent fall in immunoreactive glucagon levels. These data demonstrate that (1) glycogenolysis is more sensitive than gluconeogenesis to the inhibitory effect of small increments in insulin concentrations, (2) gluconeogenesis could be suppressed by insulin but only at higher insulin concentrations, (3) this suppression of gluconeogenesis from alanine by insulin was due to an intrahepatic effect rather than an effect on the splanchnic extraction of alanine, and finally, (4) that insulin can suppress glucagon in the absence of hyperglycemia.     

Hyperglycemia decreases glucose uptake in type I diabetes

It has recently been postulated that hyperglycemia per se may contribute to insulin resistance in diabetes. To examine this possibility directly, we measured glucose uptake after 24 h of hyperglycemia (281 +/- 16 mg/dl) and normoglycemia (99 +/- 6 mg/dl) in 10 type I (insulin-dependent) diabetic patients (age 33 +/- 3 yr, relative body wt 102 +/- 3%) treated with continuous subcutaneous insulin infusion. Hyperglycemia was induced by an intravenous glucose infusion, whereas saline was administered during the control day. During both studies the patient received a similar diet and insulin dose. After hyper- and normoglycemia, a primed continuous infusion of insulin (40 mU X m-2 X min-1) was started, and plasma glucose was adjusted to and maintained at 142 +/- 2 and 140 +/- 2 mg/dl, respectively, during 60-160 min of insulin infusion. The rate of glucose uptake after hyperglycemia averaged 8.3 +/- 1.1 mg X kg-1 X min-1, which was lower than the rate after the normoglycemic period (10.1 +/- 1.2 mg X kg-1 X min-1, P less than .001). In conclusion, short-term hyperglycemia reduces glucose uptake in type I diabetic patients. Thus, part of the glucose or insulin resistance in these patients may be caused by hyperglycemia per se.     

Optimal insulin treatment in syngeneic islet transplantation

Insulin-induced normoglycemia has shown to have a beneficial effect on the outcome of pancreatic islets transplanted to diabetic recipients. The aim of the study was to identify the insulin treatment that can maximize its beneficial effect on islet transplants. Six groups of streptozotocin diabetic C57Bl/6 mice were transplanted (Tx) with 100 syngeneic islets, an insufficient beta cell mass to restore normoglycemia, and were treated with insulin as follows: group 1 (n = 9): from day 10 before Tx to day 14 after Tx; group 2 (n = 11): from day 6 before Tx to Tx day; group 3 (n = 11): from Tx day to day 6 after Tx; group 4 (n = 7): from Tx day to day 14 after Tx; group 5 (n = 8): from day 10 to day 24 after Tx; group 6 (n = 18): Tx mice were not treated with insulin. Sixty days after Tx, normoglycemia was achieved in 100% of mice in groups 1, 4, and 5, in 73% of mice in group 2, and in only 45% and 33% of mice in groups 3 and 6, respectively (p < 0.01). Intraperitoneal glucose tolerance, determined only in normoglycemic mice, was similar in groups 1, 2, 4, and normal controls. In contrast, normoglycemic mice from groups 3, 5, and 6, exposed to more severe and prolonged hyperglycemia after Tx, showed higher glucose values after glucose injection, suggesting that hyperglycemia had a long-lasting deleterious effect on transplanted beta cell function. The initially transplanted beta cell mass was maintained in the grafts of normoglycemic mice, but was severely reduced in hyperglycemic mice. Transplanted beta cell mass was similar in normoglycemic groups with normal or impaired glucose tolerance, indicating that impaired glucose tolerance was not due to reduced beta cell mass. In summary, the beneficial effect of insulin-induced normoglycemia on transplanted islets was maximal when insulin treatment was maintained the initial 14 days after transplantation. Exposure to sustained hyperglycemia initially after transplantation had a long-lasting deleterious effect on transplanted islets.     

Transient stimulatory effect of sustained hyperglucagonemia on splanchnic glucose production in normal and diabetic man.

Insulin can modulate glucagon-stimulated hepatic glucose production and is considered to be the major factor acting in vivo to exert a couterregulatory action to glucagon. The insulin-dependent diabetic, therefore, might be especially vulnerable to enhanced hepatic glucose production promoted by glucagon. To investigate this hypothesis, low-dose glucagon infusions were administered to normal and diabetic men to compare the effects of glucagon on net splanchnic glucose production (NSGP). Four normal and three insulin-dependent, ketosis-prone, hyperglycemic diabetic men (insulin withheld for 24 hours) underwent brachial-artery-hepatic-vein catheterization. Each received a 90-minute glucagon infusion at 5 ng/kg./min. Glucagon levels rose four-to-fivefold in both groups, plateauing at 300-600 pg./ml. In the normals, NSGP rose from 92+/-12 to 211+/-31 mg./min. at 15 minutes and returned to basal levels by 45 minutes. Insulin measured in the hepatic vein rose from 19+/-6 to 33+/-11 muU/.ml., while plasma glucose rose 17 mg./dl. In the insulin-dependent diabetics, NSGP rose from 78+/-24 to a peak of 221+/-33 mg./min. at 30 minutes and then fell sharply to 113+/-15 mg./min. at 60 minutes despite continuing hyperglucagonemia. Plasma glucose in the diabetics rose 21 mg./dl. These data suggest a mechanism that acts to rapidly diminish glucagon-induced hepatic glucose production in diabetic man but does not appear to be mediated by increased insulin secretion.     

Glucose tolerance in a Saharan nomad population--the Broayas, from the Toubou ethnic group.

Oral plucose tolerance was studied in the Toubou Broayas living in northeaster Niger. Mean fasting plasma level of glucose was 64 +/- 22 (S.D.) mg./100 ml. Two hours after oral administration of 100 gm. glucose, the level was 74 +/- 26 mg./100 ml. Plasma insulin levels were, respectively, 18 +/- 13 and 36 +/- 24 muU./ml. There was no sex difference. Older subjects had higher glucose levels and heavier females had higher insulin levels two hours after glucose administration. In six subjects (4 per cent) the plasma glucose level exceeded either 110 or 130 mg./100 ml. in the fasting state or after glucose administration, respectively, without, however, exceeding 150 mg./100 ml. in any of them. The low prevalence of glucose intolerance in this population is discussed with regard to their nutritional conditions (80 per cent carbohydrates) and their physical activity (nomadism). The Broaya group, in whom obesity is unknown, appears to be well adapted to its extreme environment.     

Maintenance of normoglycemia during cardiac surgery

We used the hyperinsulinemic normoglycemic clamp technique, i.e., infusion of insulin at a constant rate combined with dextrose titrated to clamp blood glucose at a specific level, to preserve normoglycemia during elective cardiac surgery. Ten nondiabetic and seven diabetic patients entered the clamp protocols. Perioperative glucose control was also assessed in 19 nondiabetic and 11 diabetic patients (control group) receiving a conventional insulin infusion sliding scale. In patients of the clamp group, a priming bolus of insulin (2 U) was started before the induction of anesthesia followed by infusions of insulin at 5 mU. kg(-1). min(-1) and of variable amounts of dextrose. Arterial blood glucose was measured every 5 min in the clamp group and every 20 min in the control group. Control of normoglycemia was defined as > or =95% of the glucose levels within 4.0-6.0 mmol/L. Glucose concentration was recorded before surgery, 15 min before cardiopulmonary bypass (CPB), during early and late CPB, and at sternal closure. Patients of the control group became progressively hyperglycemic during surgery (late CPB; nondiabetics, 9.0 +/- 3.2 mmol/L; diabetics, 10.1 +/- 3.6 mmol/L), whereas normoglycemia was achieved in the study group (late CPB; nondiabetics, 5.5 +/- 0.7 mmol/L; diabetics, 4.9 +/- 0.6 mmol/L; P < 0.05 versus control group). In conclusion, it seems that normal blood glucose concentration during open heart surgery can be reliably maintained in nondiabetic and diabetic patients by using the hyperinsulinemic normoglycemic clamp technique.     

Beta-cell death and mass in syngeneically transplanted islets exposed to short- and long-term hyperglycemia.

We studied the effects of hyperglycemia on beta-cell death and mass in syngeneically transplanted islets. Six groups of STZ-induced diabetic C57BL/6 mice were transplanted with 100 syngeneic islets, an insufficient beta-cell mass to restore normoglycemia. Groups 1, 2, and 3 remained hyperglycemic throughout the study. Groups 4, 5, and 6 were treated with insulin from day 7 before transplantation to day 10 after transplantation. After insulin discontinuation, group 6 mice achieved definitive normoglycemia. Grafts were harvested at 3 (groups 1 and 4), 10 (groups 2 and 5), and 30 (groups 3 and 6) days after transplantation. On day 3, the initially transplanted beta-cell mass (0.13 +/- 0.01 mg) was dramatically and similarly reduced in the hyperglycemic and insulin-treated groups (group 1: 0.048 +/- 0.002 mg; group 4: 0.046 +/- 0.007 mg; P < 0.001). Extensive islet necrosis (group 1: 30.7%; group 4: 26.8%) and increased beta-cell apoptosis (group 1: 0.30 +/- 0.05%; group 4: 0.42 +/- 0.07%) were found. On day 10, apoptosis remained increased in both hyperglycemic and insulin-treated mice (group 2: 0.44 +/- 0.09%; group 5: 0.48 +/- 0.08%) compared with normal pancreas (0.04 +/- 0.03%; P < 0.001). In contrast, on day 30, beta-cell apoptosis was increased in grafts exposed to sustained hyperglycemia (group 3: 0.37 +/- 0.03%) but not in normoglycemic mice (group 6: 0.12 +/- 0.02%); beta-cell mass was selectively reduced in islets exposed to hyperglycemia (group 3: 0.046 +/- 0.02 mg; group 6: 0.102 +/- 0.009 mg; P < 0.01). In summary, even in optimal conditions, approximately 60% of transplanted islet tissue was lost 3 days after syngeneic transplantation, and both apoptosis and necrosis contributed to beta-cell death. Increased apoptosis and reduced beta-cell mass were also found in islets exposed to chronic hyperglycemia, suggesting that sustained hyperglycemia increased apoptosis in transplanted beta-cells.     

The Effect of Chronic Dexamethasone-induced Hyperglycemia and Its Acute Treatment with Insulin on Brain Glucose and Glycogen Concentrations in Rats

Background: In the rat model of forebrain ischemia, long-term dexamethasone treatment is reported to cause hyperglycemia and worsen postischemic functional and histologic injury. This effect was assumed to result from glucose enhancement of intraischemic lactic acidosis within the brain. Short-term insulin therapy restored normoglycemia but did not return histologic injury completely to baseline values. Using a nonischemic rat model, the current study attempted to identify a metabolic basis for such outcome data.

Methods: Fifty-eight halothane-anesthetized (1.3% inspired) Sprague-Dawley rats were assigned randomly to be administered either no treatment (N = 18) or 2 mg/kg intraperitoneal dexamethasone (N = 40). The latter were administered dexamethasone 3 h before the study only (N = 8) or for 3 h before the study plus daily for 1 day (N = 8), 2 days (N = 8), or 4 days (N = 16). Of the rats treated with dexamethasone for 4 days, one half (N = 8) were administered an insulin-containing saline infusion subsequently to restore normoglycemia short-term. All other rats (N = 50) were administered an infusion of saline without insulin. Plasma glucose was quantified, and brains were excised after in situ freezing. Brain glucose and glycogen concentrations were measured using enzymatic fluorometric analyses.

Results: After 4 days of dexamethasone treatment, plasma glucose was 159% greater than in rats administered placebo (i.e., 22.01 +/- 4.66 vs. 8.51 +/- 1.65 [mu]mol/ml; mean +/- SD;P < 0.0001). Brain glucose concentrations increased parallel to plasma glucose. An insulin infusion for 27 +/- 5 min restored normoglycemia but resulted in a brain-to-plasma glucose ratio that was 32% greater than baseline values (P < 0.01). Neither dexamethasone nor the combination of dexamethasone plus insulin affected brain glycogen concentrations.     

The effect of chronic dexamethasone-induced hyperglycemia and its acute treatment with insulin on brain glucose and glycogen concentrations in rats

BACKGROUND: In the rat model of forebrain ischemia, long-term dexamethasone treatment is reported to cause hyperglycemia and worsen postischemic functional and histologic injury. This effect was assumed to result from glucose enhancement of intraischemic lactic acidosis within the brain. Short-term insulin therapy restored normoglycemia but did not return histologic injury completely to baseline values. Using a nonischemic rat model, the current study attempted to identify a metabolic basis for such outcome data. METHODS: Fifty-eight halothane-anesthetized (1.3% inspired) Sprague-Dawley rats were assigned randomly to be administered either no treatment (N = 18) or 2 mg/kg intraperitoneal dexamethasone (N = 40). The latter were administered dexamethasone 3 h before the study only (N = 8) or for 3 h before the study plus daily for 1 day (N = 8), 2 days (N = 8), or 4 days (N = 16). Of the rats treated with dexamethasone for 4 days, one half (N = 8) were administered an insulin-containing saline infusion subsequently to restore normoglycemia short-term. All other rats (N = 50) were administered an infusion of saline without insulin. Plasma glucose was quantified, and brains were excised after in situ freezing. Brain glucose and glycogen concentrations were measured using enzymatic fluorometric analyses. RESULTS: After 4 days of dexamethasone treatment, plasma glucose was 159% greater than in rats administered placebo (i.e., 22.01 +/- 4.66 vs. 8.51 +/- 1.65 micromol/ml; mean +/- SD; P < 0.0001). Brain glucose concentrations increased parallel to plasma glucose. An insulin infusion for 27 +/- 5 min restored normoglycemia but resulted in a brain-to-plasma glucose ratio that was 32% greater than baseline values (P < 0.01). Neither dexamethasone nor the combination of dexamethasone plus insulin affected brain glycogen concentrations. CONCLUSIONS: In a nonischemic rat model, dexamethasone alone had no independent effect on the brain-to-plasma glucose ratio. However, short-term insulin therapy caused a dysequilibrium between plasma and brain glucose, resulting in an underestimation of brain glucose concentrations when normoglycemia was restored. The dysequilibrium likely was caused by the rapid rate of glucose reduction. The magnitude of the effect may account for the failure of insulin to reverse dexamethasone enhancement of neurologic injury completely in a previous report that used the rat model of forebrain ischemia.     

Autotransplantation of Pancreatic Fragments to the Portal Vein and Spleen of Totally Pancreatectomized Dogs: A Comparative Evaluation

Forty-nine dogs were made diabetic by total pancreatectomy. Fifteen untreated pancreatectomized animals survived a mean (+/-S.E.) of 7.0 +/- 1.1 days with a mean (+/-S.E.) plasma glucose level of 402 +/- 26 mg/100 ml before death. The pancreata of 32 dogs were distended with cold (4 degrees ) Hanks' solution, minced, digested with collagenase (600 U/ml tissue) for 15-25 minutes, and autotransplanted either into the splenic artery (three dogs), directly into the splenic pulp (21 dogs), or into the portal vein (ten dogs). Tissue infusion into the splenic artery resulted in infarction and persistent hyperglycemia. Direct implantation into the splenic pulp of tissue digested for 15, 20 and 25 minutes resulted in permanent normoglycemia (fasting plasma glucose < 150 mg/100 ml) in 7 of 8, 7 of 7, and 6 of 6 dogs respectively. Glucose tolerance test mean (+/-S.E.) K values (% decline of plasma glucose concentration/minute) in these groups two weeks after transplantation were 1.20 +/- 0.20%, 1.60 +/- 0.25 and 0.70 0.08% respectively, indicating that 20 minutes digestion was best for intrasplenic transplantation. Tissue prepared in the optimal manner (20 minutes digestion) and embolized into the liver resulted in normoglycemia in three of eight dogs, and a mean (+/-S.E.) K value of 0.77 +/- 0.10%. Both dogs receiving tissue dispersed for 25 minutes into the portal vein remained hyperglycemic. In the dogs subjected to intraportal transplantation, portal pressure rose from a mean (+/-S.E.) of 6.5 +/- 0.6 cm H(2)O before to 21.9 +/- 2.2 cm H(2)O immediately after tissue embolization, but declined to 6.5 +/- 1.0 cm H(2)O by ten weeks in animals becoming normoglycemic. We conclude that in dogs direct implantation of pancreatic tissue into the splenic pulp is superior to embolization into the portal vein or splenic artery because the splenic circulation is not compromized, portal hypertension is obviated, and glucose metabolism is best controlled as judged by glucose tolerance test K values.     

Acetylsalicyclic acid restores acute insulin response reduced by furosemide in man.

Prostaglandin E (PGE) infusion in normal man inhibits the acute insulin response to glucose. In order to determine whether endogenously released PGE might also inhibit insulin secretion, glucose-stimulated insulin responses were investigated in normal volunteers after furosemide (40 mg i.v.), a stimulator of endogenous PGE synthesis. Acute insulin response to glucose (20 g i.v.) was significantly reduced by furosemide (response before furosemide: 36 +/- 5 muU/ml; after furosemide: 26 +/- 5 muU/ml, m +/- SE, mean change 3--10 min, N = 8, P less than 0.01), whereas glucose disappearance rates were not modified after furosemide. Infusion of lysine acetylsalicylate (LAS), an inhibitor of endogenous PGE synthesis, completely reversed the inhibitory effect of furosemide on insulin secretion and also augmented acute insulin response to glucose (response before furosemide + LAS: 41 +/- 6 muU/ml; during furosemide + LAS: 50 +/- 7 muU/ml, N = 10, P less than 0.02). This effect was associated with an increase in glucose disappearance rates (P less than 0.05). These findings demonstrate that (1) furosemide inhibits glucose-induced acute insulin responses and (2) LAS completely reverses the inhibitory effect of furosemide and also accelerates glucose disposal. It is suggested that furosemide acts via the release of endogenous PGEs, which are known to inhibit insulin responses in man.     

Variation in the disappearance of unlabeled insulin from plasma: studies with portal and peripheral infusions.

One hundred and thirty brief infusions of unlabeled insulin were given to 75 unanesthetized nondiabetic human beings. The patients were examined (1) by different doses of insulin (5--50 muU/kg), (2) by intraportal and peripheral infusion, (3) in the morning and in the afternoon, and (4) during normoglycemia and moderate, steady hyperglycemia. After intraportal infusion of insulin, the non-steady state plasma clearance rate (ml min(-1)kg(-1) was lower the larger the dose (decreased about 50% by a 10-fold increase in insulin dose) and lower at hyper- than at normoglycemia (decreased about 30% after small insulin doses). It was also lower the higher the relative body weight, but this correlation was weak. After peripheral insulin infusion, none of the above relationships was demonstrated. Regardless of the route of insulin infusion, plasma clearance rate did not vary with fasting plasma insulin concentration, time of day, insulin sensitivity, or glucose tolerance. We conclude that the liver modifies the distribution and removal of pancreatically released insulin in response to acute increases in insulin or glucose. Otherwise the plasma clearance rate of insulin showed a notable lack of relationship with common indexes of metabolism and with insulin action.     

Investigation of insulin sensitivity in treated subjects with ketosis-prone diabetes mellitus.

Two similar intravenous infucion techniques have been utilized to investigate insulin sensitivity in young subjects with recent-onset ketosis-prone diabetes mellitus. All subjects presented initially with mild to moderately severe ketoacidosis and had been treated with daily insulin therapy for two to eight weeks at the time of study. Six diabetics and 10 normal subjects (group A) received intravenous infusions of glucose (6 mg./kg./min), insulin (80 mU./min.) for 150 minutes. Steady-state plasma glucose (SSPG) and insulin levels (SSPI) were reached by 90 minutes and maintained through the end of the study. As all subjects achieve simolas SSPI while simultaneously receiving similar glucose loads, the SSPG can be used to measure individual insulin sensitivity. Under these conditions the diabetics in group A had a mean SSPG (+/-S.E.) of 99+/-26 mg./100ml., which was not different from the level of 98 +/-14mg./100 ml. for their control subjects. Six diabetics and six normal subjects (group B) received infusions of only glucose (6 mg./kg./min.) and insulin (80 mU./min.). Similar SSPI levels were attained in both the diabetic and control subjects, and their mean SSPG (+/-S.E.) levels were not significantly different (83+/- 13 vs. 61 +/-6 mg./100 ml.). One diabetic in group A and two diabetics in group B had SSPG levels above the highest values measured in their control groups. However, all three had markedly elevated fasting plasma glucose levels on the day of study. In contrast, nine well-controlled diabetics had normal insulin sensitivity. These results suggest that well-controlled subjects with ketosis-prone diabetes mellitus have normal sensitivity to insulin.     

Comparison of insulin secretory patterns in obese nondiabetic LA/N-cp and obese diabetic SHR/N-cp rats. Role of hyperglycemia

Obese diabetic SHR/N-(cp/cp) rats are a genetic model for non-insulin-dependent diabetes mellitus. When SHR/N-cp rats are overtly diabetic, they are hyperinsulinemic and hyperglycemic in the fed state when consuming commercial chow or semipurified high-carbohydrate diets. Obese SHR/N-cp rats were hyperinsulinemic by 4 wk of age, although hyperglycemia did not appear until 3-4 wk later and was exacerbated by a high-sucrose diet (mean +/- SE 1488 +/- 238 microU/ml insulin and 425 +/- 51 mg/dl glucose). The control SHR/N-cp rats (+/?) on the sucrose diet remained lean and normoglycemic. The obese diabetic SHR/N-cp rats showed three alterations in pancreas perfusion data (not present in control rats): 1) paradoxically high insulin secretion at low glucose levels (2.5 mM), 2) secretion of insulin in response to arginine (10 mM) in the absence of glucose, and 3) impaired response of insulin secretion to high glucose (16.7 mM). To determine whether hyperglycemia was responsible for the abnormalities of insulin secretion, perfusion studies were conducted in obese nondiabetic LA/N-cp rats and compared with the SHR/N-cp rats. The obese LA/N-cp rats resembled the corpulent SHR/N-cp rats in every way, except that they were normoglycemic on the sucrose diet. The obese LA/N-cp rats had two of the three alterations in insulin secretion shown by obese SHR/N-cp rats, lacking only the impaired response to high glucose, suggesting that hyperglycemia was required for that defect to occur.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cerebral taurine transport is increased during streptozocin-induced diabetes in rats.

Taurine is a cerebral osmolyte whose intracellular content changes in parallel with plasma osmolality. We conducted experiments to assess whether cerebral taurine transport is modified during chronic hyperglycemia. Rats with STZ-induced diabetes were studied after 1 wk of sustained hyperglycemia. Cerebral taurine uptake in synaptosomes (metabolically active nerve terminal vesicles) was measured using a rapid filtration technique. The synaptosomes were isolated by homogenization of the brain and purification on discontinuous Ficoll gradients (n = 8 synaptosome preparations). Diabetic rats (n = 13) displayed a 15-25% increase in synaptosomal taurine uptake compared with normoglycemic control animals (n = 12) at all time points assayed between 5 and 120 min. Thus, after a 30-min incubation, cerebral taurine uptake increased from a control level of 3.53 +/- 0.23 to 4.10 +/- 0.24 mumol/mg protein (n = 10) in hyperglycemic rats, P less than 0.03. The magnitude of the plasma-to-brain cell taurine gradient was unchanged in diabetic animals. The intrasynaptosomal taurine concentration (approximately 2 microM) and taurine efflux from the synaptosomes were no different in hyperglycemic versus control rats; efflux amounted to less than 2.5% of the uptake value at corresponding time points. Maximal brain taurine uptake under both control and experimental hyperglycemic conditions required the presence of external Na+ and Cl-. Synaptosomal taurine transport was reduced by competing beta-amino acids such as beta-alanine, beta-aminoisobutyric acid, and hypotaurine (P less than 0.01). Addition of oubain and the anionic binding site inhibitors, 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid and 4,4'diisothio-cyanatostilbene-2,2'-disulfonic acid, also decreased cerebral taurine uptake under normoglycemic and hyperglycemic conditions (P less than 0.01). The increased synaptosomal taurine uptake by diabetic rats was not a result of generalized membrane dysfunction because glycine transport was not elevated in hyperglycemic rats. The enhanced transport rate was attributable to a 35 and 81% increase in the Vmax of the high- and low-affinity taurine transporters, respectively (P less than 0.01), without significant change in the Km of the carrier systems. Treatment of hyperglycemic rats (n = 5) with ultra-long-acting insulin to normalize the serum glucose concentration restored synaptosomal taurine uptake to the level observed in normoglycemic controls. The effect of insulin was attributable to correction of hyperglycemia, because addition of insulin (500 mU/ml) to the in vitro assay system did not alter synaptosomal taurine uptake.(ABSTRACT TRUNCATED AT 400 WORDS)     

Loss of insulin response to ingested amino acids after jejunoileal bypass surgery for morbid obesity

Amino acid tolerance tests were performed before and after jejunoileal bypass surgery for morbid obesity to determine whether an enteric factor(s) originating in the bypassed jejunum and/or ileum potentiates the insulin response to oral nitrogen loading. Preoperatively a 30-gm. mixture of amino acids given orally evoked a larger peak insulin than an intravenous load yielding comparable plasma amino acid elevations (82 +/- 17 muU./ml versus 38 +/- 8 muU./ml., p less than 0.05). Four months after operation, basal insulin concentrations were 46 per cent (p less than 0.001) of preoperative values. After surgery the response to intravenous amino acids was preserved when expressed as percentage increase above basal. In contrast, the peak increment and the percentage increase in insulin secretion after 30-gm. oral amino acid loading was significantly blunted (p less than 0.005). A smaller amino acid load (16.5 gm.) was given preoperatively to duplicate the plasma amino acid elevations seen postoperatively with the 30-gm. mixture given by mouth. The insulin response postoperatively was still significantly lower (167 +/- 33 per cent versus 98 +/- 16 per cent, p less than 0.05). After various explanations for the diminished postoperative insulin release following oral amino acid ingestion are considered, the results are best explained by the loss of an enteric insulinotrophic factor(s) normally released by the bypassed portions of jejunum or ileum in response to ingested protein.     

Counteraction of type 1 diabetic alterations by engineering skeletal muscle to produce insulin: insights from transgenic mice

Insulin replacement therapy in type 1 diabetes is imperfect because proper glycemic control is not always achieved. Most patients develop microvascular, macrovascular, and neurological complications, which increase with the degree of hyperglycemia. Engineered muscle cells continuously secreting basal levels of insulin might be used to improve the efficacy of insulin treatment. Here we examined the control of glucose homeostasis in healthy and diabetic transgenic mice constitutively expressing mature human insulin in skeletal muscle. Fed transgenic mice were normoglycemic and normoinsulinemic and, after an intraperitoneal glucose tolerance test, showed increased glucose disposal. When treated with streptozotocin (STZ), transgenic mice showed increased insulinemia and reduced hyperglycemia when fed and normoglycemia and normoinsulinemia when fasted. Injection of low doses of soluble insulin restored normoglycemia in fed STZ-treated transgenic mice, while STZ-treated controls remained highly hyperglycemic, indicating that diabetic transgenic mice were more sensitive to the hypoglycemic effects of insulin. Furthermore, STZ-treated transgenic mice presented normalization of both skeletal muscle and liver glucose metabolism. These results indicate that skeletal muscle may be a key target tissue for insulin production and suggest that muscle cells secreting basal levels of insulin, in conjunction with insulin therapy, may permit tight regulation of glycemia.     

Autotransplantation of pancreatic islets without separation of exocrine and endocrine tissue in totally pancreatectomized dogs.

The aims of this study were to determine whether diabetes could be ameliorated in dogs by autotransplantation of pancreatic fragments to the spleen and to determine the optimal time of collagenase digestion for pancreatic tissue dispersal. Forty-eight dogs were made diabetic by total pancreatectomy. Fifteen dogs not further treated survived 7.0+/-1.1 (SE) days with a mean plasma glucose of 401+/-5 (SE) mg/100 ml 2 days after pancreatectomy. The pancreases of 33 dogs were distended with Hanks' solution, minced, digested with collagenase (600 microns/ml of tissue), for 0 to 25 minutes, and autotransplanted to the splenic pulp. The incidence of permanent normoglycemia (fasting plasma glucose less than 150 mg/100 ml) and the K value of glucose tolerance tests (GTT) performed 2 and 10 weeks after transplant were determined in experimental groups divided according to the length of collagenase digestion. All five dogs receiving undigested tissue remained hyperglycemic. One of seven dogs receiving tissue digested for 10 minutes became normoglycemic. In contrast, seven of eight, seven of seven, and six of six dogs receiving tissue digested for 15, 20, and 25 minutes, respectively, became normoglycemic (followed for 6 months). K values at 2 weeks were 1.20+/-1.19 (SE)% 1.60+/-0.25 (SE)%, and 0.78+/-0.08 (SE)% in the normolgycemic dogs of the 15, 20, and 25 minute digestion groups, respectively. The K value of normal dogs was 3.30+/-0.27 (SE)%. The glucose tolerance curves of the 20 minute group at 2 and 10 weeks most nearly approximated the curves of normal dogs. K values improved in all recipient dogs. Diabetes recurred immediately and death occurred at a mean of 4.8+/-1.5 days in 12 recipient dogs following splenectomy. We conclude that pancreatic fragments can be successfully autotransplanted to the spleen without separation of endocrine and exocrine tissue and that 20 minutes is the optimal period of collagenase digestion for tissue preparation.