Enhanced hepatic insulin sensitivity, but peripheral insulin resistance in patients with type 1 (insulin-dependent) diabetes

The Impact of Body Mass Index, Residual Beta Cell Function and Estimated Glucose Disposal Rate on the Development of Double Diabetes and Microvascular Complications in Patients With Type 1 Diabetes Mellitus

Background The clinical impact of body mass index (BMI), residual beta cell function and estimated glucose disposal rate (eGDR) in the development of double diabetes (DD) and microvascular complications are largely unknown. We aimed to assess whether BMI, residual beta cell function measured by plasma "C" peptide and insulin resistance measured by eGDR have any impact on the development of DD and microvascular complications in patients with type 1 diabetes mellitus (T1DM). Methods It is a cross-sectional observational study involving 113 T1DM patients of more than five years duration who were classified into two groups: normal BMI (18.5-22.9 kg/m2) and overweight/obese group (≥ 23kg/m2) based on Asian BMI classification. Based on their eGDR values, they were grouped into four categories: ≥ 8, 6-7.99, 4-5.99, and < 4 mg/kg/min. The prevalence of DD based on eGDR values was determined. Their BMI and different eGDR categories were compared with the prevalence of diabetic retinopathy and nephropathy and their odds ratio (OR) was calculated. Results The median and interquartile range (IQR) of the eGDR of the overweight/obese group was significantly lower than the normal BMI group (5.3 [3.96-8.15] vs 8.72 [6.50-9.77 mg/kg/min], p < 0.001). The prevalence of DD in the overweight/obese T1DM group and normal BMI group was 75% and 33.3% respectively. The OR of retinopathy and nephropathy in the overweight/obese group was 3.28 (p = 0.007) and 3.01 (p = 0.015) respectively when compared to the normal BMI group. The OR of retinopathy and nephropathy in T1DM patients with eGDR < 4 mg/kg/min was 17.13 (p = 0.001) and 18.5 (p = 0.001) respectively. The lower the eGDR values, the higher the prevalence of retinopathy and nephropathy regardless of HbA1c levels. Conclusion As overweight and obesity are increasingly becoming more prevalent in T1DM, the eGDR will better predict the development of DD and microvascular complications irrespective of HbA1c levels. It is more useful as a variable and easily inducted into routine clinical practice. However, residual beta cell function was not useful in predicting the development of microvascular complications.

Metabolic determinants of NAFLD in adults with type 1 diabetes

AIM

To assess the main metabolic determinants of non-alcoholic fatty liver disease (NAFLD) in adult patients with type 1 diabetes (T1D).

METHODS

115 patients with T1D were divided into 4 groups according to NAFLD grade. NAFLD was diagnosed via transient elastography when CAP > 233 dB/m. Body composition was evaluated by Inbody720, Biospace. Serum lipids, liver enzymes, uric acid, creatinine, hsCRP and HbA1c were evaluated at fasting.

RESULTS

The overall prevalence of NAFLD was 47% (n = 54). In the subgroup with BMI > 25 kg/m² NAFLD prevalence was 66%; and positive family history of type 2 diabetes brought the risk up to 76%. 37% of the lean individuals also had NAFLD. HbA1c > 7% doubled the risk of NAFLD. Waist circumference > 82.5 cm was independently related to NAFLD, accounting for 24% of its variation in females. Accumulation of two and three metabolic syndrome (MetS) components, besides hyperglycemia, increased the risk of NAFLD by 14% (p < 0.0001) and 6% (p = 0.024), respectively. Lean NAFLD correlated with total insulin dose; NAFLD in overweight T1D patients correlated with triglycerides.

CONCLUSIONS

NAFLD is highly prevalent in adults with T1D and obesity or other metabolic derangements and might be independently related to poor long-term glycemic control and waist circumference in females.

Specific Nuclear Magnetic Resonance Lipoprotein Subclass Profiles and Central Arterial Stiffness in Type 1 Diabetes Mellitus: A Case Control Study

BACKGROUND

Dyslipidemia has been associated with vascular complications of type 1 diabetes mellitus (T1DM). We examined the proton nuclear magnetic resonance (NMR)-assessed lipoprotein subclass profiles in subjects with T1DM compared with those of healthy subjects and assessed the potential relationship of these profiles with arterial stiffness.

METHODS

Eighty-four participants with T1DM of at least 10 years duration and no clinical cardiovascular disease (age: 35-65 years; 50% men) and 42 healthy participants were evaluated for: (1) clinical and anthropometric data (including classical cardiovascular risk factors), (2) insulin sensitivity by estimated glucose disposal rate, (3) microvascular complications, (4) NMR-assessed lipoprotein subclass profile, and (5) arterial stiffness (aortic pulse wave velocity).

RESULTS

Participants with T1DM had an apparently better conventional lipid profile than healthy participants, but with significant differences in NMR-assessed lipoprotein profiles such as higher triglyceride content of low-density lipoprotein (LDL) and high-density lipoprotein (HDL). In healthy participants, arterial stiffness was associated with NMR-based LDL subclasses. By contrast, in T1DM participants, arterial stiffness was independently associated mainly with NMR-based very-low-density lipoprotein (VLDL) subclasses: positively with total VLDL particles (and subclasses) and VLDL triglyceride content, and negatively with LDL and HDL particle sizes. These results were maintained after adjustments for classical cardiovascular risk factors.

CONCLUSIONS

Subjects with T1DM, while having an apparently better conventional lipid profile than healthy controls, presented significant alterations in their NMR-assessed lipoprotein profile. The association between arterial stiffness and NMR-assessed lipoprotein profiles also differed in both groups. These results support a potential role of the identified differences in the residual cardiovascular risk in T1DM.

Insulin resistance in patients with type 1 diabetes assessed by glucose clamp studies: systematic review and meta-analysis

OBJECTIVE

The aim of this study was to perform a systematic review and meta-analysis on insulin resistance in adult patients with type 1 diabetes mellitus compared to healthy controls, assessed by hyperinsulinemic euglycemic clamp studies.

DESIGN AND METHODS

We conducted a systematic search of publications using PubMed, EMBASE, Web of Science and COCHRANE Library. Hyperinsulinemic euglycemic clamp studies comparing adult patients with type 1 diabetes mellitus to healthy controls were eligible. Primary outcome measures were pooled mean differences of insulin sensitivity of endogenous glucose production (EGP), of glucose uptake and of lipolysis. We estimated mean (standardized) differences and 95% CIs using random effects meta-analysis.

RESULTS

We included 38 publications in this meta-analysis. The weighed mean differences in EGP during hyperinsulinemia between patients and controls was 0.88 (95% CI: 0.47, 1.29) in the basal state and 0.52 (95% CI: 0.09, 0.95) in insulin stimulated conditions, indicating decreased hepatic insulin sensitivity in patients. Insulin sensitivity of glucose uptake was either reported as M value (M), glucose infusion rate (GIR), glucose disposal rate (GDR) or metabolic clearance rate (MCR). Weighed mean differences were similar for M -3.98 (95% CI: -4.68, -3.29) and GIR -4.61 (95% CI: -5.86, -3.53). Weighed mean difference for GDR was -2.43 (95% CI: -3.03, -1.83) and -3.29 (95% CI: -5.37, -1.22) for MCR, indicating decreased peripheral insulin sensitivity in patients. Insulin mediated inhibition of lipolysis was decreased in patients, reflected by increased non-esterified fatty acid levels.

CONCLUSIONS

Insulin resistance is a prominent feature of patients with type 1 diabetes mellitus and involves hepatic, peripheral and adipose tissues.

Postprandial and fasting hepatic glucose fluxes in long-standing type 1 diabetes

OBJECTIVE

Intravenous insulin infusion partly improves liver glucose fluxes in type 1 diabetes (T1D). This study tests the hypothesis that continuous subcutaneous insulin infusion (CSII) normalizes hepatic glycogen metabolism.

RESEARCH DESIGN AND METHODS

T1D with poor glycemic control (T1Dp; HbA(1c): 8.5 ± 0.4%), T1D with improved glycemic control on CSII (T1Di; 7.0 ± 0.3%), and healthy humans (control subjects [CON]; 5.2 ± 0.4%) were studied. Net hepatic glycogen synthesis and glycogenolysis were measured with in vivo (13)C magnetic resonance spectroscopy. Endogenous glucose production (EGP) and gluconeogenesis (GNG) were assessed with [6,6-(2)H(2)]glucose, glycogen phosphorylase (GP) flux, and gluconeogenic fluxes with (2)H(2)O/paracetamol.

RESULTS

When compared with CON, net glycogen synthesis was 70% lower in T1Dp (P = 0.038) but not different in T1Di. During fasting, T1Dp had 25 and 42% higher EGP than T1Di (P = 0.004) and CON (P < 0.001; T1Di vs. CON: P = NS). GNG was 74 and 67% higher in T1Dp than in T1Di (P = 0.002) and CON (P = 0.001). In T1Dp, GP flux (7.0 ± 1.6 μmol ⋅ kg(-1) ⋅ min(-1)) was twofold higher than net glycogenolysis, but comparable in T1Di and CON (3.7 ± 0.8 and 4.9 ± 1.0 μmol ⋅ kg(-1) ⋅ min(-1)). Thus T1Dp exhibited glycogen cycling (3.5 ± 2.0 μmol ⋅ kg(-1) ⋅ min(-1)), which accounted for 47% of GP flux.

CONCLUSIONS

Poorly controlled T1D not only exhibits augmented fasting gluconeogenesis but also increased glycogen cycling. Intensified subcutaneous insulin treatment restores these abnormalities, indicating that hepatic glucose metabolism is not irreversibly altered even in long-standing T1D.

Chronic peripheral hyperinsulinemia in type 1 diabetic patients after successful combined pancreas-kidney transplantation does not affect ectopic lipid accumulation in skeletal muscle and liver

OBJECTIVE

So far it is unclear whether chronic peripheral hyperinsulinemia per se might contribute to ectopic lipid accumulation and consequently insulin resistance. We investigated the effects of systemic instead of portal insulin release in type 1 diabetic patients after successful pancreas-kidney transplantation (PKT) with systemic venous drainage on the intracellular lipid content in liver and soleus muscle, endogenous glucose production (EGP), and insulin sensitivity.

RESEARCH DESIGN AND METHODS

In nine PKT patients and nine matching nondiabetic control subjects, intrahepatocellular lipids (IHCLs) and intramyocellular lipids (IMCLs) were measured using (1)H nuclear magnetic resonance spectroscopy. Fasting EGP was measured using d-[6,6-(2)H(2)]glucose tracer dilution. A 3-h 75-g oral glucose tolerance test (OGTT) allowed us to assess kinetics of glucose, free fatty acids, insulin, and C-peptide concentrations in plasma and to calculate the clamp-like index (CLIX) for insulin sensitivity and the hepatic insulin resistance (HIR) index.

RESULTS

The PKT patients displayed approximately twofold increased fasting insulin (20 +/- 6 vs. 9 +/- 3 microU/ml; P < 0.0002) compared with that in nondiabetic control subjects and approximately 10% increased fasting glucose (P < 0.02) concentrations, but during the OGTT areas under the concentration curves of C-peptide and insulin were similar. IHCL (PKT, 2.9 +/- 2.5%; nondiabetic control subjects, 4.4 +/- 6.6%), IMCL (PKT, 1.0 +/- 0.4%; nondiabetic control subjects, 1.0 +/- 0.5%), CLIX (PKT, 8 +/- 2; nondiabetic control subjects, 7 +/- 3), HIR (PKT, 25.6 +/- 13.2; nondiabetic control subjects, 35.6 +/- 20 [mg * min(-1) * kg(-1)] x [microU/ml]), and EGP (PKT, 1.6 +/- 0.2; nondiabetic control subjects, 1.7 +/- 0.2 mg * min(-1) * kg(-1)) were comparable between PKT patients and nondiabetic control subjects. IHCL was negatively correlated with CLIX in all participants (r = -0.55; P < 0.04).

CONCLUSIONS

Despite fasting peripheral hyperinsulinemia because of systemic venous drainage, type 1 diabetic patients after PKT show similar IHCL, IMCL, insulin sensitivity, and fasting EGP in comparison with nondiabetic control subjects. These results suggest that systemic hyperinsulinemia per se does not cause ectopic lipid accumulation in liver and skeletal muscle.

Differential effects of insulin deprivation and systemic insulin treatment on plasma protein synthesis in type 1 diabetic people

It remains to be determined whether systemic insulin replacement normalizes synthesis rates of different plasma proteins and whether there are differential effects on various plasma proteins. We tested a hypothesis that insulin deprivation differentially affects individual plasma protein synthesis and that systemic insulin treatment may not normalize synthesis of all plasma proteins. We measured synthesis rates of 41 plasma proteins in seven each of type 1 diabetic (T1DM) and nondiabetic participants (ND) using [ring-(13)C(6)]phenylalanine as a tracer. T1DM were studied while on chronic insulin treatment and during 8 h insulin deprivation. Insulin treatment normalized glucose levels, but plasma insulin levels were higher during insulin treatment than during insulin deprivation in T1DM and ND. Individual plasma proteins were purified by affinity chromatography and two-dimensional gel electrophoresis. Only 41 protein gel spots from over 300 were chosen based on their protein homogeneity. Insulin deprivation and hyperglycemia either significantly increased (n = 12) or decreased (n = 12) synthesis rates of 24 of 41 plasma proteins in T1DM compared with ND. Insulin treatment normalized synthesis rates of 13 of these 24 proteins, which were altered during insulin deprivation. However, insulin treatment significantly altered the synthesis of 14 additional proteins. In conclusion, acute insulin deprivation caused both a decrease and increase in synthesis rates of many plasma proteins with various functions. Moreover, chronic systemic insulin treatment not only did not normalize synthesis of all plasma proteins but also altered synthesis of several additional proteins that were unaltered during insulin deprivation.

Contrasting insulin sensitivity of endogenous glucose production rate in subjects with hepatocyte nuclear factor-1beta and -1alpha mutations

Heterozygous mutations in the transcription factors hepatocyte nuclear factor (HNF)-1alpha and -1beta result in MODY (maturity-onset diabetes of the young). Despite structural similarity between HNF-1alpha and -1beta, HNF-1beta mutation carriers have hyperinsulinemia, whereas HNF-1alpha mutation carriers have normal or reduced insulin concentrations. We examined whether HNF-1beta mutation carriers are insulin resistant. The endogenous glucose production rate and rate of glucose uptake were measured with a two-step, low-dose (0.3 mU . kg(-1) . min(-1)) and high-dose (1.5 mU . kg(-1) . min(-1)) hyperinsulinemic-euglycemic clamp, with an infusion of [6,6-(2)H(2)]glucose, in six subjects with HNF-1alpha mutations, six subjects with HNF-1beta mutations, and six control subjects, matched for age, sex, and BMI. Endogenous glucose production rate was not suppressed by low-dose insulin in HNF-1beta subjects but was suppressed by 89% in HNF-1alpha subjects (P = 0.004) and 80% in control subjects (P < 0.001). Insulin-stimulated glucose uptake and suppression of lipolysis were similar in all groups at low- and high-dose insulin. Subjects with HNF-1beta mutations have reduced insulin sensitivity of endogenous glucose production but normal peripheral insulin sensitivity. This is likely to reflect reduced action of HNF-1beta in the liver and possibly the kidney. This may be mediated through regulation by HNF-1beta of the key gluconeogenic enzymes glucose-6-phosphatase or PEPCK.

Reduced intrahepatic fat content is associated with increased whole-body lipid oxidation in patients with type 1 diabetes

AIMS/HYPOTHESIS

Insulin resistance may be associated with ectopic fat accumulation potentially determined by reduced lipid oxidation. In patients with type 1 diabetes peripheral insulin resistance is associated with higher intramyocellular lipid content. We assessed whether these patients are also characterised by intrahepatic fat accumulation and abnormal fat oxidation.

METHODS

Nineteen patients with type 1 diabetes (6 women, 13 men, age 35+/-7 years, BMI 23+/-3 kg/m2), HbA1c 8.7+/-1.4%) and 19 healthy matched individuals were studied by (1) euglycaemic-hyperinsulinaemic clamp combined with [6,6-2H2]glucose infusion to assess whole-body glucose metabolism; (2) indirect calorimetry to assess glucose and lipid oxidation; and (3) localised 1H-magnetic resonance spectroscopy of the liver to assess intrahepatic fat content.

RESULTS

Patients with type 1 diabetes showed a reduced insulin-stimulated metabolic clearance rate of glucose (4.3+/-1.3 ml kg(-1) min(-1)) in comparison with normal subjects (6.0+/-1.6 ml kg(-1) min(-1); p<0.001). Endogenous glucose production was higher in diabetic patients (p=0.001) and its suppression was impaired during insulin administration (66+/-30 vs 92+/-8%; p=0.047) in comparison with normal subjects. Plasma glucagon concentrations were not different between groups. The estimated hepatic insulin concentration was lower in diabetic patients than in normal subjects (p<0.05), as was the intrahepatic fat content (1.5+/-0.7% and 2.2+/-1.0% respectively; p<0.03), the latter in association with a reduced respiratory quotient (0.74+/-0.05 vs 0.84+/-0.06; p=0.01) and increased fasting lipid oxidation (1.5+/-0.5 vs 0.8+/-0.4 mg kg(-1) min(-1); p<0.01).

CONCLUSIONS/INTERPRETATION

In patients with type 1 diabetes, insulin resistance was not associated with increased intrahepatic fat accumulation. In fact, diabetic patients had reduced intrahepatic fat content, which was associated with increased fasting lipid oxidation. The unbalanced hepatic glucagon and insulin concentrations affecting patients with type 1 diabetes may be involved in this abnormality of intrahepatic lipid metabolism.

Hepatic glycogen metabolism in type 1 diabetes after long-term near normoglycemia

We tested the impact of long-term near normoglycemia (HbA(1c) <7% for >1 year) on glycogen metabolism in seven type 1 diabetic and seven matched nondiabetic subjects after a mixed meal. Glycemic profiles (6.2 +/- 0.10 vs. 5.9 +/- 0.07 mmol/l; P < 0.05) of diabetic patients were approximated to that of nondiabetic subjects by variable insulin infusion. Rates of hepatic glycogen synthesis and breakdown were calculated from the glycogen concentration time curves between 7:30 P.M. and 8:00 A.M. using in vivo (13)C nuclear magnetic resonance spectroscopy. Glucose production was determined with D-[6,6-(2)H(2)]glucose, and the hepatic uridine-diphosphate glucose pool was sampled with acetaminophen. Glycogen synthesis and breakdown as well as glucose production were identical in diabetic and healthy subjects: 7.3 +/- 0.9 vs. 7.1 +/- 0.7, 4.2 +/- 0.5 vs. 3.8 +/- 0.3, and 8.7 +/- 0.5 vs. 8.4 +/- 0.7 micromol x kg(-1) x min(-1), respectively. Although portal vein insulin concentrations were doubled, the flux through the indirect pathway of glycogen synthesis remained higher in type 1 diabetic subjects: approximately 70 vs. approximately 50%; P < 0.05. In conclusion, combined long- and short-term intensified insulin substitution normalizes rates of hepatic glycogen synthesis but not the contribution of gluconeogenesis to glycogen synthesis in type 1 diabetes.

Regulation by insulin of gene expression in human skeletal muscle and adipose tissue. Evidence for specific defects in type 2 diabetes

Defective regulation of gene expression may be involved in the pathogenesis of type 2 diabetes. We have characterized the concerted regulation by insulin (3-h hyperinsulinemic clamp) of the expression of 10 genes related to insulin action in skeletal muscle and in subcutaneous adipose tissue, and we have verified whether a defective regulation of some of them could be specifically encountered in tissues of type 2 diabetic patients. Basal mRNA levels (determined by reverse transcriptase-competitive polymerase chain reaction) of insulin receptor, insulin receptor substrate-1, p85alpha phosphatidylinositol 3-kinase (PI3K), p110alphaPI3K, p110betaPI3K, GLUT4, glycogen synthase, and sterol regulatory-element-binding protein-1c (SREBP-1c) were similar in muscle of control (n = 17), type 2 diabetic (n = 9), type 1 diabetic (n = 9), and nondiabetic obese (n = 9) subjects. In muscle, the expression of hexokinase II was decreased in type 2 diabetic patients (P < 0.01). In adipose tissue, SREBP-1c (P < 0.01) mRNA expression was reduced in obese (nondiabetic and type 2 diabetic) subjects and was negatively correlated with the BMI of the subjects (r = -0.63, P = 0.02). Insulin (+/-1,000 pmol/l) induced a two- to threefold increase (P < 0.05) in hexokinase II, p85alphaPI3K, and SREBP-1c mRNA levels in muscle and in adipose tissue in control subjects, in insulin-resistant nondiabetic obese patients, and in hyperglycemic type 1 diabetic subjects. Upregulation of these genes was completely blunted in type 2 diabetic patients. This study thus provides evidence for a specific defect in the regulation of a group of important genes in response to insulin in peripheral tissues of type 2 diabetic patients.

Effects of short-term improvement of insulin treatment and glycemia on hepatic glycogen metabolism in type 1 diabetes

Insufficiently treated type 1 diabetic patients exhibit inappropriate postprandial hyperglycemia and reduction in liver glycogen stores. To examine the effect of acute improvement of metabolic control on hepatic glycogen metabolism, lean young type 1 diabetic (HbA1c 8.8 +/- 0.3%) and matched nondiabetic subjects (HbA1c 5.4 +/- 0.1%) were studied during the course of a day with three isocaloric mixed meals. Hepatic glycogen concentrations were determined noninvasively using in vivo 13C nuclear magnetic resonance spectroscopy. Rates of net glycogen synthesis and breakdown were calculated from linear regression of the glycogen concentration time curves from 7:30-10:30 P.M. and from 10:30 P.M. to 8:00 A.M., respectively. The mean plasma glucose concentration was approximately 2.4-fold higher in diabetic than in nondiabetic subjects (13.6 +/- 0.4 vs. 5.8 +/- 0.1 mmol/l, P < 0.001). Rates of net glycogen synthesis and net glycogen breakdown were reduced by approximately 74% (0.11 +/- 0.02 vs. 0.43 +/- 0.04 mmol/l liver/min, P < 0.001) and by approximately 47% (0.10 +/- 0.01 vs. 0.19 +/- 0.01 mmol/l liver/min, P < 0.001) in diabetic patients, respectively. During short-term (24-h) intensified insulin treatment, the mean plasma glucose level was not different between diabetic and nondiabetic subjects (6.4 +/- 0.1 mmol/l). Net glycogen synthesis and breakdown increased by approximately 92% (0.23 +/- 0.04 mmol/l liver/min, P = 0.017) and by approximately 40% (0.14 approximately 0.01 mmol/l liver/min, P = 0.011), respectively. In conclusion, poorly controlled type 1 diabetic patients present with marked reduction in both hepatic glycogen synthesis and breakdown. Both defects in glycogen metabolism are improved but not normalized by short-term restoration of insulinemia and glycemia.

Severe insulin-resistant diabetes mellitus in patients with congenital muscle fiber type disproportion myopathy

Congenital muscle fiber type disproportion myopathy (CFTDM) is a chronic, nonprogressive muscle disorder characterized by universal muscle hypotrophy and growth retardation. Histomorphometric examination of muscle shows a preponderance of smaller than normal type 1 fibers and overall fiber size heterogeneity. Concomitant endocrine dysfunctions have not been described. We report the findings of altered insulin secretion and insulin action in two brothers affected with CFTDM and glucose intolerance as well as in their nonconsanguineous glucose-tolerant parents. Results are compared with those of six normoglycemic control subjects. All study participants underwent an oral glucose tolerance test to estimate insulin secretion. The oldest boy and his parents volunteered for studies of whole-body insulin sensitivity consisting of a 4-h euglycemic hyperinsulinemic clamp in combination with indirect calorimetry. Insulin receptor function and glycogen synthase (GS) activity and expression were examined in biopsies of vastus lateralis muscle. Despite a 45-90-fold increase in both fasting and postprandial serum insulin levels, both CFTDM patients had diabetes mellitus. Clamp studies revealed that the oldest boy had severe insulin resistance of both liver and peripheral tissues. The impaired insulin-stimulated glucose disposal to peripheral tissues was primarily due to reduced nonoxidative glucose metabolism. These changes were paralleled by reduced basal values of muscle GS total activity, allosterical activation of GS by glucose-6-phosphate, GS protein, and GS mRNA. The father expressed a lesser degree of insulin resistance, and studies of muscle insulin receptor function showed a severe impairment of receptor kinase activity. In conclusion, CFTDM is a novel form of severe hyperinsulinemia and insulin resistance. Whether insulin resistance is causally related to the muscle disorder awaits to be clarified.

The effects of non-insulin-dependent diabetes mellitus on the kinetics of onset of insulin action in hepatic and extrahepatic tissues

The mechanism(s) of insulin resistance in non-insulin-dependent diabetes mellitus remains ill defined. The current studies sought to determine whether non-insulin-dependent diabetes mellitus is associated with (a) a delay in the rate of onset of insulin action, (b) impaired hepatic and extrahepatic kinetic responses to insulin, and (c) an alteration in the contribution of gluconeogenesis to hepatic glucose release. To answer these questions, glucose disappearance, glucose release, and the rate of incorporation of 14CO2 into glucose were measured during 0.5 and 1.0 mU/kg-1 per min-1 insulin infusions while glucose was clamped at approximately 95 mg/dl in diabetic and nondiabetic subjects. The absolute rate of disappearance was lower (P < 0.05) and the rate of increase slower (P < 0.05) in diabetic than nondiabetic subjects during both insulin infusions. In contrast, the rate of suppression of glucose release in response to a change in insulin did not differ in the diabetic and nondiabetic subjects during either the low (slope 30-240 min:0.02 +/- 0.01 vs 0.02 +/- 0.01) or high (0.02 +/- 0.00 vs 0.02 +/- 0.00) insulin infusions. However, the hepatic response to insulin was not entirely normal in the diabetic subjects. Both glucose release and the proportion of systemic glucose being derived from 14CO2 (an index of gluconeogenesis) was inappropriately high for the prevailing insulin concentration in the diabetic subjects. Thus non-insulin-dependent diabetes mellitus slows the rate-limiting step in insulin action in muscle but not liver and alters the relative contribution of gluconeogenesis and glycogenolysis to hepatic glucose release.

Pre- and posttranslational upregulation of muscle-specific glycogen synthase in athletes

Expression of muscle-specific glycogen synthase (GS) and phosphofructokinase (PFK) was analyzed in seven athletes and eight control subjects who were characterized using the euglycemic, hyperinsulinemic (2 mU.kg-1.min-1) clamp technique in combination with indirect calorimetry and biopsy sampling of vastus lateralis muscle. In the basal state, total GS activity and half-maximal GS activation by glucose 6-phosphate (G-6-P) were respectively 34% (P < 0.03) and 50% (P < 0.005) higher in athletes than in control subjects. In parallel, GS mRNA/microgram total RNA in athletes was 40% (P < 0.005) higher. No difference in GS immunoreactive protein abundance was found between the groups. PFK activity and protein levels were respectively 15% (P < 0.05) and 20% (P < 0.02) lower in athletes, whereas no differences was found in the level of PFK mRNA. After 4 h of hyperinsulinemia, total glucose disposal rate (P < 0.005) and both nonoxidative (P < 0.02) and oxidative (P < 0.03) glucose metabolism were significantly higher in athletes. In parallel, after hyperinsulinemia, the relative activation of GS by G-6-P was significantly higher in athletes, whereas total activity and gene expression of both GS and PFK were unaffected by insulin. We conclude that athletes have increased whole body insulin-stimulated nonoxidative glucose metabolism associated with both pretranslational (mRNA) and posttranslational (enzyme activity) upregulation of GS. However, the immunoreactive mass of GS is normal, emphasizing that posttranslational regulation of the GS protein activity is important for the increased glycogen synthesis rate of muscle in endurance-trained individuals.

Glycogen synthase and phosphofructokinase protein and mRNA levels in skeletal muscle from insulin-resistant patients with non-insulin-dependent diabetes mellitus

In patients with non-insulin-dependent diabetes mellitus (NIDDM) and matched control subjects we examined the interrelationships between in vivo nonoxidative glucose metabolism and glucose oxidation and the muscle activities, as well as the immunoreactive protein and mRNA levels of the rate-limiting enzymes in glycogen synthesis and glycolysis, glycogen synthase (GS) and phosphofructokinase (PFK), respectively. Analysis of biopsies of quadriceps muscle from 19 NIDDM patients and 19 control subjects showed in the basal state a 30% decrease (P < 0.005) in total GS activity and a 38% decrease (P < 0.001) in GS mRNA/microgram DNA in NIDDM patients, whereas the GS protein level was normal. The enzymatic activity and protein and mRNA levels of PFK were all normal in diabetic patients. In subgroups of NIDDM patients and control subjects an insulin-glucose clamp in combination with indirect calorimetry was performed. The rate of insulin-stimulated nonoxidative glucose metabolism was decreased by 47% (P < 0.005) in NIDDM patients, whereas the glucose oxidation rate was normal. The PFK activity, protein level, and mRNA/microgram DNA remained unchanged. The relative activation of GS by glucose-6-phosphate was 33% lower (P < 0.02), whereas GS mRNA/micrograms DNA was 37% lower (P < 0.05) in the diabetic patients after 4 h of hyperinsulinemia. Total GS immunoreactive mass remained normal. In conclusion, qualitative but not quantitative posttranslational abnormalities of the GS protein in muscle determine the reduced insulin-stimulated nonoxidative glucose metabolism in NIDDM.

Hepatic and extrahepatic insulin action in humans: measurement in the absence of non-steady-state error

The isotope dilution technique has been extensively used to assess insulin action in humans. To determine if nonsteady state (NSS) has led to erroneous estimates of hepatic and extrahepatic insulin sensitivity, we measured glucose turnover in healthy subjects during infusion of insulin at rates of 0.25, 0.6, and 2.0 mU.kg-1.min-1. Turnover was calculated using Steele's traditional NSS equations [fixed-effective volume (pV) method] as well as with methods [radioactive infused glucose (hot-GINF) or variable pV] designed to minimize NSS error. In contrast to the fixed-pV method, both the hot-GINF and variable-pV methods indicated that several hours were required for suppression of hepatic glucose release at all insulin concentrations and that small increases in plasma insulin (approximately 100 pmol/l) had comparable effects on glucose disappearance and hepatic glucose release. Nevertheless, despite these differences, when turnover during the final hour of the insulin infusions was plotted vs. the prevailing insulin concentration, all three methods yielded similar insulin dose-response curves for suppression of hepatic glucose release. Thus despite previous errors in measurement of glucose turnover, the widely accepted belief that the human liver is exquisitely sensitive to small changes in insulin is correct.

Both acute and chronic near-normoglycaemia are required to improve insulin resistance in type 1 (insulin-dependent) diabetes mellitus

To determine the impact of both short- and long-term "near-normoglycaemia" on insulin resistance in Type 1 (insulin-dependent) diabetes hepatic glucose production (mg.kg-1.min-1) and peripheral glucose utilisation ("M-value", mg.kg-1.min-1) were estimated during an euglycaemic hyperinsulinaemic clamp (10 mU.kg.min) in patients with either good (HbA1c < 5.8%, groups A and B) or poor (HbA1c > 7.5%, groups C and D) long-term metabolic control (time > 12 months) and in healthy subjects (HbA1c: 5.08 +/- 0.20%; n = 8). To this end blood glucose was stabilized at 6.7 mmol/l by overnight (t = 12 h) i.v. regular insulin in groups (n = 8 each) A (HbA1c: 5.49 +/- 0.46%) and C (HbA1c: 8.83 +/- 1.20%), while groups B (HbA1c: 5.55 +/- 0.19%) and D (HbA1c: 8.51 +/- 1.09%) were kept overnight on long-acting insulin without feed-back control of blood glucose before euglycaemic clamping. Thereby, pre-equilibration of blood glucose at 6.7 mmol/l was shown to normalize basal hepatic glucose production (A: 2.27 +/- 0.48; C 2.50 +/- 0.57 mg.kg-1.min-1) despite different HbA1c values, whereas basal hepatic glucose production stayed elevated in groups B (3.09 +/- 0.38 mg.kg-1.min-1) and D (3.21 +/- 0.58 mg.kg-1.min-1) with poor actual glycaemia (B: 10.9 +/- 4.6; D: 12.1 +/- 4.6 mmol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of hyperglycemia per se on glucose turnover rates in patients with insulin-dependent diabetes

The effect of hyperglycemia, per se, on glucose utilization and hepatic glucose production was reevaluated in eight C-peptide-negative insulin-dependent diabetic patients using primed-continuous noncontaminated 3-3H-glucose infusion and labeled glucose infusates. The night before study, euglycemia was maintained by a variable insulin infusion. During the studies, insulin was infused at basal replacement rates determined as the rate required to maintain euglycemia in the morning. After a 2-hour equilibration period, either plasma glucose level was increased to 12 mmol/L for 4 hours using a variable glucose infusion, or no glucose was infused (control day). On the hyperglycemic day, glucose utilization increased 16% (86 +/- 2 to 99 +/- 4 mg.m-2.min-1, P < .02) and glucose production decreased 45% (85 +/- 3 to 47 +/- 4 mg.m-2.min-1, P < .01). On the control day, both glucose utilization and glucose production decreased (84 +/- 3 to 68 +/- 3 and 84 +/- 3 to 65 +/- 3 mg.m-2.min-1, respectively; both P < .01). Therefore, comparing rates at the end of the hyperglycemic and control studies, glucose utilization was increased by 45% and glucose production was decreased by 28% in response to hyperglycemia (both P < .01). Thus hyperglycemia, at basal insulin levels enhanced glucose utilization and suppressed glucose production in insulin-dependent diabetic patients. Quantitatively, the enhancement of glucose utilization was more important than the suppressive effect on glucose production.

Decreased hepatic glucagon responses in type 1 (insulin-dependent) diabetes mellitus

The effect of glucagon infusion on hepatic glucose production during euglycaemia was evaluated in seven Type 1 (insulin-dependent) diabetic patients and in ten control subjects. In the diabetic subjects normoglycaemia was maintained during the night preceding the study by a variable intravenous insulin and glucose infusion. During the study endogenous insulin secretion was suppressed by somatostatin (450 micrograms/h) and replaced by insulin infusion (0.15 mU.kg-1.min-1). 3H-glucose was infused for isotopic determination of glucose turnover. Plasma glucose was clamped at 5 mmol/l for 2 h 30 min and glucagon (1.5 ng.kg-1.min-1) was then infused for the following 3 h. Hepatic glucose production and glucose utilisation were measured during the first, second and third hour of the glucagon infusion. Basal hepatic glucose production (just prior to glucagon infusion) was similar in diabetic (1.2 +/- 0.3 mg.kg-1.min-1) and control (1.6 +/- 0.1 mg.kg-1.min-1) subjects. In diabetic patients hepatic glucose production rose slowly to 2.1 +/- 0.5 mg.kg-1.min-1 during the first hours of glucagon infusion and stabilized at this level (2.4 +/- 0.5 mg.kg-1.min-1) in the third hour. In control subjects hepatic glucose production increased sharply to higher levels than in the diabetic subjects (3.4 +/- 0.3 mg.kg-1.min-1) during the first and second hour of glucagon infusion (p less than 0.05) and then gradually fell (2.9 +/- 0.4 mg.kg-1.min-1) during the third hour. In conclusion, when stimulated with glucagon at a physiologic plasma concentration diabetic patients had 1) an overall reduced hepatic glucose production response and 2) an abnormal sluggish response pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced glycogen synthase activity in skeletal muscle from obese patients with and without type 2 (non-insulin-dependent) diabetes mellitus

In order to evaluate the importance of a defect in insulin mediated non-oxidative glucose metabolism and glycogen synthase activity in skeletal muscles in obese subjects with and without Type 2 (non-insulin-dependent) diabetes mellitus we studied: 10 lean and 10 obese control subjects and 12 obese diabetic patients using the euglycaemic hyperinsulinaemic clamp technique (basal, 20 mU.(m2)-1.min-1, 80 mU.(m2)-1.min-1) in combination with indirect calorimetry. Muscle biopsies were taken from m. vastus lateralis at each insulin level. We found that non-oxidative glucose metabolism could be stimulated by insulin in all three groups (p less than 0.01). The values obtained at the highest insulin levels (around 140 microU/ml) were lower in both obese groups compared to the lean control subjects (118 +/- 21, 185 +/- 31, 249 +/- 14 mg.(m2)-1.min-1 (p less than 0.01]. Insulin stimulation of the glycogen synthase activity at a glucose-6-phosphate concentration of 0.1 mmol/l was absent in both obese groups, while activities increased significantly in the lean control subjects (19.6 +/- 4.2% to 45.6 +/- 6.8%, p less than 0.01). Glycogen synthase activities at the highest insulin concentrations only differed significantly between lean control subjects and obese diabetic patients (45 +/- 7% and 31 +/- 5%, p less than 0.05). We conclude that insulin resistance in peripheral tissues in obese subjects with and without Type 2 diabetes may be partly explained by a reduced insulin mediated non-oxidative glucose metabolism and that this abnormality might be due to an absent insulin stimulation of glycogen synthase in skeletal muscles. This enzyme defect is correlated to obesity itself.

Effects of a growth hormone pulse on total and forearm substrate fluxes in humans

Under physiological circumstances growth hormone (GH) is secreted in bursts after the onset of sleep and a few hours postprandially. Because most relevant studies have employed constant or repeated infusion of high doses of GH, the possible metabolic effects of such bursts are largely unknown. We have studied seven healthy, male subjects for 7 h after an intravenous bolus of 1) 140 micrograms GH and 2) saline. When injected, serum GH rose to a peak of 21 +/- 3 micrograms/l 10 min after injection. GH caused 1) a rapid, sustained 55% decrease in forearm glucose uptake (P less than 0.05) followed by increases toward control values, 2) a delayed 5 mg/100 ml decrease in plasma glucose (P less than 0.05), and 3) significant 60-250% increases (P less than 0.05) in all measured lipid intermediates (nonesterified fatty acids, 3-hydroxybutyrate, and glycerol) 120-160 min after administration followed by decreases to below control values (P less than 0.05). GH did not influence circulating levels of insulin, C-peptide, glucagon, or insulin-like growth factor I (IGF-I), or isotopically determined glucose turnover. Physiological bursts of GH secretion appear to have acute insulin antagonistic effects with maximal effect on lipolysis after 2 h. These effects are reversed after 4 h. Therefore, GH could play a key role in regulation of diurnal rhythms of substrate levels and fuel utilization in humans.

The course and determinants of insulin action in type 1 (insulin-dependent) diabetes mellitus

The course and determinants of insulin action were investigated in 8 newly diagnosed Type 1 (insulin-dependent) diabetic patients, who were studied every 3 months for one year, and in three groups of 8 patients each with 5, 10 and 20 years diabetes, studied once. Fifteen healthy subjects matched for age, sex and body weight served as control subjects. Dose-response curves were constructed using sequential euglycaemic (5.0 mmol/l) clamps (insulin infusion rates: 0.5, 1.0, 2.0 and 5.0 mU.kg-1.min-1 in periods of 2h). After 1/2 month of insulin treatment, insulin responsiveness was normal, but sensitivity was decreased (ED50 70 +/- 7 mU/l (SEM) vs 54 +/- 4 mU/l in control subjects, p less than 0.05). After 6 months, insulin sensitivity was improved (ED50 57 +/- 4 mU/l, p less than 0.01 vs 1/2 month and not significant (NS) vs control subjects); but after 9 and 12 months, it was reduced again, similarly to 0.5 month. Insulin responsiveness remained normal at all time-points. In the three groups of patients with longstanding diabetes, impaired insulin sensitivity with normal responsiveness was noted also (ED50 73 +/- 9 mU/l, p less than 0.02 vs control subjects). At 6, 9 and 12 months, glycaemic control (HbA1) and insulin dose were inverse correlates for insulin action; in patients with longstanding disease, this was noted for HbA1 and body weight, in control subjects for body weight. In conclusion, decreased insulin sensitivity re-develops in Type 1 diabetes within the first year following an initial improvement.(ABSTRACT TRUNCATED AT 250 WORDS)