Increased plasma amylin in type 1 diabetic patients after kidney and pancreas transplantation: A sign of impaired beta-cell function?

OBJECTIVE: In response to hyperglycemia, beta-cells release insulin and C-peptide, as well as islet amyloid pancreatic polypeptide, which is involved in glucose homeostasis. After successful pancreas-kidney transplantation (PKT), type 1 diabetic patients may revert to a nondiabetic metabolism without exogenous insulin therapy and re-secrete all beta-cell hormones. RESEARCH DESIGN AND METHODS: Using mathematical models, we investigated hormone (amylin, insulin, C-peptide) and metabolite (glucose, free fatty acids) kinetics, beta-cell sensitivity to glucose, and oral glucose insulin sensitivity index (OGIS) in 11 nondiabetic type 1 diabetic patients after PKT (BMI 25 +/- 1 kg/m2, 47 +/- 2 years of age, 4 women/7 men, glucocorticoid-free), 6 matching nondiabetic patients after kidney transplantation (25 +/- 1 kg/m2, 50 +/- 5 years, 3 women/3 men, on glucocorticoids), and 9 matching nondiabetic control subjects (24 +/- 1 kg/m2, 47 +/- 2 years, 4 women/5 men) during a 3-h 75-g oral glucose tolerance test (OGTT). RESULTS: PKT patients had higher fasting amylin (19 +/- 3 vs. control subjects: 7 +/- 1 pmol/l) and insulin (20 +/- 2 vs. control subjects: 10 +/- 1 microU/ml; each P < 0.01) levels. Kidney transplant subjects showed increased OGTT plasma insulin at 90 min and C-peptide levels (each P < 0.05). In PKT patients, plasma glucose from 90 to 150 min was 9-31% higher (P < 0.05 vs. control subjects). Amylin clearance was comparable in all groups. Amylin's plasma concentrations and area under the concentration curve were up to twofold higher in PKT patients during OGTT (P < 0.05). OGIS was not significantly different between groups. beta-Cell sensitivity to glucose was reduced in PKT patients (-64%, P < 0.009). Fasting plasma amylin was inversely associated with beta-cell sensitivity to glucose (r = -0.543, P < 0.004). CONCLUSIONS: After successful PKT, type 1 diabetic patients with nondiabetic glycemia exhibit increased fasting and post-glucose load plasma amylin, which appears to be linked to impaired beta-cell function. Thus, higher amylin release in proportion to insulin might also reflect impaired beta-cell function in type 1 diabetic patients after PKT.     

Intact proinsulin and beta-cell function in lean and obese subjects with and without type 2 diabetes

OBJECTIVE: Type 2 diabetes is a heterogeneous disease in which both beta-cell dysfunction and insulin resistance are pathogenetic factors. Disproportionate hyperproinsulinemia (elevated proinsulin/insulin) is another abnormality in type 2 diabetes whose mechanism is unknown. Increased demand due to obesity and/or insulin resistance may result in secretion of immature beta-cell granules with a higher content of intact proinsulin. RESEARCH DESIGN AND METHODS: We investigated the impact of obesity on beta-cell secretion in normal subjects and in type 2 diabetic patients by measuring intact proinsulin, total proinsulin immunoreactivity (PIM), intact insulin, and C-peptide (by radioimmunoassay) by specific enzyme-linked immunosorbent assays in the fasting state and during a 120-min glucagon (1 mg i.v.) stimulation test. Lean (BMI 23.5 +/- 0.3 kg/m2) (LD) and obese (30.1 +/- 0.4 kg/m2) (OD) type 2 diabetic patients matched for fasting glucose (10.2 +/- 0.6 vs. 10.3 +/- 0.4 mmol/l) were compared with age- and BMI-matched lean (22.4 +/- 0.6 kg/m2) (LC) and obese (30.8 +/- 0.9 kg/m2) (OC) normal control subjects. RESULTS: Diabetic patients (LD vs. LC and OD vs. OC) had elevated fasting levels of intact proinsulin 6.6 +/- 1.0 vs. 1.6 +/- 0.3 pmol/l and 7.7 +/- 2.0 vs. 1.2 +/- 0.2 pmol/l; PIM: 19.9 +/- 2.5 vs. 5.4 +/- 1.0 pmol/l and 29.6 +/- 6.1 vs. 6.1 +/- 0.9 pmol/l; and total PIM/intact insulin: 39 +/- 4 vs. 15 +/- 2% and 35 +/- 5 vs. 13 +/- 2%, all P < 0.01. After glucagon stimulation, PIM levels were disproportionately elevated (PIM/intact insulin based on area under the curve analysis) in diabetic patients (LD vs. LC and OD vs. OC): 32.6 +/- 6.7 vs. 9.2 +/- 1.1% and 22.7 +/- 5.2 vs. 9.1 +/- 1.1%, both P < 0.05. Intact insulin and C-peptide net responses were significantly reduced in type 2 diabetic patients, most pronounced in the lean group. The ratio of intact proinsulin to PIM was higher in diabetic patients after stimulation in both LD versus LC: 32 +/- 3 vs. 23 +/- 2%, and OD versus OC: 28 +/- 4 vs. 16 +/- 2%, both P < 0.01. In obese normal subjects, intact proinsulin/PIM was lower both in the fasting state and after glucagon stimulation: OC versus LC: 22 +/- 3 vs. 33 +/- 3% (fasting) and 16 +/- 2 vs. 23 +/- 2% (stimulated), both P < 0.05. CONCLUSIONS: Increased secretory demand from obesity-associated insulin resistance cannot explain elevated intact proinsulin and disproportionate hyperproinsulinemia in type 2 diabetes. This abnormality may be an integrated part of pancreatic beta-cell dysfunction in this disease.     

Impaired insulin sensitivity, insulin secretion, and glucose effectiveness predict future development of impaired glucose tolerance and type 2 diabetes in pre-diabetic African Americans: implications for primary diabetes prevention

OBJECTIVE: We examined the determinants of impaired glucose tolerance (IGT) and type 2 diabetes in first-degree relatives of African-American type 2 diabetic patients over 5-8 years (median 6). RESEARCH DESIGN AND METHODS: A total of 81 healthy subjects (age 41.5 +/- 4.8 years; BMI 31.3 +/- 3.6 kg/m(2)) participated in the study. Each subject underwent an oral glucose tolerance test (OGTT) and a frequently sampled intravenous glucose tolerance test at baseline. Insulin sensitivity index (S(i)) and glucose effectiveness index (S(g)) were determined by the minimal model method. Homeostasis model assessment (HOMA) was used to estimate insulin resistance (HOMA-IR) and beta-cell function (HOMA-%B). A total of 18 subjects progressed to either IGT or type 2 diabetes (progressors), whereas 19 subjects maintained normal glucose tolerance (nonprogressors). RESULTS: Comparing the progressors and nonprogressors, mean fasting serum glucose levels (95 +/- 8 vs. 80 +/- 14 mg/dl, P < 0.01) and 2-h serum glucose levels (149 +/- 27 vs. 100 +/- 60 mg/dl, P < 0.01) as well as 2-h serum insulin levels (117 +/- 81 vs. 72 +/- 87 microU/ml, P < 0.01) during OGTT were higher at baseline. Mean acute first-phase insulin secretion (205 +/- 217 vs. 305 +/- 230 microU/ml), HOMA-%B (148 +/- 60 vs. 346 +/- 372, P < 01), S(i) (1.61 +/- 1.13 vs. 2.48 +/- 1.25 x 10(-4). min(-1) [microU/ml](-1)), and S(g) (1.48 +/- 0.61 vs. 2.30 +/- 0.97 x 10(-2). min(-1)) were lower in the progressors than in the nonprogressors at baseline. Mean HOMA-IR (3.31 +/- 1.64 vs. 2.36 +/- 1.64) was significantly greater in the progressors than the nonprogressors. At the time of diagnosis of glucose intolerance (IGT + diabetes), HOMA-%B (101 +/- 48 vs. 148 +/- 60, P < 0.001) and HOMA-IR (5.44 +/- 2.55 vs. 3.31 +/- 1.64, P < 0.003) deteriorated in the progressors versus baseline. CONCLUSIONS: We conclude that nondiabetic, first-degree relatives of African-American type 2 diabetic patients who progressed to IGT and type 2 diabetes manifest triple defects (decreased insulin secretion, insulin action, and glucose effectiveness) that antecede the disease.     

Fenfluramine increases insulin action in patients with NIDDM

These studies examined the effect of fenfluramine on insulin action and insulin secretion in healthy subjects and patients with non-insulin-dependent diabetes mellitus (NIDDM). In the first study, a double-blind crossover design was used in healthy subjects to compare the effect of short-term fenfluramine therapy (60 mg orally for 3 days) with placebo. Insulin secretion and whole-body insulin sensitivity (determined by frequently sampled intravenous glucose tolerance tests with analysis by the minimal-model method) were unchanged by fenfluramine. In the second study, involving patients with NIDDM inadequately controlled on submaximal to maximal doses of oral hypoglycemic agents, a double-blind crossover strategy was used to compare baseline studies (conducted after a run-in period) with fenfluramine (60 mg orally) or placebo for 4 wk. There was a significant fall in fasting blood glucose after therapy with fenfluramine compared with the baseline study period (13.0 +/- 1.2 vs. 8.4 +/- 0.89 mM, mean +/- SE, P less than .01) with no significant fall in fasting serum insulin (20 +/- 2 vs. 24 +/- 3 microU/ml) or C-peptide (1.3 +/- 0.2 vs. 1.3 +/- 0.1 nM). During euglycemic-hyperinsulinemic (1 mU.kg-1.min-1) clamp studies there was a significant increase in insulin action from 12.7 +/- 2.3 to 17.3 +/- 1.8 min-1.10(3) microU.ml-1 (P less than .05), although clamp insulin levels were lower after fenfluramine treatment (136 +/- 14 vs. 96 +/- 9 microU/ml, P less than .02), reflecting an enhanced metabolic clearance rate for insulin (12.7 +/- 1.5 vs. 20.1 +/- 2.1 ml.kg-1.min-1, P less than .025).(ABSTRACT TRUNCATED AT 250 WORDS)     

Significance of spontaneous ketonuria and serum C-peptide levels in obese type II diabetic patients

Patients with type II diabetes mellitus (type II DM patients) are characteristically obese, hyperinsulinemic, and non-ketosis prone. Recently, we have encountered several obese type II DM patients with either diabetic ketoacidosis or significant ketonuria after insulin withdrawal. There was no evidence of infection, stress, or starvation to explain their ketonuria. Therefore, we assessed serum connecting peptide (C-peptide) response to oral glucose in 14 obese, insulin-treated type II DM patients: 6 with and 8 without episodes of spontaneous ketonuria. The group presenting with ketonuria had low to absent basal and stimulated serum C-peptide responses. The nonketonuric group had higher basal C-peptide (P less than 0.01) concentrations that increased significantly (P less than 0.001) after oral glucose compared with those of the ketonuric group. Clinical characteristics and biochemical control were similar in both groups. Our findings confirm that obese type II diabetes mellitus is a heterogeneous disease with variable fasting and stimulated C-peptide responses. Spontaneous ketonuria could be a feature in the clinical presentation of the patients especially in the presence of both low fasting and stimulated C-peptide levels. The significance of these findings is unclear but suggests individualization in the management of type II DM patients and cautious withdrawal of insulin therapy in such patients. Furthermore, serum C-peptide levels alone cannot be recommended to classify patients into either type I or type II diabetes mellitus.     

Decreased serum C-peptide/insulin molar ratios after oral glucose ingestion in hyperthyroid patients

Since C-peptide/immunoreactive insulin (IRI) molar ratios may reflect hepatic extraction of insulin, we measured simultaneous serum glucose, IRI, and C-peptide levels during fasting and 30, 60, 90, 120, and 180 min after 75 g of oral glucose in 10 hyperthyroid patients and 10 age- and weight-matched controls. Mean fasting serum glucose and IRI levels were significantly higher in the hyperthyroid versus control subjects (glucose: 4.9 +/- 0.3 mmol/L versus 4.36 +/- 0.11 mmol/L, P less than 0.01; IRI: 0.10 +/- 0.02 pmol/ml versus 0.05 +/- 0.01 pmol/ml; P less than 0.025). After glucose, mean serum glucose levels were significantly higher in the hyperthyroid versus control subjects at all times studied except for 180 min (P less than 0.01). Mean IRI levels were significantly higher at all times studied including 180 min (P less than 0.01). Mean fasting C-peptide levels were significantly greater in the hyperthyroid patients compared with the controls (1.2 +/- 0.25 pmol/ml versus 0.62 +/- 0.09 pmol/ml; P less than 0.025). After oral glucose, mean C-peptide levels were significantly higher (P less than 0.025) in the hyperthyroid compared with control subjects at 30-60 min but not at 90-180 min. Molar ratios of C-peptide/IRI were significantly lower (P less than 0.05) in the hyperthyroid versus control subjects at all times studied except fasting. In summary, glucose intolerance and hyperinsulinism occur in hyperthyroidism. In addition, C-peptide/IRI molar ratios are reduced after oral glucose ingestion.     

Diminished insulin secretory response to glucose but normal insulin and glucagon secretory responses to arginine in a family with maternally inherited diabetes and deafness caused by mitochondrial tRNA(LEU(UUR)) gene mutation.

OBJECTIVE: The effects of glucose, arginine, and glucagon on beta-cell function as well as alpha-cell response to arginine were studied in a family with mitochondrial diabetes. RESEARCH DESIGN AND METHODS: The function of alpha- and beta-cells was assessed in all five siblings carrying the mitochondrial tRNA Leu(UUR) gene mutation at position 3243 and compared with six sex-, age-, and weight-matched control subjects. Insulin and C-peptide responses were evaluated by intravenous glucagon application, intravenous arginine stimulation test, and intravenous glucose tolerance test. Glucagon secretion was assessed during the arginine stimulation test. RESULTS: The glucose disappearance constant (K(g)) value (mean +/- SEM 0.61 +/- 0.04 vs. 1.1 +/- 0.04, P = 0.0002) as well as the acute insulin response to glucose (area under the curve [AUC] 0-10 min, 77.7 +/- 50.7 vs. 1,352.3 +/- 191.5 pmol/l, P = 0.0004) were decreased in all patients. Similarly, glucagon-stimulated C-peptide response was also impaired (728 +/- 111.4 vs. 1,526.7 +/- 157.7 pmol/l, P = 0.005), whereas the insulin response to arginine (AUC) was normal (1,346.9 +/- 710.8 vs. 1,083.2 +/- 132.5 pmol/l, P = 0.699). Acute glucagon response to arginine (AUC) was normal but tended to be higher in the patients than in the control subjects (181.7 +/- 47.5 vs. 90.0 +/- 21.1 pmol/l, P = 0.099). CONCLUSIONS: This study shows impaired insulin and C-peptide secretion in response to a glucose challenge and to glucagon stimulation in diabetic patients with mitochondrial tRNA Leu(UUR) gene mutation, although insulin and glucagon secretory responses to arginine were normal.     

Twenty-four hour C-peptide and insulin secretion rates and diurnal profiles of glucose, lipids and intermediary metabolites in cirrhosis.

1. To examine the contributions of hypersecretion and decreased insulin clearance to the hyperinsulinaemia of cirrhosis, insulin secretion was calculated over the day from serum C-peptide concentrations and C-peptide metabolic clearance rate. The latter was measured during infusions of recombinant human C-peptide. In cirrhotic patients (n = 9) insulin secretion rate was twice that of normal control subjects (n = 10), both in the basal state [02.00-07.00 hours, 15.7 +/- 2.1 (mean +/- SEM) nmol/h (2.6 +/- 0.4 units/h) versus 7.0 +/- 0.9 nmol/h (1.2 +/- 0.2 units/h), P < 0.002] and over 24 h [787 +/- 93 nmol (132 +/- 16 units) versus 346 +/- 34 nmol (58 +/- 6 units), P < 0.001]. However, the area under the serum insulin concentration curve was approximately six times greater in the cirrhotic patients (24 h basal, 6.3 +/- 1.0 versus 1.1 +/- 0.3 nmol l-1 h, P < 0.001; 24 h total, 21.7 +/- 3.2 versus 3.7 +/- 0.7 nmol l-1 h, P < 0.001). Thus, despite impairment of insulin clearance there is continuing hypersecretion of insulin in cirrhosis. 2. The relationship of carbohydrate and lipid metabolism with insulin secretion was assessed. In cirrhotic patients, 24 h blood glucose profiles showed a worsening of glucose tolerance over breakfast, despite greater insulin secretion compared with other meals, suggesting that the insulin insensitivity of cirrhosis is worse at this time. 3. Cirrhotic patients showed impaired suppression of blood glycerol levels after meals but normal suppression of serum non-esterified fatty acid concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Decreased insulin response to glucose in islet cell antibody-negative siblings of type 1 diabetic children.

Measurement of beta-cell function is an important marker of progression to diabetes in individuals at risk for the disease. Although the peak incidence for the disease occurs before 17 years of age, normal values for insulin secretion were not available in this age group. We performed a simplified intravenous glucose tolerance test in 167 normal children, and in 98 islet cell antibody (ICA)-negative and 12 ICA-positive siblings of diabetic patients. Their age range was 1-16 yr. The first phase of insulin secretion, evaluated as the sum of plasma insulin concentrations at 1 and 3 min, increased with age and was significantly lower in ICA-negative siblings (86 +/- 6 microU/ml, P < 0.002) than in normal controls (115 +/- 6 microU/ml). This difference was not apparent before 8 yr of age. None of the ICA-negative siblings developed diabetes after an average of 4.5 yr. ICA-positive siblings at first study had a first phase insulin response similar to that of ICA negative siblings, but significantly lower than that of the normal controls (74 +/- 13 microU/ml, P < 0.02). The reason for the decreased insulin secretion in ICA-negative siblings is unknown, but could involve a defect in the growth of beta-cell mass or insulin secretion that could be part of the multifactorial pathogenesis of type 1 diabetes.     

Urinary C-peptide measurements in patients receiving continuous and cyclic total parenteral nutrition

Urinary C-peptide excretion has been found to be an accurate index of insulin secretion under a variety of physiologic conditions, such as acute starvation and exercise, and after oral and intravenous glucose administration. We investigated urinary C-peptide responses in a group of patients who were receiving all of their nutrient intake by intravenous administration. In these patients receiving total parenteral nutrition (TPN), we were able to monitor changes in insulin secretion when the same nutrients were infused at different rates, for example, during cyclic vs. continuous TPN administration, and to observe changes in the insulin secretory response as the pattern of nutrient delivery was altered in the same individual. We found that increasing the TPN infusion rate by 50% during cyclic TPN caused a 65% increase in serum insulin levels over levels observed during continuous TPN administration (93 vs. 60 microU/ml), whereas a 100% increase in the cyclic TPN infusion rate above the continuous TPN rate increased insulin levels by 147% (147 vs. 60 microU/ml). The molar ratio of insulin to C-peptide was increased by increasing rates of TPN infusion, from 0.116 during fasting periods to 0.151 during maximum rates of TPN administration. An additional finding of this study is that 24-hour insulin secretion, estimated by urinary C-peptide measurements, was equivalent in all treatments regardless of the pattern of insulin response elicited.     

Human insulin production and amelioration of diabetes in mice by electrotransfer-enhanced plasmid DNA gene transfer to the skeletal muscle

A first-line gene therapy for type 1 diabetes should be based on a safe procedure to engineer an accessible tissue for insulin release. We evaluated the ability of the skeletal muscle to release human insulin after electrotransfer (ET)-enhanced plasmid DNA injection in mice. A furin-cleavable proinsulin cDNA under the CMV or the MFG promoter was electrotransferred to immune-incompetent mice with STZ-induced severe diabetes. At 1 week, mature human insulin was detected in the serum of 17/20 mice. After an initial peak of 68.5 +/- 34.9 microU/ml, insulin was consistently detected at significant levels up to 6 weeks after gene transfer. Importantly, untreated diabetic animals died within 3 weeks after STZ, whereas treated mice survived up to 10 weeks. Fed blood glucose (BG) was reduced in correspondence with the insulin peak. Fasting BG was near-normalized when insulin levels were 12.9 +/- 5.3 (CMV group, 2 weeks) and 7.7 +/- 2.6 microU/ml (MFG group, 4 weeks), without frank hypoglycemia. These data indicate that ET-enhanced DNA injection in muscle leads to the release of biologically active insulin, with restoration of basal insulin levels, and lowering of fasting BG with increased survival in severe diabetes. Therefore the skeletal muscle can be considered as a platform for basal insulin secretion.     

Effects of 8-wk alpha-glucosidase inhibition on metabolic control, C-peptide secretion, hepatic glucose output, and peripheral insulin sensitivity in poorly controlled type II diabetic patients

Miglitol (BAYm 1099), an alpha-glucosidase inhibitor, reduces the postprandial increase of blood glucose and serum insulin levels in type II (non-insulin-dependent) diabetes mellitus, as shown in short-term studies. In this study, the effects of long-term miglitol treatment on metabolic control, C-peptide secretion, hepatic glucose output, and peripheral insulin sensitivity (euglycemic clamp) were tested in 15 type II diabetic patients (8 receiving insulin, 7 receiving oral hypoglycemic agents). For 8 wk they received either miglitol (300 mg/day) or placebo with a double-blind crossover design that had a 4-wk washout period between treatments. Miglitol therapy induced a reduction of postprandial blood glucose levels (miglitol compared with placebo; areas under the curve; P less than .002), whereas fasting blood glucose levels were not influenced. Miglitol caused a slight reduction of glycosylated hemoglobin levels (mean +/- SE miglitol and placebo 9.50 +/- 0.3 and 10.0 +/- 0.4%, respectively; P less than .05), which was more pronounced in insulin-treated patients. Miglitol caused a reduction of postprandial C-peptide increase (P less than .03). Hepatic glucose output (both in the basal state and during euglycemic clamp conditions) and peripheral insulin sensitivity were not influenced by miglitol therapy. Specific side effects were observed in 11 patients; in 6 patients only to a moderate degree. Long-term miglitol treatment induces a persistent reduction of postprandial blood glucose increase. This effect is more pronounced in type II diabetic patients on insulin therapy, which can cause a moderate improvement of overall metabolic control.     

Defective suppression by insulin of leucine-carbon appearance and oxidation in type 1, insulin-dependent diabetes mellitus. Evidence for insulin resistance involving glucose and amino acid metabolism.

To determine whether a resistance to insulin in type 1, insulin-dependent diabetes mellitus (IDDM) is extended to both glucose and amino acid metabolism, six normal subjects and five patients with IDDM, maintained in euglycemia with intravenous insulin administration, were infused with L-[4,5-3H]leucine (Leu) and [1-14C]alpha ketoisocaproate (KIC). Steady-state rates of leucine-carbon appearance derived from protein breakdown (Leu + KIC Ra) and KIC (approximately leucine) oxidation were determined at basal and during sequential euglycemic, hyperinsulinemic (approximately 40, approximately 90 and approximately 1,300 microU/ml) clamps. In the euglycemic postabsorptive diabetic patients, despite basal hyperinsulinemia (24 +/- 6 microU/ml vs. 9 +/- 1 microU/ml in normals, P less than 0.05), Leu + KIC Ra (2.90 +/- 0.18 mumol/kg X min), and KIC oxidation (0.22 +/- 0.03 mumol/kg X min) were similar to normal values (Leu + KIC Ra = 2.74 +/- 0.25 mumol/kg X min) (oxidation = 0.20 +/- 0.02 mumol/kg X min). During stepwise hyperinsulinemia, Leu + KIC Ra in normals decreased to 2.08 +/- 0.19, to 2.00 +/- 0.17, and to 1.81 +/- 0.16 mumol/kg X min, but only to 2.77 +/- 0.16, to 2.63 +/- 0.16, and to 2.39 +/- 0.08 mumol/kg X min in the diabetic patients (P less than 0.05 or less vs. normals at each clamp step). KIC oxidation decreased in normal subjects to a larger extent than in the diabetic subjects. Glucose disposal was reduced at all insulin levels in the patients. In summary, in IDDM: (a) Peripheral hyperinsulinemia is required to normalize both fasting leucine metabolism and blood glucose concentrations. (b) At euglycemic hyperinsulinemic clamps, lower glucose disposal rates and a defective suppression of leucine-carbon appearance and oxidation were observed. We conclude that in type 1 diabetes a resistance to the metabolic effects of insulin on both glucose and amino acid metabolism is present.     

An in vivo and in vitro study of the mechanism of prednisone-induced insulin resistance in healthy subjects.

Prednisone-induced insulin resistance may depend on either reduced sensitivity (receptor defect) or reduced response to insulin (postreceptor defect). To clarify the mechanism of prednisone-induced insulin resistance, a [3H]glucose infusion (1 microCi/min) was performed for 120 min before and during a euglycemic clamp repeated at approximately 100, approximately 1,000, and approximately 10,000 microU/ml steady state plasma insulin concentration in 10 healthy, normal weight subjects, aged 35 +/- 7 yr. Each test was repeated after 7-d administration of placebo or prednisone (15 plus 15 mg/d per subject), in a randomized sequence with an interval of 1 mo between the two tests. Mean fasting blood glucose (89.5 +/- 2.1 vs. 83.7 +/- 1.9 mg/dl) and mean fasting plasma insulin values (17.8 +/- 1.2 vs. 14.3 +/- 0.8 microU/ml) were significantly higher (P less than 0.01) after prednisone. The insulin sensitivity index (glucose metabolic clearance rate in ml/kg per min) was significantly lower (P less than 0.001) after prednisone at all three steady state plasma insulin levels: 2.8 +/- 0.3 vs. 7.4 +/- 1.1 at approximately 100 microU/ml; 6.0 +/- 0.5 vs. 12.2 +/- 1.1 at approximately 1,000 microU/ml; 7.4 +/- 0.6 vs. 14.4 +/- 0.5 at approximately 10,000 microU/ml. Fasting glucose production (in mg/kg per min) was significantly higher after prednisone: 3.7 +/- 0.2 vs. 2.9 +/- 0.2, P less than 0.001. Suppression of glucose production at steady state plasma insulin level of approximately 100 microU/ml was less after prednisone (1.01 +/- 0.35 vs. 0.14 +/- 0.13, NS), and total at approximately 1,000 and approximately 10,000 microU/ml after both prednisone and placebo. The metabolic kinetic parameters of insulin after prednisone were not significantly different from those after placebo. In addition, insulin binding and 3-ortho-methyl-glucose transport were studied in vitro on fat cells from 16 normal-weight surgical candidates aged 40 +/- 8 yr (10 treated with placebo and 6 with prednisone as above). No significant difference was observed with regard to specific insulin binding (tested with 1 ng/ml hormone only), whereas significant transport differences were noted at the basal level (0.40 +/- 0.10 vs. 0.54 +/- 0.12 pmol/10(5) cells, P less than 0.05), and at increasing concentrations up to the maximum stimulation values (5 ng/ml): 0.59 +/- 0.04 vs. 0.92 +/- 0.12 pmol/10(5) cells, P less than 0.005. These results suggest that (a) administration of an anti-inflammatory dose of prednisone for 7 d induces insulin resistance in man; (b) this is more dependent on depressed peripheral glucose utilization than on increased endogenous production; (c) total insulin binding on isolated adipocytes is not significantly affected; (d) insulin resistance is primarily the outcome of postreceptor defect (impaired glucose transport).     

Mechanisms of glucagon secretion during insulin-induced hypoglycemia in man. Role of the beta cell and arterial hyperinsulinemia

To elucidate the mechanisms controlling the response of glucagon to hypoglycemia, a vital component of the counterregulatory hormonal response, the role of intraislet insulin was studied in seven normal subjects and five subjects with insulin-dependent diabetes mellitus (IDDM) (of less than 15-mo duration). In the normal subjects, hypoglycemia (arterial plasma glucose [PG] 53 +/- 3 mg/dl) induced by an intravenous insulin infusion (30 mU/m2 X min for 1 h, free immunoreactive insulin [FIRI] 58 +/- 2 microU/ml) elicited a 100% fall in insulin secretion and an integrated rise in glucagon of 7.5 ng/ml per 120 min. When endogenous insulin secretion was suppressed by congruent to 50 or congruent to 85% by a hyperinsulinemic-euglycemic clamp (FIRI 63 +/- 1.5 or 147 +/- 0.3 microU/ml, respectively) before hypoglycemia, the alpha cell responses to hypoglycemia were identical to those of the control study. When the endogenous insulin secretion was stimulated by congruent to 100% (hyperinsulinemic-hyperglycemic clamp, FIRI 145 +/- 1.5 microU/ml, PG 132 +/- 2 mg/dl) before hypoglycemia, the alpha cell responses to the hypoglycemia were also superimposable on those of the control study. Finally, in C-peptide negative diabetic subjects made euglycemic by a continuous overnight intravenous insulin infusion, the alpha cell responses to hypoglycemia were comparable to those of normal subjects despite absent beta cell secretion, and were not affected by antecedent hyperinsulinemia (hyperinsulinemic-euglycemic clamp for 2 h, FIRI 61 +/- 2 microU/ml). These results indicate that the glucagon response to insulin-induced hypoglycemia is independent of the level of both endogenous intraislet and exogenous arterial insulin concentration in normal man, and that this response may be normal in the absence of endogenous insulin secretion, in contrast to earlier reports. Thus, loss of beta cell function is not responsible for alpha cell failure during insulin-induced hypoglycemia in IDDM.     

Quantitative study of insulin secretion and clearance in normal and obese subjects.

The secretion and hepatic extraction of insulin were compared in 14 normal volunteers and 15 obese subjects using a previously validated mathematical model of insulin secretion and rate constants for C-peptide derived from analysis of individual decay curves after intravenous bolus injections of biosynthetic human C-peptide. Insulin secretion rates were substantially higher than normal in the obese subjects after an overnight fast (86.7 +/- 7.1 vs. 50.9 +/- 4.8 pmol/m2 per min, P less than 0.001, mean +/- SEM), over a 24-h period on a mixed diet (279.6 +/- 24.2 vs. 145.8 +/- 8.8 nmol/m2 per 24 h, P less than 0.001), and during a hyperglycemic intravenous glucose infusion (102.2 +/- 10.8 vs. 57.2 +/- 2.8 nmol/m2 per 180 min, P less than 0.001). Linear regression analysis revealed a highly significant relationship between insulin secretion and body mass index. Basal hepatic insulin extraction was not significantly different in the normal and obese subjects (53.1 +/- 3.8 vs. 51.6 +/- 4.0%). In the normal subjects, fasting insulin did not correlate with basal hepatic insulin extraction, but a significant negative correlation between fasting insulin and hepatic insulin extraction was seen in obesity (r = -0.63, P less than 0.02). This finding reflected a higher extraction in the six obese subjects with fasting insulin levels within the range of the normal subjects than in the nine subjects with elevated fasting insulin concentrations (61 +/- 3 vs. 45 +/- 6%, P less than 0.05). During the hyperglycemic clamp, the insulin secretion rate increased to an average maximum of 6.2-fold over baseline in the normal subjects and 5.8-fold in the obese subjects. Over the same time, the peripheral insulin concentration increased 14.1-fold over baseline in the normals and 16.6-fold over baseline in the obese, indicating a reduction in the clearance of endogenously secreted insulin. Although the fall in insulin clearance tended to be greater in the obese subjects, the differences between the two groups were not statistically significant. Thus, under basal, fasting conditions and during ingestion of a mixed diet, the hyperinsulinemia of obesity results predominantly from increased insulin secretion. In patients with more marked basal hyperinsulinemia and during intense stimulation of insulin secretion, a reduction in insulin clearance may contribute to the greater increase in peripheral insulin concentrations that are characteristic of the obese state.+     

Study of insulin metabolism in hyperthyroid patients

Hyperthyroidism is associated with degradation of carbohydrate metabolism. The insulin metabolism in 12 hyperthyroid patients is compared with 10 control subjects. The patients were connected to an artificial beta cell (Biostator GCIIS Miles) for two hours of insulin infusion (40 mU/m2/mn) while glycemia was maintained at its basal level by a modulated glucose infusion. Blood samples were taken, every 15 minutes for insulin and C peptide dosage. In control subjects the insulin steady state level was 93.3 +/- 5 microU/ml whereas this ranged from 42 +/- 3.4 microU/ml to 68 +/- 3.9 microU/ml in hyperthyroid patients. After treatment the insulin level was not quite normal, and ranged from 52 +/- 4.8 microU/ml to 82.2 +/- 9 microU/ml. A glucose intake not corresponding to the same insulin steady state is not therefore to be interpreted. Here there is no evidence of a correlation between the percentage decrease in the insulin test level and the thyroid hormone levels. An impairment of insulin metabolism is suggested in hyperthyroid patients, which might contribute to the decrease in carbohydrate tolerance.     

Practical aspects in performing the glucagon test in the measurement of C-peptide secretion in diabetic patients

The secretion of plasma C-peptide after intravenous glucagon stimulation was studied in 15 insulin-treated diabetic patients with onset of diabetes after the age of 30. The mean stimulation of C-peptide secretion caused by glucagon given in the fasting state and by a standardized breakfast were similar. Low blood glucose values (less than 3.5 mmol/l) were found to suppress the stimulating action of glucagon on the pancreas almost completely. When the glucagon test was performed 1.5 hours after a standardized breakfast, the mean concentration of plasma C-peptide was 62% higher than in the test in the fasting state, showing that the stimulating actions of glucagon and breakfast on the secretion of insulin are additive. The results indicate that when determining the level of plasma C-peptide after stimulation with glucagon, in order to distinguish between insulin-dependent and non-insulin-dependent diabetic patients, it is critical to take into account the consequence of low blood glucose values and to standardize the test conditions in regard to pre-test meals.     

Beta-cell function in mild type 2 diabetic patients: effects of 6-month glucose lowering with nateglinide

OBJECTIVE: We studied the effects of the oral insulin secretagogue nateglinide on insulin secretion using a modeling approach to obtain beta-cell function parameters from a meal test and examined the impact of the beta-cell improvement on glucose tolerance. RESEARCH DESIGN AND METHODS: Mild type 2 diabetic men and women (n = 108; fasting glucose 7.0-8.3 mmol/l) on diet treatment alone randomly received 30, 60, or 120 mg nateglinide or placebo for 24 weeks. Beta-cell function parameters were derived by modeling (based on C-peptide deconvolution) from a standardized meal test at baseline and after 24 weeks of treatment. RESULTS: The baseline demographic and metabolic characteristics of the four groups were similar. Nateglinide treatment resulted in dose-dependent reductions in the mean postprandial glucose response and at the 120-mg dose in fasting glucose. Fasting or total insulin secretion during the meal were not different. In contrast, we found differences in the model parameters. Rate sensitivity (expressing early insulin secretion when glucose is rising) was significantly enhanced at 24 weeks with the lowest nateglinide dose, with no further stimulation at higher doses. Early potentiation (expressing an initial insulin secretion enhancement), glucose sensitivity (the slope of the glucose-insulin secretion relationship), and insulin secretion at a fixed- reference 7-mmol/l glucose concentration all showed a trend toward increasing, with increasing nateglinide dose, and were significantly greater than placebo at the 120-mg dose. In multiple regression analyses, changes in rate sensitivity, glucose sensitivity, and potentiation all contributed to the observed glucose changes. CONCLUSIONS: The model-derived parameters are sensitive measures of beta-cell function, showing improvements after nateglinide treatment and predicting changes in glucose tolerance.     

Hyperglucagonemia and insulin-mediated glucose metabolism.

The effect of chronic physiologic hyperglucagonemia on basal and insulin-mediated glucose metabolism was evaluated in normal subjects, using the euglycemic insulin clamp technique (+50, +100, and +500 microU/ml). After glucagon infusion fasting glucose increased from 76 +/- 4 to 93 +/- 2 mg/dl and hepatic glucose production (HGP) rose from 1.96 +/- 0.08 to 2.25 +/- 0.08 mg/kg X min (P less than 0.001). Basal glucose oxidation after glucagon increased (P less than 0.05) and correlated inversely with decreased free fatty acid concentrations (r = -0.94; P less than 0.01) and decreased lipid oxidation (r = -0.75; P less than 0.01). Suppression of HGP and stimulation of total glucose disposal were impaired at each insulin step after glucagon (P less than 0.05-0.01). The reduction in insulin-mediated glucose uptake was entirely due to diminished non-oxidative glucose utilization. Glucagon infusion also caused a decrease in basal lipid oxidation and an enhanced ability of insulin to inhibit lipid oxidation and augment lipid synthesis. These results suggest that hyperglucagonemia may contribute to the disturbances in glucose and lipid metabolism in some diabetic patients.