Insulin production rate following glucose ingestion estimated by splanchnic C-peptide output in normal man

Kinetics of insulin and C-peptide and estimation of prehepatic insulin secretion rates after intravenous glucose stimulation using arterial versus venous blood sampling in healthy males

An intravenous glucose-infusion of 0.3 g glucose per Kg body weight was administered over 1 min in nine healthy males with simultaneous blood sampling from the hepatic vein, femoral artery and a peripheral vein. Insulin secretion rates (ISR) were determined by the Eaton method and the ISEC method using C-peptide concentrations from arterial and peripheral venous blood. First phase (0-10 min), second phase (10-60 min), and total insulin secretion (0-60 min) were calculated as the incremental areas (iAUC) above baseline. The primary endpoint was first phase insulin response. The first phase insulin response in artery and venous blood did not differ with the Eaton method (p = 0.25), but was significantly greater with the ISEC method in arterial compared with venous blood (p < 0.05). The first phase insulin responses did not differ between methods in artery (p = 0.73) or venous blood (p = 0.73). The first phase responses of insulin and C-peptide were significant higher in the hepatic vein compared with those in the artery (p < 0.05) and peripheral vein (p < 0.05) but did not differ significantly between the artery compared with the peripheral vein for insulin (p = 0.09) or C-peptide (p = 0.26). Prehepatic insulin secretion rates did not differ between the Eaton and ISEC methods, but with the ISEC method the first phase insulin response was significantly greater in arterial compared with venous blood. The first phase insulin response differs when calculated from plasma insulin or C-peptide and depends on sample sites.

Use of c-peptide as a measure of cephalic phase insulin release in humans

Cephalic phase insulin release (CPIR) is a rapid pulse of insulin secreted within minutes of food-related sensory stimulation. Understanding the mechanisms underlying CPIR in humans has been hindered by its small observed effect size and high variability within and between studies. One contributing factor to these limitations may be the use of peripherally measured insulin as an indicator of secreted insulin, since a substantial portion of insulin is metabolized by the liver before delivery to peripheral circulation. Here, we investigated the use of c-peptide, which is co-secreted in equimolar amounts to insulin from pancreatic beta cells, as a proxy for insulin secretion during the cephalic phase period. Changes in insulin and c-peptide were monitored in 18 adults over two repeated sessions following oral stimulation with a sucrose-containing gelatin stimulus. We found that, on average, insulin and c-peptide release followed a similar time course over the cephalic phase period, but that c-peptide showed a greater effect size. Importantly, when insulin and c-peptide concentrations were compared across sessions, we found that changes in c-peptide were significantly correlated at the 2 min (r = 0.50, p = 0.03) and 4 min (r = 0.65, p = 0.003) time points, as well as when participants' highest c-peptide concentrations were considered (r = 0.64, p = 0.004). In contrast, no significant correlations were observed for changes in insulin measured from the sessions (r = -0.06-0.35, p > 0.05). Herein, we detail the individual variability of insulin and c-peptide concentrations measured during the cephalic phase period, and identify c-peptide as a valuable metric for insulin secretion alongside insulin concentrations when investigating CPIR.

C-peptide enhances glucagon secretion in response to hyperinsulinemia under euglycemic and hypoglycemic conditions

Several studies have associated the presence of residual insulin secretion capability (also referred to as being C-peptide positive) with lower risk of insulin-induced hypoglycemia in patients with type 1 diabetes (T1D), although the reason is unclear. We tested the hypothesis that C-peptide infusion would enhance glucagon secretion in response to hyperinsulinemia during euglycemic and hypoglycemic conditions in dogs (5 male/4 female). After a 2-hour basal period, an intravenous (IV) infusion of insulin was started, and dextrose was infused to maintain euglycemia for 2 hours. At the same time, an IV infusion of either saline (SAL) or C-peptide (CPEP) was started. After this euglycemic period, the insulin and SAL/CPEP infusions were continued for another 2 hours, but the glucose was allowed to fall to approximately 50 mg/dL. In response to euglycemic-hyperinsulinemia, glucagon secretion decreased in SAL but remained unchanged from the basal period in CPEP condition. During hypoglycemia, glucagon secretion in CPEP was 2 times higher than SAL, and this increased net hepatic glucose output and reduced the amount of exogenous glucose required to maintain glycemia. These data suggest that the presence of C-peptide during IV insulin infusion can preserve glucagon secretion during euglycemia and enhance it during hypoglycemia, which could explain why T1D patients with residual insulin secretion are less susceptible to hypoglycemia.

Assessment of functional outcome of patients undergoing surgery for chronic pancreatitis: A prospective study

Backgrounds/Aims

This study was done with the aim of assessing impact of surgery for chronic pancreatitis on exocrine and endocrine functions, quality of life and pain relief of patients.

Methods

35 patients of chronic pancreatitis who underwent surgery were included. Exocrine function assessed with fecal fat globule estimation and endocrine function assessed with glycated haemoglobin (HbA1C), fasting plasma glucose (FPG), Insulin and C-peptide levels. Percentage (%) beta cell function by homeostatic model assessment (HOMA) was determined using web-based calculator. Quality of life (QOL) and pain assessment was done using Short form survey (SF-36) questionnaire and Izbicki scores respectively. Follow up done till 3 months following surgery.

Results

Endocrine insufficiency was noted in 13 (37%) patients in the postoperative period compared to 17 (49%) patients preoperatively (p=0.74). Exocrine insufficiency was detected in 11 (32%) patients postoperatively compared to 8 (23%) patients preoperatively, with denovo insufficiency noted in 3 (8%) patients (p<0.05). The mean Izbicki score at 3 months postoperatively was remarkably lower compared to preoperative score (29.3±14.3 vs. 60.6±12.06; p<0.05). QOL at 3 months following surgery for chronic pancreatitis was significantly better than preoperative QOL (50.24±22.16 vs. 69.48±20.81; p<0.05).

Conclusions

Significant pain relief and improvement in quality of life among patients of chronic pancreatitis following surgery. However, worsening of exocrine function with only clinical improvement of endocrine function was also noted.

Hepatic Insulin Clearance in Regulation of Systemic Insulin Concentrations-Role of Carbohydrate and Energy Availability

Hyperinsulinemia is the hallmark of insulin resistance in obesity, and the relative importance of insulin clearance, insulin resistance, and insulin hypersecretion has been widely debated. On the basis of recent experimental evidence, we summarize existing evidence to suggest hepatic insulin clearance as a major and immediate regulator of systemic insulin concentrations responding within days to altered dietary energy and, in particular, carbohydrate intake. Hepatic insulin clearance seems to be closely associated with opposite alterations in hepatic lipid content and glucose production, providing a potential mechanistic link to hepatic insulin sensitivity. The molecular regulation of insulin clearance in the liver is likely to involve changes in insulin binding and receptor internalization in response to the dietary alterations, the molecular mechanisms of which await further research.

Variability of Directly Measured First-Pass Hepatic Insulin Extraction and Its Association With Insulin Sensitivity and Plasma Insulin

Although the β-cells secrete insulin, the liver, with its first-pass insulin extraction (FPE), regulates the amount of insulin allowed into circulation for action on target tissues. The metabolic clearance rate of insulin, of which FPE is the dominant component, is a major determinant of insulin sensitivity (SI). We studied the intricate relationship among FPE, SI, and fasting insulin. We used a direct method of measuring FPE, the paired portal/peripheral infusion protocol, where insulin is infused stepwise through either the portal vein or a peripheral vein in healthy young dogs (n = 12). FPE is calculated as the difference in clearance rates (slope of infusion rate vs. steady insulin plot) between the paired experiments. Significant correlations were found between FPE and clamp-assessed SI (r_s = 0.74), FPE and fasting insulin (r_s = -0.64), and SI and fasting insulin (r_s = -0.67). We also found a wide variance in FPE (22.4-77.2%; mean ± SD 50.4 ± 19.1) that is reflected in the variability of plasma insulin (48.1 ± 30.9 pmol/L) and SI (9.4 ± 5.8 × 10⁴ dL · kg^-1 · min^-1 · [pmol/L]^-1). FPE could be the nexus of regulation of both plasma insulin and SI.

Insulin therapy for type 2 diabetes - are we there yet? The d-Nav® story

Insulin replacement therapy is mostly used by patients with type 2 diabetes who become insulin deficient and have failed other therapeutic options. They comprise about a quarter of those with diabetes, endures the majority of the complications and consumes the majority of the resources. Adequate insulin replacement therapy can prevent complications and reduce expenses, as long as therapy goals are achieved and maintained. Sadly, these therapy goals are seldom achieved and outcomes have not improved for decades despite advances in pharmacotherapy and technology.

There is a growing recognition that the low success rate of insulin therapy results from intra-individual and inter-individual variations in insulin requirements. Total insulin requirements per day vary considerably between patients and constantly change without achieving a steady state. Thus, the key element in effective insulin therapy is unremitting and frequent dosage adjustments that can overcome those dynamics. In practice, insulin adjustments are done sporadically during outpatient clinic. Due to time constraints, providers are not able to deliver appropriate insulin dosage optimization.

The d-Nav® Insulin Guidance Service has been developed to provide appropriate insulinization in insulin users without increasing the burden on healthcare systems. It relies on dedicated clinicians and a spectrum of technological solutions. Patients are provided with a handheld device called d-Nav® which advises them what dose of insulin to administer during each injection and automatically adjust insulin dosage when needed. The d-Nav care specialists periodically follow-up with users through telephone calls and in-person consultations to bestow user confidence, correct usage errors, triage, and identify uncharacteristic clinical courses.

The following review provide details about the service and its clinical outcomes.

Deterioration of insulin release rate response to glucose during oral glucose tolerance test is associated with an increased risk of incident diabetes in normal glucose tolerance subjects

β-Cell dedifferentiation, characterized by loss of glucose sensitivity (β-cell glucose sensitivity [βCGS]), has been reported to play an important role in the development of type 2 diabetes (T2D). Traditionally, βCGS was derived from C-peptide-based method. However, C-peptide was not routinely examined in normal subjects and diabetes never treated with insulin. Thus, the aim of the study was to evaluate the use of insulin in oral glucose tolerance test (OGTT) in estimation of β-cell glucose response ability. A total of 1,599 subjects including normal glucose tolerance (NGT), impaired glucose tolerance (IGT) and T2D were included in the study. A subgroup of NGT subjects (n = 591) were followed up for an average duration of 56.88 ± 20.76 months. Insulin release rate (IRR_INS ) in the function of glucose (IRR_INS response to glucose [IRRG]) during OGTT was compared with βCGS. Both βCGS derived from C-peptide by deconvolution approach and IRRG by insulin release progressively declined from NGT to IGT and T2D. Both βCGS and IRRG were associated with deposit of first-phase insulin secretion (DI_1st ). After 56.88 ± 20.76 months, 32 (5.41%) NGT subjects had developed T2D. NGT subjects who progressed to diabetes after follow-up had lower IRRG and DI_1st levels than those who did not (P < 0.01). Furthermore, multiple logistic regression analyses showed that decreased IRRG was a significant independent risk predictor for future diabetes after adjustment of age, body mass index (BMI), homeostasis model assessment (HOMA)-insulin resistance, DI_1st and family history. NGT subjects with decreased IRRG during OGTT had defective early insulin secretion and were at higher risk of developing diabetes. IRRG could be a useful T2D predictor in NGT subjects. © 2017 IUBMB Life, 69(9):756-766, 2017.

Diagnosis of insulinoma using the ratios of serum concentrations of insulin and C-peptide to glucose during a 5-hour oral glucose tolerance test

The 72-hour fast test is the current standard for the diagnosis of insulinoma. However, to conduct this test patients require hospitalization due to the chance of severe hypoglycemic episodes. Thus, it is costly and stressful for the patient. An out-patient test would serve the patient better and be more economical. Our aim was to evaluate the value of insulin to glucose and C-peptide to glucose ratios during a prolonged 5-hour oral glucose tolerance test (5-hour OGTT) in qualitative diagnosis of insulinoma, and to identify the optimal threshold for clinical screening. Initially, 15 subjects with pathological insulinoma and 12 control subjects with reactive hypoglycemia were enrolled in the study. A further 75 subjects with symptoms of hypoglycemia as a chief complaint at their initial clinic visit were subsequently screened. Serum insulin, C- peptide levels and blood glucose were quantified after a 5-hour OGTT in all participants and the ratios of serum concentrations of insulin and C-peptide to glucose were calculated. Subjects with insulinoma had significantly different insulin-to-glucose and C-peptide-to-glucose ratios from reactive hypoglycemia at the times of fasting, 4-hour post glucose load and 5-hour post glucose load. Higher specificity (73.08%) and sensitivity (82.67%) were achieved with the combined insulin-to-glucose ratio at the 5-hour post load and the C-peptide-to-glucose ratio at fasting. In combination, ratios of insulin and C-peptide release relative to blood glucose levels, measured during a 5-hour OGTT, may have important clinical value in the diagnosis of insulinoma.

TCF7L2 Genotype and α-Cell Function in Humans Without Diabetes

The diabetes-associated allele in TCF7L2 increases the rate of conversion to diabetes; however, the mechanism by which this occurs remains elusive. We hypothesized that the diabetes-associated allele in this locus (rs7903146) impairs insulin secretion and that this defect would be exacerbated by acute free fatty acid (FFA)-induced insulin resistance. We studied 120 individuals of whom one-half were homozygous for the diabetes-associated allele TT at rs7903146 and one-half were homozygous for the protective allele CC. After a screening examination during which glucose tolerance status was determined, subjects were studied on two occasions in random order while undergoing an oral challenge. During one study day, FFA was elevated by infusion of Intralipid plus heparin. On the other study day, subjects received the same amount of glycerol as present in the Intralipid infusion. β-Cell responsivity indices were estimated with the oral C-peptide minimal model. We report that β-cell responsivity was slightly impaired in the TT genotype group. Moreover, the hyperbolic relationship between insulin secretion and β-cell responsivity differed significantly between genotypes. Subjects also exhibited impaired suppression of glucagon after an oral challenge. These data imply that a genetic variant harbored within the TCF7L2 locus impairs glucose tolerance through effects on glucagon as well as on insulin secretion.

Magnetic resonance imaging reveals altered distribution of hepatic fat in children with type 1 diabetes compared to controls

INTRODUCTION

Children with type 1 diabetes have been identified as a risk group for non-alcoholic fatty liver disease (NAFLD). The aim was to compare total hepatic fat fraction and fat distribution across Couinaud segments in children with type 1 diabetes and controls and the relation of hepatic fat to plasma and anthropometric parameters.

METHODS

Hepatic fat fraction and fat distribution across Couinaud segments were measured with magnetic resonance imaging (MRI) in 22 children with type 1 diabetes and 32 controls. Blood tests and anthropometric data were collected.

RESULTS

No children had NAFLD. Children with type 1 diabetes had a slightly lower hepatic fat fraction (median 1.3%) than controls (median 1.8%), and their fat had a different segmental distribution. The fat fraction of segment V was the most representative of the liver as a whole. An incidental finding was that diabetes patients treated with multiple daily injections of insulin (MDI) had a fat distribution more similar to controls than patients with continuous subcutaneous insulin infusion (CSII).

CONCLUSIONS

In children with type 1 diabetes, NAFLD may be less common than recent studies have suggested. Children with type 1 diabetes may have a lower fat fraction and a different fat distribution in the liver than controls. Diabetes treatment with MDI or CSII may affect liver fat, but this needs to be confirmed in a larger sample of patients. The heterogeneity of hepatic fat infiltration may affect results when liver biopsy is used for diagnosing fatty liver.

Comparison of the physiological relevance of systemic vs. portal insulin delivery to evaluate whole body glucose flux during an insulin clamp

To understand the underlying pathology of metabolic diseases, such as diabetes, an accurate determination of whole body glucose flux needs to be made by a method that maintains key physiological features. One such feature is a positive differential in insulin concentration between the portal venous and systemic arterial circulation (P/S-IG). P/S-IG during the determination of the relative contribution of liver and extra-liver tissues/organs to whole body glucose flux during an insulin clamp with either systemic (SID) or portal (PID) insulin delivery was examined with insulin infusion rates of 1, 2, and 5 mU·kg(-1)·min(-1) under either euglycemic or hyperglycemic conditions in 6-h-fasted conscious normal rats. A P/S-IG was initially determined with endogenous insulin secretion to exist with a value of 2.07. During an insulin clamp, while inhibiting endogenous insulin secretion by somatostatin, P/S-IG remained at 2.2 with PID, whereas, P/S-IG disappeared completely with SID, which exhibited higher arterial and lower portal insulin levels compared with PID. Consequently, glucose disappearance rates and muscle glycogen synthetic rates were higher, but suppression of endogenous glucose production and liver glycogen synthetic rates were lower with SID compared with PID. When the insulin clamp was performed with SID at 2 and 5 mU·kg(-1)·min(-1) without managing endogenous insulin secretion under euglycemic but not hyperglycemic conditions, endogenous insulin secretion was completely suppressed with SID, and the P/S-IG disappeared. Thus, compared with PID, an insulin clamp with SID underestimates the contribution of liver in response to insulin to whole body glucose flux.

Reflections of a clinician on switch from human to analogue insulin treatment

The development of insulin therapy has not been stopped since the manufacturing of human insulin, because better mimic of physiological insulin response made it necessary to modify the human insulin molecule in order to create rapidly absorbing insulin analogues and 24-hour acting basal insulin analogues. Clinical observations indicate that the complete switch from human basal-bolus therapy to insulin analogues means not only “unit-for-unit” switch but it represents a transfer to an insulin therapy with different basal/bolus ratio as a result of different pharmacokinetic and pharmacodynamic properties of insulin and the level of insulin resistance of the patient. With reference to a case-history, the author presents his experience on a switch from human insulin to insulin analogue. Furthermore, the author summarizes data obtained from a few cases reported in international literature which draw the attention to the fact that the basal/bolus ratio should be adjusted individually, which may be the key for the success in the therapy in these cases. Orv. Hetil., 2012, 153, 1589–1593.

Insulin clearance is different in men and women

Insulin is often infused based upon total body weight (TBW) or fat-free mass (FFM) for glucose clamp protocols. We observed greater insulin concentrations in men than women using this approach and examined whether splanchnic insulin extraction accounts for the differences. Whole-body insulin clearance was measured during a pancreatic clamp study (somatostatin to inhibit islet hormone secretion) including 13 adults (6 men); and whole-body insulin clearance was measured during a euglycemic, hyperinsulinemic clamp study including 27 adults (13 men). Femoral artery and hepatic vein blood samples were collected to measure splanchnic insulin balance. For the pancreatic clamp study, insulin was infused at rates of 0.5, 1.0, and 2.0 mU/kg of TBW per minute; and for the euglycemic, hyperinsulinemic clamp study, insulin was infused at 2.5 mU/kg of FFM per minute. Significantly greater arterial insulin concentrations were found in men than women. Splanchnic plasma flow was similar in men and women in both protocols. Splanchnic insulin extraction and the fraction of infused insulin removed by splanchnic bed were significantly greater in men than in women. However, whole-body insulin clearance was greater in women than men. Infusing insulin per body weight or FFM results in higher plasma insulin concentrations in men than women. Splanchnic insulin extraction is greater in men, indicating that greater peripheral insulin clearance in women accounts for the sex differences we observed. This finding has implications for insulin clamp study design and raises the question of which tissues take up more insulin in women.

Hepatic steatosis in type 1 diabetes

Islet autoimmunity in type 1 diabetes results in the loss of the pancreatic β-cells. The consequences of insulin deficiency in the portal vein for liver fat are poorly understood. Under normal conditions, the portal vein provides 75% of the liver blood supply. Recent studies suggest that non-alcoholic fatty liver disease (NAFLD) may be more common in type 1 diabetes than previously thought, and may serve as an independent risk marker for some chronic diabetic complications. The pathogenesis of NAFLD remains obscure, but it has been hypothesized that hepatic fat accumulation in type 1 diabetes may be due to lipoprotein abnormalities, hyperglycemia-induced activation of the transcription factors carbohydrate response element-binding protein (ChREBP) and sterol regulatory element-binding protein 1c (SREBP-1c), upregulation of glucose transporter 2 (GLUT2) with subsequent intrahepatic fat synthesis, or a combination of these mechanisms. Novel approaches to non-invasive determinations of liver fat may clarify the consequences for liver metabolism when the pancreas has ceased producing insulin. This article aims to review the factors potentially contributing to hepatic steatosis in type 1 diabetes, and to assess the feasibility of using liver fat as a prognostic and/or diagnostic marker for the disease. It provides a background and a case for possible future studies in the field.

The incretin effect and secretion in obese and lean women with polycystic ovary syndrome: a pilot study

BACKGROUND

Insulin resistance is considered to play an important role in the pathogenesis of polycystic ovary syndrome (PCOS) and in the progression to type 2 diabetes. Recent reports concentrate on a possible relationship between incretin secretion and beta-cell function in PCOS. The aim of the present study is to investigate the incretin effect in obese and lean women with PCOS.

METHODS

Twenty women with PCOS and ten age-matched healthy women were recruited in the study. The oral glucose tolerance test (OGTT) and isoglycemic test were carried out on each participant after an overnight fast at 2-weeks interval. Plasma levels of insulin, glucose, C-peptide, glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide-1 (GLP-1) were assayed.

RESULTS

Obese women with PCOS demonstrated lower GIP concentrations (area under the curve [AUC]) in response to OGTT compared to the control group. The incretin effect was found significantly augmented in the obese women with PCOS compared to controls. This finding remained robust in the subgroup analysis including only body mass index (BMI)-matched healthy women.

CONCLUSIONS

Increased insulinotropic effect could counteract the blunted GIP response to OGTT in obese women with PCOS. It is suggested that the pathology of PCOS may also include impaired activity of the enteroinsular axis.

The role of hepatic fat accumulation in pathogenesis of non-alcoholic fatty liver disease (NAFLD)

Nonalcoholic fatty liver disease is increasingly regarded as a hepatic manifestation of metabolic syndrome, and the severity of nonalcoholic fatty liver disease seems to increase in parallel with other features of metabolic syndrome. Excess lipid accumulation in the liver cells is not only a mediator of Metabolic Syndrome and indicator of a lipid overload but also accompanied by a range of histological alterations varying from 'simple' steatosis to nonalcoholic steatohepatitis, with time progressing to manifest cirrhosis. Hepatocellular carcinoma may also occur in nonalcoholic steatohepatitis -related cirrhosis with a mortality rate similar to or worse than for cirrhosis associated with hepatitis C. This review summarizes the knowledge about the causal relationship between hepatic fat accumulation, insulin resistance, liver damage and the etiological role of hepatic fat accumulation in pathogenesis of extra- and intra-hepatic manifestations. Special emphasis is given suggestions of new targets treatment and prevention of nonalcoholic fatty liver disease.

Bone marrow as an alternative site for islet transplantation

The liver is the current site for pancreatic islet transplantation, but has many drawbacks due to immunologic and nonimmunologic factors. We asked whether pancreatic islets could be engrafted in the bone marrow (BM), an easily accessible and widely distributed transplant site that may lack the limitations seen in the liver. Syngeneic islets engrafted efficiently in the BM of C57BL/6 mice rendered diabetic by streptozocin treatment. For more than 1 year after transplantation, these animals showed parameters of glucose metabolism that were similar to those of nondiabetic mice. Islets in BM had a higher probability to reach euglycemia than islets in liver (2.4-fold increase, P = .02), showed a compact morphology with a conserved ratio between alpha and beta cells, and affected bone structure only very marginally. Islets in BM did not compromise hematopoietic activity, even when it was strongly induced in response to a BM aplasia-inducing infection with lymphocytic choriomeningitis virus. In conclusion, BM is an attractive and safe alternative site for pancreatic islet transplantation. The results of our study open a research line with potentially significant clinical impact, not only for the treatment of diabetes, but also for other diseases amenable to treatment with cellular transplantation.

Effect of liver fat on insulin clearance

A fatty liver is associated with fasting hyperinsulinemia, which could reflect either impaired insulin clearance or hepatic insulin action. We determined the effect of liver fat on insulin clearance and hepatic insulin sensitivity in 80 nondiabetic subjects [age 43 +/- 1 yr, body mass index (BMI) 26.3 +/- 0.5 kg/m(2)]. Insulin clearance and hepatic insulin resistance were measured by the euglycemic hyperinsulinemic (insulin infusion rate 0.3 mU.kg(-1).min(-1) for 240 min) clamp technique combined with the infusion of [3-(3)H]glucose and liver fat by proton magnetic resonance spectroscopy. During hyperinsulinemia, both serum insulin concentrations and increments above basal remained approximately 40% higher (P < 0.0001) in the high (15.0 +/- 1.5%) compared with the low (1.8 +/- 0.2%) liver fat group, independent of age, sex, and BMI. Insulin clearance (ml.kg fat free mass(-1).min(-1)) was inversely related to liver fat content (r = -0.52, P < 0.0001), independent of age, sex, and BMI (r = -0.37, P = 0.001). The variation in insulin clearance due to that in liver fat (range 0-41%) explained on the average 27% of the variation in fasting serum (fS)-insulin concentrations. The contribution of impaired insulin clearance to fS-insulin concentrations increased as a function of liver fat. This implies that indirect indexes of insulin sensitivity, such as homeostatic model assessment, overestimate insulin resistance in subjects with high liver fat content. Liver fat content correlated significantly with fS-insulin concentrations adjusted for insulin clearance (r = 0.43, P < 0.0001) and with directly measured hepatic insulin sensitivity (r = -0.40, P = 0.0002). We conclude that increased liver fat is associated with both impaired insulin clearance and hepatic insulin resistance. Hepatic insulin sensitivity associates with liver fat content, independent of insulin clearance.

Reduction of hepatic insulin clearance after oral glucose ingestion is not mediated by glucagon-like peptide 1 or gastric inhibitory polypeptide in humans

Changes in hepatic insulin clearance can occur after oral glucose or meal ingestion. This has been attributed to the secretion and action of gastric inhibitory polypeptide (GIP) and glucagon-like peptide (GLP)-1. Given the recent availability of drugs based on incretin hormones, such clearance effects may be important for the future treatment of type 2 diabetes. Therefore, we determined insulin clearance in response to endogenously secreted and exogenously administered GIP and GLP-1. Insulin clearance was estimated from the molar C-peptide-to-insulin ratio calculated at basal conditions and from the respective areas under the curve after glucose, GIP, or GLP-1 administration. Oral glucose administration led to an approximately 60% reduction in the C-peptide-to-insulin ratio (P < 0.0001), whereas intravenous glucose administration had no effect (P = 0.09). The endogenous secretion of GIP or GLP-1 was unrelated to the changes in insulin clearance. The C-peptide-to-insulin ratio was unchanged after the intravenous administration of GIP or GLP-1 in the fasting state (P = 0.27 and P = 0.35, respectively). Likewise, infusing GLP-1 during a meal course did not alter insulin clearance (P = 0.87). An inverse nonlinear relationship was found between the C-peptide-to-insulin ratio and the integrated insulin levels after oral and during intravenous glucose administration. Insulin clearance is reduced by oral but not by intravenous glucose administration. Neither GIP nor GLP-1 has significant effects on insulin extraction. An inverse relationship between insulin concentrations and insulin clearance suggests that the secretion of insulin itself determines the rate of hepatic insulin clearance.

Intrahepatic transplanted islets in humans secrete insulin in a coordinate pulsatile manner directly into the liver

Intrahepatic islet transplantation is an experimental therapy for type 1 diabetes. In the present studies, we sought to address the following questions: 1) In humans, do intrahepatic transplanted islets reestablish coordinated puslatile insulin secretion? and 2) To what extent is insulin secreted by intrahepatic transplanted islets delivered to the hepatic sinusoids (therefore effectively restoring a portal mode of insulin delivery) versus delivered to the hepatic central vein (therefore effectively providing a systemic form of insulin delivery)? To address the first question, we examined insulin concentration profiles in the overnight fasting state and during a hyperglycemic clamp ( approximately 150 mg/dl) in 10 recipients of islet transplants and 10 control subjects. To address the second question, we measured first-pass hepatic insulin clearance in two recipients of islet autografts after pancreatectomy for pancreatitis versus five control subjects by direct catheterization of the hepatic vein. We report that coordinate pulsatile insulin secretion is reestablished in islet transplant recipients and that glucose-mediated stimulation of insulin secretion is accomplished by amplification of insulin pulse mass. Direct hepatic catheterization studies revealed that intrahepatic islets in humans do deliver insulin directly to the hepatic sinusoid because approximately 80% of the insulin is extracted during first pass. In conclusion, intrahepatic islet transplantation effectively restores the liver to pulsatile insulin delivery.

Serum C-peptide levels and breast cancer risk: results from the European Prospective Investigation into Cancer and Nutrition (EPIC)

It has been hypothesized that chronic hyperinsulinemia, a major metabolic consequence of physical inactivity and excess weight, might increase breast cancer risk by direct effects on breast tissue or indirectly by increasing bioavailable levels of testosterone and estradiol. Within the European Prospective Investigation into Cancer and Nutrition (EPIC), we measured serum levels of C-peptide--a marker for pancreatic insulin secretion--in a total of 1,141 incident cases of breast cancer and 2,204 matched control subjects. Additional measurements were made of serum sex hormone binding globulin (SHBG) and sex steroids. Conditional logistic regression models were used to estimate breast cancer risk for different levels of C-peptide. C-peptide was inversely correlated with SHBG and hence directly correlated with free testosterone among both pre and postmenopausal women. C-peptide and free estradiol also correlated positively, but only among postmenopausal women. Elevated serum C-peptide levels were associated with a nonsignificant reduced risk of breast cancer diagnosed up to the age of 50 years [odds ratio (OR)=0.70, (95% confidence interval (CI), 0.39-1.24); ptrend=0.05]. By contrast, higher levels of C-peptide were associated with an increase of breast cancer risk among women above 60 years of age, however only among those women who had provided a blood sample under nonfasting conditions [OR=2.03, (95% CI, 1.20-3.43); ptrend=0.01]. Our results do not support the hypothesis that chronic hyperinsulinemia generally increases breast cancer risk, independently of age. Nevertheless, among older, postmenopausal women, hyperinsulinemia might contribute to increasing breast cancer risk.

Pulsatile insulin secretion dictates systemic insulin delivery by regulating hepatic insulin extraction in humans

In health, insulin is secreted in discrete pulses into the portal vein, and the regulation of the rate of insulin secretion is accomplished by modulation of insulin pulse mass. Several lines of evidence suggest that the pattern of insulin delivery by the pancreas determines hepatic insulin clearance. In previous large animal studies, the amplitude of insulin pulses was related to the extent of insulin clearance. In humans (and in large animals), the amplitude of insulin oscillations is approximately 100-fold higher in the portal vein than in the systemic circulation, despite only a fivefold dilution, implying preferential hepatic extraction of insulin pulses. In the present study, by direct hepatic vein sampling in healthy humans, we sought to establish the extent of first-pass hepatic insulin extraction and to determine whether the pattern of insulin secretion (insulin pulse mass and amplitude) dictates the hepatic insulin clearance and thereby delivery of insulin to extrahepatic insulin-responsive tissues. Five nondiabetic subjects (two men and three women, mean age 32 years [range 25-39], BMI 24.9 kg/m(2) [21.2-27.1]) participated. Insulin and C-peptide delivery from the splanchnic bed was measured in basal overnight-fasted state and during a glucose infusion of 2 mg . kg(-1) . min(-1) by simultaneous sampling from the hepatic vein and an arterialized vein along with direct estimation of splanchnic blood flow. Fractional insulin extraction was calculated from the difference between the C-peptide and insulin delivery rates from the liver. The time patterns of insulin concentrations and hepatic insulin clearance were analyzed by deconvolution and Cluster analysis, respectively. Cross-correlation analysis was used to relate C-peptide secretion and insulin clearance. Glucose infusion increased peripheral glucose concentrations from 5.4 +/- 0.1 to 6.4 +/- 0.4 mmol/l (P < 0.05). Likewise, insulin and C-peptide concentrations increased during glucose infusion (P < 0.05). Hepatic insulin clearance increased with glucose infusion (1.06 +/- 0.18 vs. 2.55 +/- 0.38 pmol . kg(-1) . min(-1); P < 0.01), but fractional hepatic insulin clearance was stable (78.2 +/- 4.4 vs. 84 0. +/- 3.9%, respectively; P = 0.18). Insulin secretory-burst mass rose during glucose infusion (P < 0.05), whereas the interburst interval remained unchanged (4.4 +/- 0.2 vs. 4.5 +/- 0.3 min; P = 0.36). Cluster analysis identified an oscillatory pattern in insulin clearance, with peaks occurring approximately every 5 min. Cross-correlation analysis between prehepatic C-peptide secretion and hepatic insulin clearance demonstrated a significant positive association without detectable (<1 min) time lag. Insulin secretory-burst mass strongly predicted insulin clearance (r = 0.81, P = 0.0043). In conclusion, in humans, approximately 80% of insulin is extracted during the first liver passage. The liver rapidly responds to fluctuations in insulin secretion, preferentially extracting insulin delivered in pulses. The mass (and therefore amplitude) of insulin pulses traversing the liver is the predominant determinant of hepatic insulin clearance. Therefore, through this means, the pulse mass of insulin release dictates both hepatic (directly) as well as extra-hepatic (indirectly) insulin delivery. These findings emphasize the dual role of the liver and pancreas and their relationship mediated through magnitude of insulin pulse mass in regulating the quantity and pattern of systemic insulin delivery.

Alterations in postprandial hepatic glycogen metabolism in type 2 diabetes

Decreased skeletal muscle glucose disposal and increased endogenous glucose production (EGP) contribute to postprandial hyperglycemia in type 2 diabetes, but the contribution of hepatic glycogen metabolism remains uncertain. Hepatic glycogen metabolism and EGP were monitored in type 2 diabetic patients and nondiabetic volunteer control subjects (CON) after mixed meal ingestion and during hyperglycemic-hyperinsulinemic-somatostatin clamps applying 13C nuclear magnetic resonance spectroscopy (NMRS) and variable infusion dual-tracer technique. Hepatocellular lipid (HCL) content was quantified by 1H NMRS. Before dinner, hepatic glycogen was lower in type 2 diabetic patients (227 +/- 6 vs. CON: 275 +/- 10 mmol/l liver, P < 0.001). After meal ingestion, net synthetic rates were 0.76 +/- 0.16 (type 2 diabetic patients) and 1.36 +/- 0.15 mg x kg(-1) x min(-1) (CON, P < 0.02), resulting in peak concentrations of 283 +/- 15 and 360 +/- 11 mmol/l liver. Postprandial rates of EGP were approximately 0.3 mg x kg(-1) x min(-1) (30-170 min; P < 0.05 vs. CON) higher in type 2 diabetic patients. Under clamp conditions, type 2 diabetic patients featured approximately 54% lower (P < 0.03) net hepatic glycogen synthesis and approximately 0.5 mg x kg(-1) x min(-1) higher (P < 0.02) EGP. Hepatic glucose storage negatively correlated with HCL content (R = -0.602, P < 0.05). Type 2 diabetic patients exhibit 1) reduction of postprandial hepatic glycogen synthesis, 2) temporarily impaired suppression of EGP, and 3) no normalization of these defects by controlled hyperglycemic hyperinsulinemia. Thus, impaired insulin sensitivity and/or chronic glucolipotoxicity in addition to the effects of an altered insulin-to-glucagon ratio or increased free fatty acids accounts for defective hepatic glycogen metabolism in type 2 diabetic patients.

Renal extraction of insulin and C-peptide in man before and after a glucose meal

It was recently shown that the early rise in arterial insulin concentration after an oral glucose meal is largely because of a decreased extraction of the hormone. The kidney is a major site for extraction of insulin and C-peptide. We therefore measured the renal extraction of insulin and C-peptide in eight healthy individuals before and after ingestion of 75 g of glucose. Arterial, renal venous and hepatic venous catheters were inserted. Splanchnic and renal plasma flow were measured, as well as arterial, hepatic venous and renal venous concentrations of insulin and C-peptide. Renal fractional extraction of insulin increased significantly, from 21% to a maximum of 48% after the meal while the renal fractional extraction of C-peptide did not change significantly. Renal blood flow decreased slightly but significantly after the meal. It is concluded that renal fractional extraction of insulin increases and that renal blood flow decreases after a glucose meal.

The circulating hormonal milieu of the endocrine pancreas in healthy individuals, organ donors, and the isolated perfused human pancreas

Although basal circulating levels of individual islet cell hormones have been measured, few studies compared the molar ratios of the major hormones secreted by the endocrine pancreas. This study examined the basal levels of four major islet hormones: insulin, C-peptide (C-P), glucagon (G), and pancreatic polypeptide (PP) in normal subjects, in organ donors with brain death, and in the isolated perfused human pancreas. Basal blood samples were taken from normal, fasted control subjects (NCs). Pancreata were obtained from 17 organ donors (ODs) with donor portal vein (DPV) and radial arterial (DRA) blood samples taken before organ procurement. Single-pass perfusion was performed on the procured pancreata, and after rewarming and equilibration, basal samples were collected from the splenic vein (SV) for 30 min. Radioimmunoassays of insulin, C-P, G, and PP were performed on all samples, and basal levels of all hormones were expressed as a common unit, femtomoles per milliliter. The data suggest that in the basal state, these four major islet hormones circulate in a relatively constant molar ratio. The ratio of the hormones is altered in brain death and with in vitro perfusion of the pancreas. The isolated perfused human pancreas secretes a relatively constant molar ratio of these hormones; however, this ratio is markedly different from the circulating ratio seen in either the NC group or the OD group. We conclude that a relatively constant hormonal milieu is secreted from the normal endocrine pancreas, and this hormonal milieu is altered after brain death and with isolation and perfusion of the human pancreas.

Pioglitazone enhances splanchnic glucose uptake as well as peripheral glucose uptake in non-insulin-dependent diabetes mellitus. AD-4833 Clamp-OGL Study Group

To evaluate the effect of pioglitazone on insulin resistance in non-insulin-dependent diabetes mellitus (NIDDM) patients, a double-blind placebo-controlled trial was carried out with 30 NIDDM patients. Twenty-one subjects, three on diet alone and 18 on sulfonylurea (SU), orally received 30 mg pioglitazone once daily for 12 weeks. Nine subjects, one on diet alone and eight on SU, received a matching placebo once daily for 12 weeks. Euglycemic (5.2 mmol/l) hyperinsulinemic (1200 pmol/l) clamp combined with an oral glucose load (OGL) was performed before and after 3-month treatment with pioglitazone or placebo to determine insulin-stimulated glucose disposal and splanchnic glucose uptake (SGU). No significant differences existed in the patients' characteristics, including age and body mass index, between the two study groups. The pioglitazone treatment increased the mean glucose infusion rate (GIR) prior to OGL from 8.2 +/- 2.2 to 9.2 +/- 2.0 mg/kg.min (mean +/- SD, P = 0.003) and increased the SGU rate from 28.5 +/- 19.4 to 59.4 +/- 27.1% (P = 0.010). The placebo treatment produced no significant changes in either GIR or SGU after treatment. A significant difference (P = 0.042) was observed in change of SGU between the pioglitazone and placebo treatment groups. In conclusion, the results indicate that pioglitazone is effective for ameliorating insulin resistance in NIDDM by enhancing SGU as well as peripheral glucose uptake.

Insulin resistance shows selective metabolic and hormonal targets in the elderly

There has been no simultaneous evaluation of different aspects of insulin action in ageing. We studied 12 elderly (77 +/- 2 years) and 12 young (26 +/- 1 years) subjects with normal glucose tolerance and matched for sex, body mass index, lean body mass (LBM), blood pressure and physical activity, using a euglycaemic-hyperinsulinaemic clamp at about 350 pmol L-1 in combination with [3H]-glucose infusion. In the elderly group, hepatic glucose production was normal, fasting serum insulin and C-peptide were significantly increased (P = 0.001) and glucose utilization (34.4 +/- 2.4 vs. 44.4 +/- 3.2 mumol kg-1 LBM min-1, P = 0.02) and the percentage maximal suppression of C-peptide (58 +/- 6% vs. 79 +/- 5%, P = 0.02) during the clamp were reduced. Fasting plasma free fatty acid (FFA) and glycerol levels were similar in the two groups, but their percentage maximal suppression during the clamp was reduced in the elderly group (FFA 45 +/- 5% vs. 77 +/- 6%, P = 0.001; glycerol 43 +/- 5% vs. 76 +/- 3%, P = 0.001). Branched-chain amino acids (valine, leucine, isoleucine) and glucagon levels were similar in the two groups, both while fasting and during the clamp. Thus, insulin resistance in ageing appears selective on glucose utilization, inhibition of lipolysis and feedback inhibition of the B-cell secretion.

Urine C-peptide and atherogenic risk factors in diabetes mellitus: relevance to "syndrome X"

The relation between the C-peptide concentration in twenty-four-hour urine specimens and atherogenic risk factors was investigated in 38 patients with noninsulin-dependent diabetes mellitus in an attempt to determine the significance of urine C-peptide in diagnosing "syndrome X," which is characterized by insulin resistance. Weak positive correlations between twenty-four-hour urine C-peptide concentration and body mass index, systolic blood pressure (BP), diastolic BP, serum total cholesterol, and serum triglyceride were detected. A weak negative correlation was also apparent between urine C-peptide and serum high-density lipoprotein (HDL). The body mass index and serum triglyceride of patients with urine C-peptide excretion of > 100 micrograms/day were significantly higher than those in patients with normal urine C-peptide excretion (< 100 micrograms/day) (P < 0.01 and P < 0.02, respectively). Systolic BP, diastolic BP, serum total cholesterol, and serum HDL did not differ significantly between the two groups of patients. Results indicate that twenty-four-hour urine C-peptide concentration is of significance in determining whether a patient has a tendency to insulin resistance but has only limited value as a quantitative measure of endogenous insulin secretion.

Feasibility and efficacy of intensive insulin therapy in type 1 diabetes mellitus in primary care

To determine the feasibility and efficacy of structured education in intensive insulin therapy (IIT) in patients with Type 1 diabetes mellitus commonly attended by primary care physicians, a prospective case-control study was carried out in co-operation with 26 general practitioners in rural Alpine region and the diabetes service at the University of Vienna, Medical School, Austria. From 89 rural Type 1 diabetic patients on conventional insulin therapy (CIT), those volunteering for better diabetes care (n = 52) were trained in IIT in the diabetes education centre and subsequently received their outpatient service by their general practitioners, as did those remaining on CIT (n = 37). Patients were matched as case-controls (n = 36 in each therapy group) for metabolic control at baseline (IIT/CIT: HbA1c 8.2 +/- 1.8 vs 8.1 +/- 2.0%, ns), age, duration of diabetes, incidence of retinopathy and nephropathy. Analysing an observation period of > 4.5 years, patients trained in IIT presented with improved metabolic control as compared to those on CIT (Mean HbA1c: IIT, 6.9 +/- 1.0%; CIT, 7.9 +/- 1.3%, p < 0.05, ANOVA). No difference between groups was, however, observed at the end-point of the study in HbA1c (IIT, 7.3 +/- 1.3%; CIT, 7.8 +/- 1.4%; IIT vs CIT, p = 0.14) and in the development of diabetic microangiopathy, frequency of reported severe hypoglycaemic episodes, and increase in body weight.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin regimens for the non-insulin dependent: impact on diurnal metabolic state and quality of life

A randomized prospective study was conducted to determine whether the insulin regimen for NIDDM subjects poorly controlled on oral therapy should be designed primarily to control basal metabolism or to control mealtime hyperglycaemia. Grossly obese subjects were excluded. After a 2-month run-in phase involving intensive education, subjects were randomized to therapy with twice daily isophane or three times daily soluble insulin. Both Protaphane and Actrapid brought about similar improvement in HbA1 (9.5 +/- 0.5 and 9.7 +/- 0.4%) compared with baseline (11.7 +/- 0.5%; p < 0.001). Diurnal blood glucose profiles showed that despite the good post-prandial control achieved by pre-meal soluble insulin, loss of control occurred overnight, resulting in higher fasting blood glucose levels compared with Protaphane therapy (8.0 +/- 0.8 vs 10.6 +/- 0.8 mmol l-1; p < 0.05). The overall rate of hypoglycaemia was 0.44 patient-1 year-1. Thirty-two mild hypoglycaemic episodes occurred on Protaphane therapy and 79 on Actrapid therapy. Using formal psychometric tests it was shown that insulin therapy was associated with improved treatment satisfaction and that this was greater on Protaphane therapy (p < 0.05). Overall well-being increased similarly in the two groups. All subjects wished to continue with insulin therapy after the conclusion of the study. The insulin regimen for moderately or poorly controlled non-insulin-dependent diabetes should primarily be designed to correct the basal insulin deficiency rather than to mimic normal meal-induced insulin secretion.

Insulin production following intravenous glucose, arginine, and valine: different pattern in patients with impaired glucose tolerance and non-insulin-dependent diabetes mellitus

To better understand abnormal insulin production (IP) in states of carbohydrate intolerance, insulin release was quantified following equimolar (2.4 mmol/kg) infusions of glucose, arginine, and valine in healthy subjects ([HS] age, 45 +/- 3 years; body mass index [BMI, kg/m2], 26.3 +/- 2.4; means +/- SEM), obese subjects with impaired glucose tolerance ([IGT] age, 43 +/- 5 years; BMI, 35.4 +/- 2.4), and non-obese patients with chronic non-insulin-dependent diabetes mellitus ([NIDDM] age, 55 +/- 3 years; BMI, 26.4 +/- 1.4; duration of disease, 13 +/- 3 years). There were eight subjects per group. Incremental IP (metabolic clearance rate of C-peptide [MCRCP] x total incremental area under the curve of plasma C-peptide [AUCCP], pmol/kg) following substrate infusion was as follows: glucose: HS, 227 +/- 14; IGT, 1,050 +/- 184 (P < .001 v HS); NIDDM, 114 +/- 27 (P < .001 v HS); arginine: HS, 139 +/- 23; IGT, 488 +/- 106 (P < .01 v HS); NIDDM, 206 +/- 47; and valine: HS, 21 +/- 7; IGT, 32 +/- 10; NIDDM, 54 +/- 12 (P < .01 v HS). The fractional clearance rate ([FCR] k, %/min) was impaired in IGT and NIDDM for glucose (HS, 3.9 +/- 0.4; IGT, 2.3 +/- 0.3 [P < .01 v HS]; NIDDM, 1.4 +/- 0.1 [P < .001 v HS]), arginine (2.4 +/- 0.1; 1.9 +/- 0.2 [P < .01 v HS]; 1.9 +/- 0.2 [P < .01 v HS]), and valine (0.95 +/- 0.06; 0.65 +/- 0.09 [P < .05 v HS]; 0.74 +/- 0.1 [P < .05 v HS]).(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Beta-cell hypersecretion and not reduced hepatic insulin extraction is the main cause of hyperinsulinemia in obese nondiabetic subjects

Obesity is characterized by peripheral hyperinsulinemia, for which either beta-cell hypersecretion, diminished hepatic insulin extraction, or both may be responsible. To clarify this issue, we investigated insulin secretion and hormone hepatic extraction in 18 nondiabetic obese patients (body mass index [BMI], 39 +/- 1.3 kg/m2) and 18 healthy, lean control subjects (BMI, 21.3 +/- 0.7 kg/m2). Body fat distribution was calculated by measuring the waist to hip ratio (WHR). A highly reduced tissue insulin sensitivity (2.4 +/- 0.5 v 9.5 +/- 1.5 10(4).min-1/[microU/mL], P > .0005) and glucose effectiveness, ie, glucose's ability to stimulate its own disappearance at basal insulin (16 +/- 2 v 30 +/- 3 10(3).min-1, P > .005), were found in the overweight subjects compared with the controls. The basal (76 +/- 14 v 37 +/- 4 pmol/L/min) and total (377,848 +/- 5,562 v 16,864 +/- 1,850 pmol/L) prehepatic insulin secretion and the basal (15 +/- 2 v 7 +/- 0.7 pmol/L/min) and total (8,286 +/- 2,009 v 2,840 +/- 210 pmol/L) posthepatic insulin delivery were significantly higher in the overweight subjects compared with the controls (P < .005), whereas the mean hepatic insulin extraction did not differ (77.8% +/- 2.6% v 79.5% +/- 2.6%). A significant inverse correlation was found between the hepatic insulin extraction and the WHR (r = .5, P > .04), signifying the importance of fat distribution in insulin metabolism. The obese patients were subdivided into two subgroups according to their glucose tolerance; eight patients exhibited a normal tolerance and the remaining 10 were intolerant.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional effects and clearance of endothelin-1 across pulmonary and splanchnic circulation

To determine the impact of i.v. endothelin-1 on systemic, pulmonary and splanchnic circulation, as well as the peptide's regional clearance, hepatic venous and right heart catheterization was performed in healthy volunteers. During the peptide's continuous i.v. administration (0.4 pmol x kg-1 x min-1, 60 min) its plasma concentration rose from 2.1 +/- 0.5 to 9.5 +/- 5.3 pmol/l (pulmonary artery), from 2.1 +/- 0.9 to 5.0 +/- 1.6 pmol/l (femoral artery), and from 1.5 +/- 0.6 to 2.9 +/- 1.2 pmol/l (hepatic vein). This was accompanied by an increase in mean systolic arterial pressure from 127 +/- 14 to 131 +/- 12 mmHg (P less than 0.05). Concomitantly, cardiac output and heart rate decreased from 7.0 +/- 1.1 to 5.8 +/- 1.0 l/min and from 63 +/- 6 to 56 +/- 5 beats/min, respectively, while total vascular resistance increased from 964 +/- 273 to 1204 +/- 338 dyn x cm x s-5 (P less than 0.01). No major changes in pulmonary circulation were observed, while splanchnic vascular resistance increased from 4472 +/- 1056 to 5361 +/- 1420 dyn x cm x s-5 (P less than 0.01) and estimated hepatic blood flow decreased from 1403 +/- 218 to 1218 +/- 219 ml min-1 (P less than 0.01). During endothelin-1 infusion the pulmonary vascular bed accounted for approximately 53% of the peptide's overall disposal.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood glucose response to stress hormone exposure in healthy man and insulin dependent diabetic patients: prediction by computer modeling

To establish a qualitative and quantitative model of blood glucose response to stress hormone exposure, healthy subjects (HS) on and off somatostatin (250 micrograms/h) as well as insulin dependent diabetic patients were infused with either epinephrine (E), glucagon (G), cortisol (F), growth hormone (GH) or with a cocktail of these hormones raising plasma stress hormones to values seen in severe diabetic ketoacidosis. The developed input/output model consists of two submodels interconnected in series plus two additional submodels for correction of gains describing both sensitivity of tissue response and utilisation as well as provision of glucose. It was shown and confirmed experimentally that blood glucose response to stress hormones was essentially nonlinear. Furthermore, the mathematical models for healthy subjects and for insulin dependent diabetic patients proved to be of the same structure and differed only in the values of some typical parameters. The model raises the possibility to describe and in part to predict blood glucose response to stress hormone exposure in healthy man and insulin dependent diabetic patients.

Fatty acids in the portal vein of the rat regulate hepatic insulin clearance

The effects of FFA on hepatic insulin clearance were studied in the in situ perfused rat liver. Clearance decreased with increasing body weight (age) of the rats. When FFA were added to the perfusate a 40% reduction of hepatic removal of insulin was found over the normal, physiological range (less than 1,000 mumol/liter), less pronounced in heavier rats. When perfusion was started with high concentrations of FFA, inhibition was rapidly reversible, a phenomenon again blunted in heavier rats. In contrast to FFA, different glucose concentrations in the perfusate did not affect the hepatic insulin uptake in the presence of FFA within physiological concentrations. Thus, hepatic clearance of insulin is proportional to rat weight (age) and portal FFA concentrations. Other studies have recently shown that fatty acids inhibit insulin binding, degradation, and function in isolated rat hepatocytes, and that hepatic clearance is inversely dependent on hepatic triglyceride concentrations, both inhibitions reversible by prevention of fatty acid oxidation. It is suggested that the diminished hepatic clearance of insulin in heavier (older) rats is at least partly due to their relative obesity and increased hepatic triglyceride contents. This effect as well as that of portal FFA is probably mediated via fatty acid oxidation in the liver. This mechanism may have implications for the regulation of hepatic metabolism, and peripheral insulin concentrations.

Effect of stress hormones on transsplanchnic balance of exogenous amino acid in healthy man

The effect of stress hormones on transsplanchnic balance of basal and infused amino acids (AA: Val,Met,Ile,Leu,Phe,Lys,His) was investigated in healthy men without and with added epinephrine (EPI) and dexamethasone (DEX). Concentrations of AA and blood glucose were measured in arterial and hepatic venous blood before and after primed-continuous (t = 120 minutes) AA infusion without (group I: controls; n = 6, 24 +/- 3 years), and with intravenous (IV) EPI infusion (group II: 6 micrograms/min, t = -75 to 120 minutes; n = 6, 26 +/- 5 years) or oral DEX pretreatment (group III: 6 mg/d for 2 days; n = 7, 26 +/- 3 years). In the absence of exogenous AA, EPI was demonstrated to increase estimated hepatic plasma flow (EHPF, mL/min: 1,019 +/- 133 [mean +/- SD] v 737 +/- 153; P less than .01), splanchnic output of glucose (SGO), and splanchnic uptake of total AA (nmol/kg.min: 4,657 +/- 2,014 v 2,802 +/- 704; P less than .05), of Gln (+78%) and of Gly (+100%). DEX did not affect EHPF or SGO, but doubled basal splanchnic AA uptake (5,446 +/- 3,635 nmol/kg.min) and increased that of Gln by 110%. Following AA administration, total splanchnic AA uptake was consistently increased (group I, 8,577 +/- 2,380; II, 8,957 +/- 3,714; III, 10,757 +/- 2,689 nmol/kg.min) as was splanchnic Gln uptake, both of which did not differ versus controls following EPI or DEX exposure. However, metabolic clearance rate (MCR, L/min) of infused AA was elevated by 40% (Met) to 85% (Leu) versus controls in subjects receiving EPI, but unchanged in those receiving oral DEX.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition by etomoxir of carnitine palmitoyltransferase I reduces hepatic glucose production and plasma lipids in non-insulin-dependent diabetes mellitus

To determine the therapeutic effect of the carinitine palmitoyltransferase I (CPT-I) inhibitor, etomoxir, eight hospitalized obese non-insulin-dependent diabetes mellitus (NIDDM) patients were studied (body mass index [BMI], 28.7 +/- 1.3 kg/m2; age, 54 +/- 8 years [means +/- SE]) at baseline (placebo = t1), and after oral etomoxir (50 mg/d = t2, 100 mg = 3, 150 mg = t4, 200 mg = t5, placebo = t6). Fasting blood glucose (mmol/L), triglycerides (mmol/L), cholesterol (mmol/L), free fatty acids (mumol/L), beta-hydroxybutyrate (mumol/L), and alanine aminotransferase (GPT, U/L) were determined (t1 to t6), as were glucose utilization (M value; indirect calorimetry) and hepatic glucose production during a 10 mU/kg.min euglycemic clamp (t1 and t4). A dose-dependent decrease was induced by etomoxir in fasting blood glucose (t1 to t5: 9.5 +/- 0.7, 8.7 +/- 1.0, 8.3 +/- 1.1 [P v t1 less than .05], 7.8 +/- 0.9, [P v t1 less than .01], 7.9 +/- 1.1 [P v t1 less than .05]), which was reversible in t6 (9.9 +/- 1.1). Mean plasma lipids were reduced (t1 v t5) for triglycerides (-54%, P v t1 less than .01), cholesterol (-24%, P v t1 less than .05), and beta-hydroxybutyrate (-44%, P v t2 less than .01), while free fatty acids increased by 52% (P v t1 less than .05), as did GPT (t1: 17 +/- 3; t5: 32 +/- 7 U/L [P v t1 less than .01]).(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased postheparin lipolytic activity in renal transplant recipients with cyclosporin A

The patterns of hyperlipidemia in renal transplant recipients (RTRs) are more variable than in the uremic state, showing increases in both very low-density lipoprotein (VLDL) and low density lipoprotein (LDL). This has been attributed, at least in part, to immunosuppressive therapy, especially to treatment with corticosteroids. Postheparin lipolytic activity (PHLA) was determined in 28 RTRs. Sixteen patients presenting with hyperlipidemia comprised group A, who were aged 49.8 +/- 13.5 years, and had a cholesterol of 8.24 +/- 1.86 mmol/liter, triglycerides of 6.02 +/- 3.33 mmol/liter. Twelve patients presenting cholesterol and triglyceride values within the normal range were in group B, and were aged 48.6 +/- 13.3 years. All RTRs received cyclosporin A (CsA) twice daily orally, which were divided in two equal doses and adjusted to provide CsA blood trough levels (RIA) in a range of 250 to 350 ng/ml. Twenty-one RTRs were additionally treated by alternate-day corticosteroids, whereas seven patients had CsA on their sole immunosuppressive agent. PHLA (mumol free fatty acids/ml/hr, given 10 and 20 min after 100 U/heparin kg body wt intravenously) was commonly reduced in RTRs (group A at 10/20 min: 5.6 +/- 1.1/5.26 +/- 1.2; group B: 8.26 +/- 2.91/8.38 +/- 3.44) as compared to the values obtained in healthy controls (15.3 +/- 2.9/17.2 +/- 5.0). This was mainly due to a reduction of the activity of the hepatic triglyceride lipase, and to a minor extent to a reduced activity of peripheral lipoprotein lipase. There was no statistically significant difference of PHLA in RTRs with or without corticosteroid treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of effect of tenoxicam on dynamic responses to concurrent oral doses of glucose and glibenclamide

1. In a single-blind, placebo controlled study the influence of tenoxicam on responses of glucose, insulin and C-peptide to oral doses of glucose and glibenclamide was examined in 16 healthy male volunteers. 2. The subjects received once daily doses of 2.5 mg glibenclamide for 12 days. From day 5 through 12 eight subjects received concomitantly 20 mg tenoxicam once daily and the remaining eight subjects received placebo. 3. On days 1, 4, 5 and 12 glibenclamide was taken with 75 g glucose and blood glucose, serum insulin and C-peptide were measured over 5 h. Plasma levels of glibenclamide and tenoxicam (where appropriate) were followed over 10 h. 4. Characteristic parameters of blood glucose and insulin and C-peptide responses did not change significantly with time (day) and there was no difference between both treatment groups. 5. Baseline insulin increased from 11.7 mu l-1 on day 1 to 15.6 mu l-1 on day 4 (P = 0.009), likewise baseline C-peptide increased from 478 pmol l-1 to 530 pmol l-1 (P = 0.05), but there was no further change in the subsequent treatment period. 6. The AUC of the glibenclamide plasma concentration-time curve did not show changes with time or differences between treatment groups. The mean (s.d.) oral clearance of tenoxicam was 2.5 (1.5) ml min-1 and appeared slightly higher than in previous studies. 7. It was concluded that tenoxicam did not affect overall glycoregulation in healthy subjects under glibenclamide steady state conditions.

Quantitative and qualitative differences in basal and glucose- and arginine-stimulated insulin secretion in healthy subjects and different stages of NIDDM

To determine quantitative and qualitative differences in insulin secretion equimolar amounts of glucose and arginine were infused in 9 healthy subjects, in 8 individuals each with obesity without and with impaired glucose tolerance, and in non-obese and obese non-insulin-dependent diabetic patients (NIDDM). Insulin secretion was calculated after individual determination of metabolic clearance rate of C-peptide (MCRcp) both as the area under the C-peptide concentration curve times MCRcp, and by a mono-compartment mathematical model, both yielding identical results. MCRcp fell consistently with increasing C-peptide infusion rate (e.g.: healthy subjects: C-peptide, 10 nmol/h, 4.2 +/- 0.4; 20 nmol/h, 3.3 +/- 0.3; 30 nmol/h, 3.1 +/- 0.2 ml/kg.min; p less than 0.05 to p less than 0.01). Basal insulin secretion was 2.1-fold greater in the obese with impaired glucose tolerance than in healthy subjects, but was unchanged in non-obese NIDDM. Glucose and arginine triggered insulin release was greater than in healthy subjects at almost identical area under the respective substrate concentration curve (AUC/kg body weight) in obese subjects without (2-fold) and with impaired glucose tolerance (4-fold), and in NIDDMs following i.v. arginine (2-fold). The mean ratio of incremental insulin release to i.v. glucose and arginine was smaller in NIDDM (normal weight, 1.3 +/- 0.4; obese, 1.0 +/- 0.2) than in healthy (2.0 +/- 0.3), or obese subjects with impaired glucose tolerance (2.8 +/- 0.7). Stimulated C-peptide/insulin ratio was reduced in all patients vs that in healthy subjects (p less than 0.05). We conclude that (a) MCR of C-peptide is in part a saturable process; (b) insulin clearance may be impaired in obesity and NIDDM; and (c) insulin secretion differs in obese states and NIDDM both quantitatively and qualitatively, and thereby separates the two disorders as different entities. In addition, quantitation of insulin release in obese states may also help (d) to better define primary algorithms for insulin replacement in normal- and overweight insulin-dependent diabetic patients.

Effects of four orally administered analogues of prostaglandin E1 and E2 on glucose tolerance and on the secretion of pancreatic and gastrointestinal hormones in man

Oral glucose tolerance tests (75 g, 300 ml) were performed in 12 healthy volunteers, with prior administration of placebo, misoprostol (400 micrograms), rioprostil (300 micrograms), enprostil (70 micrograms), or nocloprost (200 micrograms), in a double-blind, randomized manner. None of the drugs significantly affected glucose tolerance, although with misoprostal some volunteers displayed an impaired glucose tolerance. Nocloprost was without effect on gastric inhibitory polypeptide (GIP) and did not influence insulin or C-peptide concentrations. Misoprostol and rioprostil reduced integrated incremental responses of GIP by 57% (P less than or equal to 0.001) and 45% (P less than or equal to 0.01), respectively, and both gave rise to an initial (approximately 10 min) delay of insulin and C-peptide responses, without a significant overall reduction in integrated incremental responses. Enprostil almost totally inhibited the GIP response (by 94%; P less than or equal to 0.001), delayed initial insulin and C-peptide responses, but reduced the integrated incremental C-peptide response (which corresponds to the overall release of insulin) by only 14% (P less than or equal to 0.05). Enprostil more substantially reduced the integrated incremental response of insulin by 36% (P less than or equal to 0.01), and also reduced the ratio of insulin and C-peptide incremental responses (P less than or equal to 0.001). In conclusion, prostaglandin E analogues which caused a reduction in GIP responses, and thereby disrupting the enteroinsular axis to varying degrees, delayed the time-course of insulin secretion without a significant impact on glucose tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of ACE inhibition with cilazapril on splanchnic and systemic haemodynamics in man

1. There is recent experimental evidence that the renin-angiotensin-system may play an essential role in producing splanchnic vasoconstriction. However, controversy exists as to the influence of ACE inhibition on splanchnic haemodynamics in man. We therefore investigated whether cilazapril, a structurally new and long-acting ACE inhibitor, interacts with angiotensin I-dependent changes in splanchnic haemodynamics in man, using an experimental model. 2. The effects of cilazapril on angiotensin I-induced splanchnic and systemic haemodynamics were studied in seven normotensive men using the hepatic venous catheter technique (indocyanine-green dye), right-heart catheterisation (thermodilution method), intra-arterial blood pressure monitoring and systolic time-intervals. Dose-responses to angiotensin I were determined under control conditions and 60 min after ACE inhibition with 5 mg oral cilazapril. Angiotensin I was infused intravenously at constant rates in an increasing dose-sequence until systolic blood pressure was greater than 30 mm Hg. 3. ACE inhibition with cilazapril did not change basal splanchnic or systemic haemodynamics to any relevant extent. The angiotensin I dependent increase in systemic and pulmonary resistance and pulmonary capillary wedge pressure was attenuated by cilazapril, as indicated by the shift of the dose-response curves to the right. In the splanchnic vascular bed angiotensin I dose-dependently increased splanchnic vascular resistance and also wedge hepatic venous pressure and decreased splanchnic blood flow. These angiotensin I induced haemodynamic changes were clearly suppressed by cilazapril. The angiotensin I dose needed to produce a 30% increase in splanchnic vascular resistance, given as mean and s.e. mean, was 1.7 +/- 0.3 micrograms min-1 during control-trials vs 7.3 +/- 1.3 micrograms min-1 after ACE inhibition with cilazapril (P less than 0.001). 4. We conclude that, in man, the influence of cilazapril on acute angiotensin I-mediated haemodynamic responses is present in the splanchnic vascular bed, and that the overall effects of cilazapril are consistent with both arterial and venous effects of the ACE inhibitor. Cilazapril effectively counteracts angiotensin I-induced splanchnic vasoconstriction.

Insulin resistance in Graves' disease: a quantitative in-vivo evaluation

Hyperthyroidism is considered to be an insulin-resistant state, but a quantitative evaluation of some action of insulin is still lacking. We performed euglycaemic clamp at about 350 and 7000 pmol l-1 plasma insulin concentration in combination with the 3H-glucose infusion in 12 patients with Graves' disease and in 12 matched controls. Fasting plasma insulin (126 +/- 6.5 vs. 77.5 +/- 5.7 pmol l-1; P less than 0.001), C-peptide (502 +/- 36 vs. 363 +/- 41 pmol l-1; P less than 0.001) and glucagon (47 +/- 3.3 vs. 33.3 +/- 3 pmol l-1; P less than 0.01) were significantly higher in hyperthyroids than in euthyroids. Basal hepatic glucose production was significantly higher in hyperthyroids than in euthyroids (18.3 +/- 1.4 vs. 9.2 +/- 0.5 mumol l-1; P less than 0.0001), and its suppression during physiological hyperinsulinaemia was only 50% in hyperthyroids. Glucose utilization and suppression of lipolysis were normally stimulated by insulin. All parameters altered during hyperthyroidism were normalized during methimazole-induced euthyroidism. We conclude that insulin resistance involves mainly glucose rather than lipid and is selective at the hepatic level.

First-phase insulin response to glucose in nonobese or obese subjects with glucose intolerance: analysis by C-peptide secretion rate

This study was proposed to clarify the impairment of first-phase insulin response to glucose in subjects with glucose intolerance by analysis of C-peptide secretion rate after glucose or glucagon injection. The rate was calculated from kinetic analysis of peripheral C-peptide behavior. The rate reached the peak two minutes after glucose injection and then rapidly declined (first-phase secretion) in control subjects. In nonobese subjects with impaired glucose tolerance (IGT) or non-insulin-dependent diabetes mellitus (NIDDM), the rate promptly increased in response to glucose and was followed by a second phase increase. The time course of the rate in the subjects was slightly different from that in control subjects. There was a progressively greater deficit in the first-phase increase with increasing severity of glucose intolerance. The time course of the rate in the obese subjects with NIDDM was different from that in control subjects. The first-phase increase was reduced in the obese subjects with NIDDM. The glucose disappearance rate was correlated with the first-phase increase. Since the time course of the rate after glucagon injection in all subjects did correspond well with that in the control subjects, variation of metabolic clearance rate of endogenous C-peptide among the subjects may be negligible for this study. This study provides the precise time course of first- and second-phase insulin response to glucose injection in nonobese and obese subjects with IGT or NIDDM as well as convincing evidence of the progressive reduction of first-phase insulin response with increasing severity of glucose intolerance. First-phase insulin response to glucose might be slightly delayed in some obese subjects with NIDDM.