Failure of glucagon suppression contributes to postprandial hyperglycaemia in IDDM

Summary Carbohydrate ingestion results in a fall in glucagon concentration in non-diabetic but not in diabetic individuals. To determine if, and the mechanism by which, lack of postprandial suppression of glucagon contributes to hyperglycaemia, nine subjects with insulin-dependent diabetes mellitus (IDDM) ingested 50 g of glucose containing both [2-³H] glucose and [6-³H] glucose on two occasions. [6-¹⁴C] glucose, insulin and low-dose somatostatin were infused intravenously at the same rates on both occasions. A basal glucagon infusion was started either at the same time (constant glucagon) or 2 h following (suppressed glucagon) glucose ingestion. This resulted in lower (p<0.001) glucagon concentrations during the first 2 h of the suppressed than during the constant glucagon study days (63±1 vs 108±2 pg/ ml). Lack of suppression of glucagon led to higher (p<0.01) postprandial glucose concentrations (10.3±0.9 vs 8.1±0.7 mmol/l) and a greater (p<0.02) integrated glycaemic response. The excessive rise in glucose was due to higher (p<0.02) rates of postprandial hepatic glucose release during the constant than during the suppressed glucagon study days, whether measured using either [6-³H] glucose (2.6±0.2 vs 2.0±0.2 mmol·kg^–1 per 6 h) or [2-³H] glucose (3.0±0.3 vs 2.4±0.2 mmol·kg^–1 per 6 h) as the meal tracer. Glucose disappearance, initial splanchnic glucose clearance and hepatic glucose cycling did not differ on the two occasions. Thus, the present studies demonstrate that lack of postprandial suppression of glucagon, by increasing hepatic glucose release, contributes to hyperglycaemia in subjects with IDDM.Abbreviations IDDM Insulin-dependent diabetes mellitus     

Lack of preservation of higher brain function during hypoglycaemia in patients with intensively-treated IDDM

Summary Severe hypoglycaemia with cognitive dysfunction is 3 times more common in intensively, rather than conventionally, treated insulin-dependent diabetes mellitus (IDDM). To investigate the effect of diabetes control on higher brain function during acute hypoglycaemia, we studied one of the earliest detectable changes in cognitive function, i.e. the four-choice reaction time, and symptomatic and hormonal responses during euglycaemic and hypoglycaemic clamping in human subjects. There were no changes in symptoms or counterregulatory hormones and four-choice reaction time was stable during 220 min of euglycaemic insulin clamping in five men with IDDM, with a coefficient of variation of less than 2.2% (1% for accuracy) for the cognitive function test. During stepped hypoglycaemic clamping however, hormonal responses and subjective awareness of hypoglycaemia occurred in all groups but started at much lower blood glucose concentrations in eight intensively-treated diabetic subjects (Group 1) than in ten conventionally-treated (Group 2) or in eight non-diabetic subjects (Group 3). For example, for adrenaline, plasma glucose thresholds were 2.7±0.2 vs 3.4±0.2 and 3.2±0.1 mmol/l, respectively, p<0.05, Group 1 vs Groups 2 or 3 and for subjective awareness of hypoglycaemia 2.3±0.2 vs 3.0±0.1 and 3.2±0.1 mmol/l, p 0.003), as in previous studies. In contrast, deterioration in reaction time occurred at 3.2±0.3, 3.2±0.2 and 3.0+0.2 mmol/l, respectively (p=NS), thus occurring at higher glucose levels than subjective awareness in the intensively-treated subjects only. The altered hierarchy of responses to hypoglycaemia in well-controlled intensively-treated diabetes explains the increased risk of severe hypoglycaemia without warning seen in such patients.Abbreviations IDDM Insulin-dependent diabetes mellitus     

Influence of glucagon on plasma levels of potassium in man

Summary To investigate the role played by glucagon in the regulation of plasma potassium, we have examined the behaviour of this ion during four 2 h infusions of saline, glucagon (200 ng/min), cyclic somatostatin (priming dose of 50 g followed by 5.8 g/min) and somatostatin plus glucagon in 6 normal volunteers. Glucagon alone produced no change in potassium, despite an increase in insulin. Somatostatin, in addition to depressing insulin, produced a slight but significant (p < 0.01) increase in potassium ( max: 0.2–0.8 mmol/l: mean ± SEM, 0.4±0.1). Infusion of somatostatin together with glucagon suppressed the glucagon-induced increase in insulin and greatly augmented the increase in blood glucose. Potassium rose significantly more (p < 0.02) than after somatostatin alone ( max: 0.5–1.3 mmol/l; mean 0.9±0.1), indicating that hyperkalaemia results from hyperglucagonaemia in the absence of insulin. Evidence is presented that this last phenomenon is not mediated by hyperglycaemia or by a reduction in aldosterone secretion. It is suggested that low blood insulin and increased glucagon could be one of the mechanisms that underlie or magnify the hyperkalaemia observed in cases of serious stress or decompensated diabetes.     

Increased hepatic secretion of very-low-density lipoprotein apolipoprotein B-100 in NIDDM

Summary We measured the hepatic secretion of very-low-density lipoprotein apolipoprotein B-100 (VLDL apoB) using a stable isotope gas-chromatography mass-spectrometry method in six patients with non-insulin-dependent diabetes mellitus (NIDDM) (four males, two females, age 57.5±2.2 years (mean±SEM), weight 88.2±5.5 kg, glycated haemoglobin (HbA₁) 8.5±0.5%, plasma total cholesterol concentration 5.7±0.5 mmol/l, triglyceride 3.8±0.9 mmol/l, high-density lipoprotein (HDL) cholesterol 1.0±0.1 mmol/l) and six non-diabetic subjects matched for age, sex and weight (four males, two females, age 55.7±2.8 years, weight 85.8±5.6 kg, HbA₁ 6.5±0.1%, plasma total cholesterol concentration 5.7±0.5 mmol/l, triglyceride 1.2±0.1 mmol/l, HDL cholesterol 1.4±0.1 mmol/l). HbA₁, plasma triglyceride and mevalpnic acid (an index of cholesterol synthesis in vivo) concentrations were significantly higher in the diabetic patients than in the non-diabetic subjects (p=0.006, p=0.02 and p=0.004, respectively). VLDL apoB absolute secretion rate was significantly higher in the diabetic patients compared with the non-diabetic subjects (2297±491 vs 921±115 mg/day, p<0.05), but there was no significant difference in the fractional catabolic rate of VLDL apoB. There was a positive correlation between VLDL apoB secretion rate and (i) fasting C-peptide (r=0.84, p=0.04) and (ii) mevalonic acid concentration (r=0.83, p<0.05) in the diabetic patients but not in the non-diabetic subjects. There was also a significant positive association between plasma mevalonic acid and plasma C-peptide (r=0.82, p<0.05) concentrations in the diabetic patients. We conclude that in NIDDM, there is increased hepatic secretion of VLDL apoB which may partly explain the dyslipoproteinaemia seen in this condition. We suggest that increased secretion of this apolipoprotein may be a consequence of resistance to the inhibitory effect of insulin on VLDL apoB secretion. Insulin resistance may also be the mechanism by which cholesterol synthesis, a regulator of apoB secretion, is increased in NIDDM.Abbreviations ApoB Apolipoprotein B-100 - VLDL very-low-density lipoprotein - GCMS gas-chromatography mass-spectrometry - MVA mevalonic acid - Hep G2 hepatoma G2 - -KIC -ketoisocaproic acid - TC total cholesterol - TG triglyceride - NEFA non-esterified fatty acids - FSR fractional secretion rate - ASR absolute secretion rate - m/z mass to charge ratio - CV coefficient of variation     

The metabolic response to hyperglycaemic clamping in insulin-dependent diabetes

Summary The metabolic and hormonal effects of stable hyperglycaemia (10–12 mmol/l) have been examined in five insulin-dependent diabetics and compared with the results of 8 h (1200 to 2000 h) normoglycaemic (5–6 mmol/l) clamping. Glucose levels were maintained using a glucose controlled insulin infusion system. Mean blood lactate, pyruvate, total ketone bodies, glycerol and plasma nonesterified fatty acids were similar during the period of stable glycaemia at the two glucose levels. In contrast mean blood alanine was markedly elevated during hyperglycaemic clamping (0.384 ± 0.008 vs 0.298 ± 0.021 mmol/l) and 3-hydroxybutyrate was slightly decreased (0.068 ± 0.007 vs 0.084 ± 0.008 mmol/l). Plasma glucagon levels were raised during hyperglycaemic clamping and growth hormone slightly decreased. There was a close positive correlation between mean blood alanine and mean blood glucose (r = 0.79, p < 0.01), and a negative correlation of alanine with the amount of insulin infused (r =-0.72, p < 0.01). It is suggested that the raised alanine results from increased peripheral glucose utilisation. In general a short period of stable hyperglycaemia is not associated with a worsening of metabolic abnormalities in insulin-dependent diabetic subjects.     

Effect of hyperglycaemia on inflammatory and stress responses and clinical outcome of pneumonia in non-critical-care inpatients: results from an observational cohort study

Aims/hypothesis

Despite the condition’s high prevalence, the influence of hyperglycaemia on clinical outcomes in non-critical-care inpatients with infections remains ill defined. In this study, we analysed associations of glucose levels at admission and during initial inpatient treatment with the inflammatory response and clinical outcome in community-acquired pneumonia (CAP) patients.

Methods

This secondary observational analysis included 880 confirmed CAP patients. We used severity-adjusted multivariate regression models to investigate associations of initial and 96 h mean glucose levels with serially measured biomarker levels over 7 days (C-reactive protein [CRP], procalcitonin, white blood cell count [WBC], pro-adrenomedullin [ProADM]) and adverse clinical course (death and intensive-care unit admission).

Results

In the 724 non-diabetic patients (82.3% of the study population), moderate or severe hyperglycaemia (glucose 6–11 mmol/l and >11 mmol/l, respectively) was associated with increased risk for adverse clinical course (adjusted OR [95% CI] 1.4 [0.8, 2.4] and 3.0 [1.1, 8.0], respectively) and with higher CRP, WBC and ProADM levels over 7 days (p?<?0.05, ANOVA, all days). In diabetic patients (n?=?156), no similar associations were found for initial hyperglycaemia, although mean 96 h glucose levels ?≥?9 mmol/l were associated with adverse clinical course (adjusted OR 5.4 [1.1, 25.8]; p?=?0.03). No effect modification by insulin treatment was detected (interaction terms p?>?0.2 for all analyses).

Conclusions/interpretation

Initial hyperglycaemia in non-diabetic CAP patients, and prolonged hyperglycaemia in diabetic or non-diabetic CAP patients, are associated with a more pronounced inflammatory response and CAP-related adverse clinical outcome. Optimal glucose targets for insulin treatment of hyperglycaemia in non-critical-care settings should be defined.     

Protective effect of vitamin E supplementation on increased thermal stability of collagen in diabetic rats

Summary Products similar to non-enzymatic glycation end products are known to arise from the interactions between proteins and lipid peroxides in vitro. In this study, we assessed the effect of vitamin E, which possibly modifies lipid peroxide, on advanced glycation end products or similar products in vivo by measuring the fluorescence and thermal rupture time of tail tendon collagen in streptozotocin-induced diabetic rats. The diabetic rats and non-diabetic rats were fed a vitamin E supplemented diet, and a control diet starting 3 days after the streptozotocin injection. After the 4-week treatment, the serum lipid peroxide levels expressed as thiobarbituric acid reactants in the diabetic rats on control diet (15.9 ± 2.6 mol/l [SEM]) were significantly (p <0.05) higher than in the non-diabetic rats (7.9 ± 1.3 mol/l on control diet and 3.3 ± 0.4 mol/l on supplemented diet), but the levels in the diabetic rats on supplemented diet (7.9 + 2.3 mol/l) were reduced to the normal levels. No significant differences were found in serum glucose and glycated haemoglobin levels within the diabetic rats on control and supplemented diets. Both the fluorescence and thermal rupture time of collagen were significantly (p <0.05) increased in the diabetic rats on both diets compared with those in the corresponding non-diabetic rats. Although there was no significant difference in the collagen-linked fluorescence within the diabetic rats on control and supplemented diets, the thermal rupture time was significantly (p <0.01) shortened with supplemented diet (10.8 ± 0.7 min on supplemented diet vs 15.0 ± 0.7 min on control diet). The effect of vitamin E on the thermal rupture time was not observed in non-diabetic rats (6.6 ± 0.5 min on supplemented diet vs 6.2 ± 0.5 min on control diet). These results indicate that the formation of advanced glycation end products or similar products seen in hyperglycaemia can be partially inhibited by vitamin E supplementation by lowering lipid peroxide levels or oxidative stress. This study is thought to be the first to show vitamin E as an anti-oxidant agent limiting the formation of advanced glycation end products or similar products in vivo.     

Correlations between nerve function and tissue oxygenation in diabetic patients: further clues to the aetiology of diabetic neuropathy?

Summary Transcutaneous oxygen, laser Doppler flowmetry, peroneal nerve motor conduction velocity and skin temperature were assessed in both legs of 34 diabetic patients, who had a mean age of 41 (range 29–77) years, and diabetes duration of 21 (3–34) years. Transcutaneous oxygen significantly correlated with peroneal nerve motor conduction velocity (r=0.59 p<0.001) and laser Doppler flowmetry (r=0.7 p<0.001). Laser Doppler flowmetry correlated weakly with peroneal motor conduction velocity, (r=0.34 p<0.05). In each patient the leg with the higher transcutaneous oxygen (mean 70.2±9.3 (SD) mmHg) had a significantly higher peroneal motor conduction velocity (45.3±7.1 vs 41.5± 6.3 m/s, p<0.01), than the leg with the lower transcutaneous oxygen (61.0±11.9 mm Hg), though no difference in skin temperature was observed, 31.4±0.4 vs 31.1±0.5°C. We then assessed the potential for reversibility of conduction velocity deficits in ten non-diabetic patients, aged 59 (52–77) years, undergoing unilateral femoro-popliteal bypass, measuring transcutaneous oxygen, peroneal nerve motor conduction velocity and skin temperature pre- and 6 weeks post-surgery. In the control leg (unoperated) there was no significant change in transcutaneous oxygen (63.2±8.8 vs 63.0±4.6 mm Hg), peroneal nerve motor conduction velocity (45.1±7.8 vs 43.4±7.2 m/s) or skin temperature (30.8±1.3 vs 30.2±1.2°C) after surgery (all NS). In the operated leg, transcutaneous oxygen increased from 59.3±10.7 to 70.7±7.2 mm Hg (p<0.01), and peroneal nerve motor conduction velocity from 42.6±6.1 to 46.7±3.2 m/s (p<0.01), but skin temperature was unchanged 30.3±0.4 vs 30.4± 1.3°C (NS). These studies provide further evidence that peripheral nerve function is associated with tissue hypoxia and that improving tissue oxygenation can significantly improve nerve conduction over a short period of time.     

Chronic hyperglycaemia promotes lipogenesis and triacylglycerol accumulation in human skeletal muscle cells

Aims/hypothesis The present study was conducted to evaluate the effect of hyperglycaemia in itself on glucose and lipid metabolism in human skeletal muscle cells.Methods Satellite cells were isolated from biopsy samples from the vastus lateralis muscle and differentiated into multinucleated myotubes in cultures. Metabolism studies were performed using isotopes ([³H]deoxyglucose, [¹⁴C]glucose, [¹⁴C]oleic acid and [¹⁴C]palmitic acid), and mRNA and protein levels were analysed by real-time RT-PCR and western blotting respectively.Results Exposure of myotubes to 20 mmol/l glucose for 4 days reduced insulin-stimulated glucose uptake and glycogen synthesis to 57±5% (p<0.0001) and 56±5% (p<0.0001) of normoglycaemic (5.5 mmol/l glucose) controls respectively. Basal glucose uptake and glycogen synthesis were both reduced, whereas glucose oxidation was unaltered. Total cell content of glycogen and expression of GLUT1 and GLUT4 mRNA were not affected. There was a significant increase in the incorporation of glucose into cellular NEFA (88±17% increase, p=0.006), triacylglycerol (44±21% increase, p=0.04) and cholesterol ester (89±36% increase, p=0.02) in hyperglycaemic myotubes compared with controls. Diacylglycerol tended to be increased though not significantly, and phospholipid formation were unchanged. Relative to controls, total cell content of triacylglycerol was increased by 25±7% (p=0.02) and acyl-CoA:1,2-diacylglycerol acyltransferase 1 activity was increased by 34±4% (p=0.004), whereas acyl-CoA:1,2-diacylglycerol acyltransferase 1 mRNA expression was unchanged. Total cellular uptake of palmitic acid was reduced by 18±3% (p=0.006) in hyperglycaemic cells compared with controls, while uptake of oleic acid was unchanged. Oxidation of palmitic acid or oleic acid was not affected by hyperglycaemia.Conclusions/interpretation Chronic hyperglycaemia increased triacylglycerol accumulation and the incorporation of carbohydrate into triacylglycerol (i.e. de novo lipogenesis) concomitantly with a reduced insulin-stimulated glucose uptake and glycogen synthesis. Enhanced acyl-CoA:1,2-diacylglycerol acyltransferase 1 activity supported the increased triacylglycerol synthesis during hyperglycaemia.Abbreviations ASM acid-soluble metabolites - CE cholesterol ester - CPT-1 carnitine palmitoyltransferase 1 - DGAT-1 acyl-CoA:1,2-diacylglycerol acyltransferase 1 - MEM minimum essential medium medium - PKB protein kinase B - PKC protein kinase C - PL phospholipids - TAG triacylglycerol     

Post-hypoglycaemic hyperketonaemia does not contribute to brain metabolism during insulin-induced hypoglycaemia in humans

Summary It is controversial as to whether ketone bodies are utilized by the human brain as a fuel alternative to glucose during hypoglycaemia. To clarify the issue, we studied 10 normal volunteers during an experimental hypoglycaemia closely mimicking the clinical hypoglycaemia of patients with Type 1 (insulin-dependent) diabetes mellitus or insulinoma. Hypoglycaemia was induced by a continuous infusion of insulin (0.40 mU·kg^–1·min^–1 for 8 h, plasma insulin 180 pmol/l) which decreased the plasma glucose concentration to approximately 3.1 mmol/l during the last 3 h of the studies. Subjects were studied on two occasions, i. e. spontaneous, counterregulatory-induced post-hypoglycaemic increase in 3--hydroxybutyrate (from 0.2 to 1.1 mmol/l at 8 h), or prevention of post-hypoglycaemic hyperketonaemia (plasma -hydroxybutyrate 0.1 mmol/l throughout the study) after administration of acipimox, a potent inhibitor of lipolysis. In the latter study, glucose was infused to match the hypoglycaemia observed in the former study. The glycaemic thresholds and overall responses of counterregulatory hormones, symptoms (both autonomic and neuroglycopenic), and deterioration of cognitive function (psychomotor tests) were superimposable in the control study in which ketones increased spontaneously after onset of hypoglycaemic counterregulation, as compared to the study in which ketones were suppressed (p=NS). The fact that responses of counterregulatory hormones, symptoms and deterioration in cognitive function were not exaggerated when posthypoglycaemic hyperketonaemia was prevented, indicate that during hypoglycaemia, the counterregulatory-induced endogenous hyperketonaemia does not provide the human brain with an alternative substrate to glucose. Thus, it is concluded that during hypoglycaemia, endogenous hyperketonaemia does not contribute to brain metabolism and function.     

Glucose intolerance and impairment of insulin secretion in relation to vitamin D deficiency in East London Asians

Summary Vitamin D deficiency reduces insulin secretion and still occurs in East London Asians in whom the prevalence of diabetes mellitus is at least four times that of Caucasians. Vitamin D status was assessed in 44 of 65 non-diabetic subjects at risk of diabetes (spot blood glucose level >6.0 mmol/l <2 h post cibum, or >4.6 mmol/l >2 h post cibum on two separate occasions) and in 15 of 60 age and sex-matched low-risk control subjects who attended for oral glucose tolerance test (OGTT) after screening of 877 omnivorous subjects not known to have diabetes. It was found that 95% of at-risk and 80% of low-risk subjects were vitamin D deficient (serum 25-hydroxy-vitamin D <11 ng/ml). Diabetes was present in 16, impaired glucose tolerance in 12 and normoglycaemia in 19 at-risk subjects, impaired glucose tolerance in 2, and normoglycaemia in 13 low-risk subjects. Correlations of 30-min OGTT blood glucose, specific insulin and C-peptide levels with 25-hydroxy-vitamin D concentrations in 44 at-risk subjects were –0.31 (p=0.04), 0.59 (p=0.0001) and 0.44 (p=0.006). In 15 not-at-risk subjects 30-min OGTT specific insulin and C-peptide levels correlated with 25-hydroxy-vitamin D, r=0.39 (p=0.04) and 0.16 (p=0.43), respectively. Serum alkaline phosphatase concentration was higher in at-risk than not-at-risk subjects (59.6 vs 46.5 IU/l, p=0.012); corrected calcium concentrations were comparable (2.38 vs 2.39 mmol/l, p=0.7). Following treatment with 100,000 IU vitamin D by i.m. injection, specific insulin, C-peptide [30 min on OGTT] and 25-hydroxy-vitamin D concentrations had risen 8–12 weeks later [means±SD] from 57±62 to 96.2±82.4 mU/l [p=0.0017], 1.0±0.4 to 1.7±0.8 pmol/ml [p=0.0001] and 3.6±1.8 to 13.5±7.4 ng/ml [p=0.0001], (but not to low-risk group values of 179±89 mU/l, 2.7±1.14 pmol/ml and 8.16±6.4 ng/ml), respectively. Both total serum alkaline phosphatase and corrected calcium concentrations rose following vitamin D treatment in the at-risk subjects by 11.1±8.22 (from 44 to 55 IU/l) and 0.15±0.18, (2.43 to 2.57 mmol/l), respectively (p=0.004). Abnormal glucose tolerance was unchanged by vitamin D treatment. The value of early and sustained repletion with vitamin D in diabetes prophylaxis should be examined in communities where vitamin D depletion is common.Abbreviations OGTT Oral glucose tolerance test - IGT impaired glucose tolerance - p.c. post cibum - CV coefficient of variation - NEFA non-esterified fatty acids     

Effects of natural free radical scavengers on peripheral nerve and neurovascular function in diabetic rats

Summary Increased generation of reactive oxygen species, coupled with impaired endogenous scavenging mechanisms, plays a prominent role in the aetiology of neurovascular abnormalities in experimental diabetes mellitus. We examined the efficacy of the natural anti-oxidants vitamins C, E and -carotene in preventing nerve conduction and nutritive blood flow deficits in streptozotocin-diabetic rats. One month of diabetes caused a 19.1% reduction in sciatic motor conduction velocity (p<0.001). This was approximately prevented 80–90% by high-dose (1000 mg · kg^–1 · day^–1) vitamin E and -carotene treatments (p<0.001). Vitamin C had lesser effects; the maximum protection found for motor conduction velocity was 36% using a dose of 150 mg · kg^–1 · day^–1 (p<0.001). High dose (500 mg · kg^–1 · day^–1) vitamin C had a lesser effect on conduction than intermediate doses. Joint vitamin C and lower dose (500 mg · kg^–1 · day^–1) vitamin E treatment had a predominantly additive preventive effect against nerve dysfunction. Resistance to hypoxic conduction failure for sciatic nerve in vitro was markedly increased by diabetes and this remained relatively unaffected by treatment. Sciatic nutritive endoneurial blood flow, measured using microelectrode polarography and hydrogen clearance, was reduced 46.1% by 1 month of diabetes (p<0.001). This was prevented to the extent of 87%, 36% and 98% by vitamins E, C and -carotene, respectively (p<0.01). These data emphasize the role of oxidative stress in the development of early neurovascular changes in experimental diabetes and show that naturally available scavengers have a neuroprotective action.Abbreviations NCV Nerve conduction velocity - NO nitric oxide - ROS reactive oxygen species     

Increased glucose carbon recycling in severely insulin deficient Type 1 (insulin-dependent) diabetic subjects

Summary Six Type 1 (insulin-dependent) diabetic subjects were studied in order to determine the contribution of recycling of glucose carbon to the overproduction of glucose which is characteristic of the fasting hyperglycaemia produced by insulin withdrawal. The subjects were studied on two occasions, once after an overnight insulin infusion and once following 24 h of insulin withdrawal. The difference in turnover rates of 1-¹⁴C-glucose and 3-³H-glucose was used as a measure of glucose recycling. Insulin withdrawal caused a marked metabolic derangement with a rise in non-esterified fatty acids from 0.69±0.23 to 1.11±0.21 mmol/l (mean±SEM, p<0.05), total ketones from 0.27±0.06 to 2.06±0.51 mmol/l (p<0.01), cortisol from 341±43 to 479±31 nmol/l (p<0.05) and growth hormone from 1.1±0.3 to 19+5-mu/l (p<0.05). Glucose turnover rose from 13.8±2.3 mol·kg^–1·min^–1 at a glucose of 6.9±0.7 mmol/l in the insulin infused study to 25.8±4.4 mol·kg^–1·min^–1 (p<0.05) at a glucose of 16.4±0.7 mmol/l in the insulin withdrawn study. Recycling also rose from 3.0±0.4 mol· kg^–1·min^–1 to 9.4±2.2 mol·kg^–1·min^–1 (p<0.05) when insulin withdrawn, accounting for 23±3% and 36±3% of glucose turnover, respectively. We conclude that in the severely insulin deficient Type 1 diabetic subject recycling of glucose carbon is a major contributor to the excess glucose production.     

Previous exposure to glucose enhances somatostatin secretion from the isolated perfused rat pancreas

Summary Previous exposure to glucose enhances insulin and depresses glucagon secretion by the pancreas. We have investigated whether secretion of somatostatin is also influenced by a glucose priming effect. In perfused rat pancreas from 36 h fasted rats a 5 min pulse of arginine (8 mmol/l) rapidly elicited a peak of somatostatin release. A similar somatostatin response was evoked by a second, identical, pulse of arginine after perfusion with basal glucose (3.9 mmol/l) for 45 min. On the other hand when 27.7 mmol/l D-glucose, was administered for 20 min between arginine pulses, there was significant stimulation of somatostatin secretion. When arginine was re-introduced 15 min after the cessation of the pulse of elevated glucose the magnitude of the arginine-induced peak (min 0–2 of stimulation) was increased from 16.2±4.1 to 33.1±4.7 pg/2 min, p<0.01, relative to the first stimulation with arginine. None of these effects of glucose could be reproduced by Dgalactose. The somatostatin response to arginine was higher in pancreata from fed than from 36 h fasted animals as was also basal release (22.8±5.0 vs 9.0±2.0 pg/min). In the fed state the response to the second pulse of arginine was however reduced by 50% after perfusion with basal glucose. This decrease in responsiveness was counteracted by perfusion with 27.7 mmol/l glucose for 20 min between the arginine pulses. It is concluded that previous exposure to an elevated concentration of glucose enhances D-cell responsiveness to arginine in the fasted as well as the fed state.     

Insulin sensitivity,insulin secretion and glucose effectiveness in diabetic and non-diabetic cirrhotic patients

Summary In cirrhotic patients with normal fasting glucose levels both insulin insensitivity and a blunted early insulin response to oral glucose are important determinants of the degree of intolerance to oral glucose. It is not known whether the ability of hyperglycaemia per se to enhance glucose disposal (glucose effectiveness) is also impaired. It is also unclear whether overt diabetes is due to (1) more marked insulin insensitivity; (2) impaired insulin secretion; (3) reduced glucose effectiveness; or (4) a combination of these mechanisms. We used the minimal model to analyse the results of a 3-h intravenous glucose tolerance test to assess glucose effectiveness, insulin sensitivity and insulin responses in 12 non-diabetic cirrhotic patients, 8 diabetic cirrhotic patients and 10 normal control subjects. Fasting blood glucose levels were 4.8±0.2, 7.5±0.6 and 4.7±0.1 mmol/l, respectively. Fasting insulin and C-peptide levels were higher in both cirrhotic patient groups compared with control subjects. The glucose clearance between 6 and 19 min after i.v. glucose was lower in both cirrhotic groups (non-diabetic, 1.56±0.14, diabetic, 0.76±0.06, control subjects, 2.49±0.16 min^–1%, both p<0.001 vs control subjects). Serum insulin peaked at 3 and 23 min in the non-diabetic cirrhotic patients and control subjects; both peaks were higher in the non-diabetic cirrhotic patients and showed a delayed return to basal levels. In the diabetic cirrhotic patients, the first phase insulin and C-peptide response to i.v. glucose was absent; their early (22–27 min) incremental insulin response to i. v. tolbutamide was however similar to that of control subjects but 43% lower than in the non-diabetic cirrhotic patients (p<0.05). Insulin sensitivity was markedly reduced in both cirrhotic groups (non-diabetic, 1.11±0.24×10^–4, diabetic, 0.33±0.53×10^–4, control subjects, 4.37±0.53×10^–4 min^–1 per mU·l^–1, both p<0.001 vs controls). Glucose effectiveness was normal in the non-diabetic cirrhotic patients but 29% lower in the diabetic group. It would appear that overt diabetes develops in those cirrhotic patients who in addition to insulin insensitivity have a marked impairment of insulin secretion. An associated reduction in glucose effectiveness may be a contributory factor.     

Relative roles of insulin and hypoglycaemia on induction of neuroendocrine responses to,symptoms of,and deterioration of cognitive function in hypoglycaemia in male and female humans

Summary To assess the relative roles of insulin and hypoglycaemia on induction of neuroendocrine responses, symptoms and deterioration of cognitive function (12 cognitive tests) during progressive decreases in plasma glucose, and to quantitate glycaemic thresholds, 22 normal, non-diabetic subjects (11 males, 11 females) were studied on four occasions: prolonged fast (n=8, saline euglycaemia study, SA-EU), stepped hypoglycaemia (plasma glucose plateaus of 4.3, 3.7, 3 and 2.3 mmol/l) or euglycaemia during insulin infusion at 1 and 2 mU·kg^–1·min^–1 (n=22, high-insulin hypoglycaemia and euglycaemia studies, HI-INS-HYPO and HI-INS-EU, respectively), and stepped hypoglycaemia during infusion of insulin at 0.35 mU· kg^–1·min^–1 (n=9, low-insulin hypoglycaemia study, LO-INS-HYPO). Insulin per se (SA-EU vs HI-INS-EU), suppressed plasma glucagon (20%) and pancreatic polypeptide (30%), whereas it increased plasma noradrenaline (R10%, p<0.05). Hypoglycaemia per se (HI-INS-HYPO vs HI-INS-EU) induced responses of counterregulatory hormones (CR-HORM), symptoms and deteriorated cognitive function. With the exception of suppression of endogenous insulin secretion, which had the lowest glycaemic threshold of 4.44±0.06 mmol/l, pancreatic polypeptide, glucagon, growth hormone, adrenaline and cortisol had similar glycaemic thresholds (3.8-3.6 mmol/l); noradrenaline (3.1±0.0 mmol/l), autonomic (3.05±0.06 mmol/l) and neuroglycopenic (3.05±0.05 mmol/l) symptoms had higher thresholds. All 12 tests of cognitive function deteriorated at a glycaemic threshold of 2.45±0.06 mmol/l, but 7 out of 12 tests were already abnormal at a glycaemic threshold of 2.89±0.06 mmol/l. Although all CR-HORM had a similar glycaemic threshold, the lag time of response (the time required for a given parameter to increase) of glucagon (15±1 min) and growth hormone (14±3 min) was shorter than adrenaline (19±3 min) and cortisol (39±4 min) (p<0.05). With the exception of glucagon (which was suppressed) and noradrenaline (which was stimulated), insulin per se (HI-INS-HYPO vs LO-INS-HYPO) did not affect the responses of CR-HORM, and did not influence the symptoms or the cognitve function during hypoglycaemia. Despite lower responses of glucagon, adrenaline and growth hormone (but not thresholds) in females than males, females were less insulin sensitive than males during stepped hypoglycaemia.     

Increased hyaluronan production in the glomeruli from diabetic rats: a link between glucose-induced prostaglandin production and reduced sulphated proteoglycan

Summary Exposure in vivo or in vitro to elevated glucose increases production of vasoactive prostaglandins by glomeruli and mesangial cells. This study aimed to determine whether this increased prostaglandin production could provide a link with later structural changes in diabetic nephropathy. Glomerular cores were prepared from control rats and streptozotocin-diabetic rats (3 weeks' duration). Over 24 h in culture hyaluronan production from diabetic glomerular cores was higher than production from control glomerular cores whether maintained in 5.6 mmol/l glucose (105.6±15.5 vs 53.6±8.5 ng hyaluronan per 250 glomerular cores, p<0.001); in 25 mmol/l glucose (149.3±34.8 vs 62.7±7.8 ng hyaluronan per 250 glomerular cores, p<0.01); or in 45 mmol/l glucose (176.8±23.3 vs 102.0±17.9 ng hyaluronan per 250 glomerular cores, p<0.01). At 5.6 mmol/l glucose, exposure in vitro to prostaglandin E₂ caused an increase in hyaluronan production [maximal at 10^–9 mol/l prostaglandin E₂, 237±19 vs 42±4, ng hyaluronan per 250 glomerular cores, p<0.001 (control) and 195±7 vs 103±5, ng hyaluronan per 250 glomerular cores, p<0.001 (diabetic)]. In both control and diabetic glomerular cores hyaluronan production was reduced significantly by the cyclooxygenase inhibitor indomethacin (10^–5 mol/l) [24.7±3.33 vs 40.25±4.11 ng hyaluronan per 250 glomerular cores, p<0.05 (control) and 36.5±6.25 vs 118.0±22.6, p<0.01 (diabetic)]. A direct spectrophotometric microassay was used to determine the concentration of sulphated glycosaminoglycans derived from papain-digested glomerular core proteoglycans. Release of sulphated glycosaminoglycans from diabetic glomerular cores maintained at 5.6 mmol/l glucose was decreased [41.9±1.1 vs 54.0±1.0 g of sulphated glycosaminoglycans (chondroitin sulphate) per 250 glomerular cores p<0.01]. A decrease in sulphated glycosaminoglycans was also shown from control glomerular cores maintained at 25 mmol/l glucose. At this glucose concentration, addition of exogenous hyaluronan or prostaglandin E₂ significantly reduced sulphated glycosaminoglycans from control and diabetic glomerular cores. It is concluded that increased prostaglandin production secondary to high glucose environment can lead to an increased glomerular hyaluronan synthesis. This can substantially affect the levels of sulphated glycosaminoglycans in the extracellular matrix. We propose that these effects provide a possible link between the initial biochemical consequences of hyperglycaemia and later structural changes seen in the glomerulus in diabetes.Abbreviations PG Prostaglandins - GC glomerular cores - STZ-D streptozotocin diabetes - GAG sulphated glycosaminoglycans - PDGF platelet derived growth factor - PGE₂ prostaglandin E₂ - STZ streptozotocin - HSPG heparan sulphate proteoglycan - HA hyaluronan     

The effect of a new specific α-amylase inhibitor on post-prandial glucose and insulin excursions in normal subjects and Type 2 (non-insulin-dependent) diabetic patients

Summary Trestatin (Ro 9-0154), a new specific -amylase inhibitor of microbial origin, was tested in six normal subjects and seven Type 2 (non-insulin-dependent) diabetic patients. In normal subjects the maximal increases in blood glucose following a 115-g starch meal were 2.19±0.57 mmol/l (mean±SEM) with placebo, but 1.32±0.39 mmol/l with 10 mg, 1.06±0.26 mmol/l with 20 mg, 0.43±0.07 mmol/l with 50 mg (p<0.05) and 0.26±0.14 mmol/l with 100 mg (p<0.05) Trestatin. The corresponding increases in plasma insulin were 116.5±19.6mU/l; 74.8±17.5 mU/l; 50.7±8.3 mU/l; 28.7±6.9 mU/l (p<0.05) and 16.5±3.2 mU/l (p<0.05). In the diabetic patients the maximal increases in blood glucose following a 50-g starch meal were 6.09±0.02 mmol/l with placebo, but 3.17±0.59 mmol/ (p<0.05) with 10 mg and 1.69±0.41 mmol/l (p<0.05) with 30 mg Trestatin. The corresponding insulin increases were: 58.8±12.7 mU/l, 31.5±9.7mU/l (p<0.05) and 23.4±4.8 mU/l (p<0.05). Trestatin fully retained this pharmacological activity during treatment for 4 weeks in the diabetic patients. Trestatin did not influence glucose and insulin profiles after oral glucose and sucrose. These results are consistent with a specific inhibition of -amylase in man.     

Paradoxical effects of endogenous and exogenous insulin on amino acid transport activity in the isolated rat pancreas: somatostatin-14 inhibits insulin action

Summary Regulatory effects of insulin, somatostatin and cholecystokinin on amino acid transport in the isolated perfused rat pancreas have been studied using a rapid dual isotope dilution technique. Uni-directional L-serine transport (15 s) was quantified relative to an extracellular tracer D-mannitol over a wide range of substrate concentrations. In pancreata perfused with 2.5 mmol/l D-glucose, a weighted nonlinear regression analysis of overall transport indicated an apparent K_m=14.4±1.6 mmol/l and V_max=25.9±1.4 mol ·min^–1·g^–1 (n=6). Although L-serine transport was stimulated during perfusion with 100 U/ml bovine insulin, endogenous insulin (7–25 ng·min^–1·g^–1) released during continuous perfusion with either 8.8 mmol/l or 16.8 mmol/l D-glucose had no such effect. Exogenous somatostatin-14 (250 pg/ml) or cholecystokinin octapeptide (CCK-8, 3 × 10^–11mol/l) appeared to increase only the K_m for transport. Only CCK-8 evoked a notable protein output (2.9±0.3 mg·30min^–1·g^–1) and juice flow (68±10l·30min^–1·g ^–1, n=3) from the exocrine pancreas. When pancreata were perfused with bovine insulin (100 U/ml) and somatostatin-14 (250 pg/ml), the stimulatory action of exogenous insulin on L-serine transport was abolished. If endogenous insulin and somatostatin, released concurrently in response to 16.8 mmol/l D-glucose, were conveyed to the exocrine epithelium via an islet-acinar portalaxis, it is conceivable that somatostatin modulates the stimulatory action of insulin on basolateral amino acid transport in the exocrine pancreas.     

Effect of glucagon antibodies on plasma glucose,insulin and somatostatin in the fasting and fed rat

Summary A potent high-titre glucagon antibody pool was used to induce a state of acute glucagon deficiency in order to investigate the importance of glucagon in maintaining euglycaemia in the fed and fasted anaesthetised rat. Binding characteristics of the antiserum and evidence of its neutralisation of the biological effects of exogenous glucagon are described. The amount of antibody administered was capable of neutralising up to 12 times the total content of glucagon (approximately 1nmol) in the rat pancreas. The hyperglycaemic response to 1.43 nmol exogenous glucagon was significantly inhibited in the rat by glucagon antibodies given intravenously or intraperitoneally (p < 0.001). However, no changes in plasma glucose occurred in rats fasted 16 h (4.35±0.1 mmol/l or 24 h (4.0±0.05 mmol/l) after antibody administration. The same dose of glucagon antibodies produced no change in plasma glucose (6.1±0.2 mmol/l), immunoreactive insulin (1.85±0.05 g/l) or immunoreactive somatostatin (110±30 ng/l) in rats after antibody administration. Antibody excess, equivalent to a binding capacity for glucagon of 40 nmol/l in the plasma of recipient animals, was demonstrable at all times after passive immunisation. The absence of any affect on glucose concentrations following immunoneutralisation of glucagon suggests that glucagon secretion may not be a major factor in the maintenance of euglycaemia in the rat.