Effect of sustained physiologic hyperinsulinaemia and hyperglycaemia on insulin secretion and insulin sensitivity in man

Summary Two study protocols to examine the effects of chronic (72–96 h) physiologic euglycaemic hyperinsulinaemia (+ 72 pmol/l) and chronic hyperglycaemic (+ 1.4 mmol/l) hyperinsulinaemia (+ 78 pmol/l) on insulin sensitivity and insulin secretion were performed in 15 healthy young subjects. Subjects received a three-step euglycaemic insulin (insulin infusion rates = 1.5, 3, and 6 nmol·kg^–1·min^–1) clamp and a hyperglycaemia (6.9 mmol/l) clamp before and after chronic insulin or glucose infusion. Following 4 days of sustained euglycaemic hyperinsulinaemia whole body glucose disposal decreased by 20–40%. During each insulin clamp step, the defect in insulin action was accounted for by impaired non-oxidative glucose disposal (p<0.01). Chronic euglycaemic hyperinsulinaemia did not alter insulin-mediated suppression of hepatic glucose production. Following insulin infusion the ability of hyperglycaemia to stimulate insulin secretion was significantly diminished. Following 72 h of chronic glucose infusion (combined hyperglycaemic hyperinsulinaemia), there was no change in whole body glucose disposal. However, glucose oxidation during each insulin clamp step was significantly increased and there was a reciprocal decline in non-oxidative glucose disposal by 25–39% (p<0.01); suppression of hepatic glucose production by insulin was unaltered by chronic hyperglycaemic hyperinsulinaemia. Chronic glucose infusion increased the plasma insulin response to acute hyperglycaemia more than twofold. These results demonstrate that chronic, physiologic hyperinsulinaemia, whether created by exogenous insulin infusion or by stimulation of endogenous insulin secretion, leads to the development of insulin resistance, which is characterized by a specific defect in the non-oxidative (glycogen synthetic) pathway. These findings indicate that hyperinsulinaemia should be considered, not only as a compensatory response to insulin resistance, but also as a self-perpetuating cause of the defect in insulin action.Abbreviations NIDDM Non-insulin-dependent diabetes mellitus - CRC Clinical Research Center - Rd rate of glucose disappearance - Ra rate of glucose appearance - HGP hepatic glucose production - NPRQ non-protein respiratory quotient - CV coefficient of variation     

Effect of acute hyperglycaemia and/or hyperinsulinaemia on proinflammatory gene expression,cytokine production and neutrophil function in humans

Aims Type 2 diabetes is frequently associated with infectious complications. Swift activation of leucocytes is important for an adequate immune response. We determined the selective effects of hyperglycaemia and hyperinsulinaemia on lipopolysaccharide (LPS)‐induced proinflammatory gene expression and cytokine production in leucocytes and on neutrophil functions. Methods Six healthy humans were studied on four occasions for 6 h during: (i) lower insulinaemic euglycaemic clamp, (ii) lower insulinaemic hyperglycaemic clamp, (iii) hyperinsulinaemic euglycaemic clamp, and (iv) hyperinsulinaemic hyperglycaemic clamp. Target levels of plasma glucose were 12.0 mmol/l (hyperglycaemic clamps) or 5.0 mmol/l (euglycaemic clamps). Target plasma insulin levels were 400 pmol/l (hyperinsulinaemic clamps) or 100 pmol/l (lower insulinaemic clamps). Results Hyperglycaemia reduced LPS‐induced mRNA expression of nuclear factor of κ light polypeptide gene enhancer in B cells inhibitor alpha (NFKBIA), interleukin‐1 alpha (IL1A) and chemokine (C‐C motif) ligand 3 (CCL3), whereas during hyperinsulinaemia enhanced mRNA levels occurred in six out of eight measured inflammation‐related genes, irrespective of plasma glucose levels. Combined hyperglycaemia and hyperinsulinaemia led to enhanced IL1A, interleukin‐1 beta (IL1B) and CCL3 mRNA levels upon LPS stimulation. Neither hyperglycaemia nor hyperinsulinaemia altered cytokine protein production, neutrophil migration, phagocytic capacity or oxidative burst activity. Conclusions These results suggest that short‐term hyperglycaemia and hyperinsulinaemia influence the expression of several inflammatory genes in an opposite direction, that the acute effects of hyperinsulinaemia on inflammatory mRNA levels may be stronger than those of hyperglycaemia, and that the effects of insulin, in particular, may be relevant in the concurrent presence of hyperglycaemia.     

No glucotoxicity after 53 hours of 6.0 mmol/l hyperglycaemia in normal man

Summary In vitro and in vivo studies have suggested that metabolic deterioration can be induced by hyperglycaemia per se. The effect of 53 h of 2.2 mg glucose · kg ideal body weight^–1· min^–1 was examined in four normal male subjects. This produced overnight hyperglycaemia of 6.0 mmol/l on the two nights of the study compared with 4.7 mmol/l on the control night (p<0.05). In response there was a sustained, two-fold increase in basal plasma insulin (p<0.005) and C-peptide (p<0.05) levels. After two days of hyperglycaemia an increased Beta-cell response was demonstrated in response to an additional glucose infusion stimulus (estimated Beta-cell function median of 84% on the control day to 100% after two days glucose infusion). Plasma insulin and C-peptide responses to a 10.0 mmol/l hyperglycaemic clamp increased over the two days of the study (insulin from median 48 mU/l to 73 mU/l and C-peptide from median 2.0 pmol/ml to 2.6 pmol/ml). Glucose tolerance to the additional glucose infusion stimulus improved, suggesting that the increased insulin response during hyperglycaemia was enhancing peripheral glucose uptake. The calculated peripheral insulin sensitivity was unchanged during the hyperglycaemic clamp. Thus, in response to the two days of basal hyperglycaemia, both the basal and stimulated Beta-cell responses were enhanced and there was no evidence for glucose toxicity to the Beta-cells.     

Relation between glycaemic control,hyperinsulinaemia and plasma concentrations of soluble adhesion molecules in patients with impaired glucose tolerance or Type II diabetes

Aims/hypothesis: Increased plasma concentrations of circulating adhesion molecules in patients with Type II (non-insulin-dependent) diabetes mellitus could be associated with the increased cardiovascular risk in these patients. However, it is controversial whether increased adhesion molecule plasma concentrations are primarily related to hyperglycaemia or to hyperinsulinaemia. Methods: We evaluated the plasma concentrations of soluble E-selectin, intracellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) at baseline and during euglycaemic hyperinsulinaemic clamp in three different groups without additional cardiovascular risk factors: group A (control group), 28 healthy volunteers with normal glucose tolerance; group B, 24 subjects with fasting hyperinsulinaemia, normal fasting glucose but impaired glucose tolerance; group C, 32 patients with Type II diabetes, fasting hyperinsulinaemia and chronic hyperglycaemia. Results: Plasma soluble E-selectin, ICAM-1, and VCAM-1 concentrations were higher (p < 0.05) in patients with Type II diabetes (group C) compared with the other groups. The adhesion molecule concentrations correlate with the fasting plasma glucose (r = 0.59, p < 0.001), the 2-h OGTT plasma glucose (r = 0.70, p < 0.01), and the HbA_{1 c} value (r = 0.61, p < 0.05). The E-selectin but not the ICAM-1 and VCAM-1 plasma concentrations correlated with the fasting insulin concentrations (r = 0.62, p < 0.05) or the whole body glucose uptake (r = 0.59, p < 0.05) in the clamp. The hyperinsulinaemia during the euglycaemic hyperinsulinaemic clamp had no significant effect on the plasma concentrations of E-selectin, ICAM-1, and VCAM-1 in all three groups. Conclusion/interpretation: Our results suggest that increased E-selectin concentrations are related to hyperglycaemia, hyperinsulinaemia and insulin resistance, whereas increased ICAM-1 and VCAM-1 plasma concentrations in patients with Type II diabetes are rather related to hyperglycaemia than to hyperinsulinaemia or insulin resistance. [Diabetologia (2002) 45: 210–216] Received: 13 August 2001 and in revised form: 1 October 2001     

Evidence for a Central Abnormality in the Regulation of Growth Hormone Secretion in Insulin-dependent Diabetes

To assess pituitary and hypothalamic function in diabetes, 100 μg growth hormone releasing factor 1–44 was administered to 10 normal subjects at fasting plasma glucose (5.2 ± 0.1 mmol/l, mean ± S.E.M.), 10 insulin-dependent diabetics while euglycaemic (6.4 ± 0.3 mmol/l), and 10 while hyperglycaemic (13.1 ± 1.3 mmol/l). Six of the diabetics participated in both parts of the study. The normal subjects and euglycaemic diabetics produced similar peaks in growth hormone (118.2 ± 37.6 vs 105.2 ± 23.9 mU/l, p = 0.69). The peak growth hormone level was reached between 30 and 45 minutes in all the normal subjects, but varied between 15 and 75 minutes in the diabetics. While all normal subjects suppress their growth hormone response to releasing factor when hyperglycaemic, not all the diabetics did so, and the suppression did not reach statistical significance on comparison of euglycaemic and hyperglycaemic diabetics (105.2 ± 23.9 vs 64.7 ± 19.4 mU/l, p = 0.2). Comparison of results from those diabetics studied at both euglyaemia and hyperglycaemia again showed no significant difference (140.8 ± 30.9 vs 90.2 ± 27.7 mU/l, p = 0.22). These results suggest a central, possibly hypothalamic, abnormality to account for the disruption of growth hormone regulation in diabetes.     

Sulphonylurea therapy doubles B-cell response to glucose in Type 2 diabetic patients

Summary The effect of sulphonylurea therapy for 3 weeks on glucose-stimulated insulin secretion and insulin resistance was studied in Type 2 diabetic patients. The fasting plasma insulin and C-peptide concentrations on diet alone were compared with each subject's fasting concentrations on sulphonylurea treatment at a lower fasting plasma glucose and at the original diet-alone glycaemic level obtained by the hyperglycaemic clamp technique. At this isoglycaemic level (mean 11 mmol/l), plasma insulin levels increased from 6.9 mU/l on diet alone to 12.1 mU/l on sulphonylurea treatment (p<0.01). The subjects were also studied by the hyperglycaemic clamp technique at mean glycaemic levels of 13 mmol/l before and after sulphonylurea treatment; the incremental insulin response was similarly enhanced from 7.6±3.5 to 13.7±6.9 mU/l (p<0.02) respectively. Sulphonylureas appear to reduce glycaemia by enhancing B-cell function two-fold. In the patients studied this was from approximately 21% to 37% of a normal response. Insulin resistance assessed by the same hyperglycaemic clamps as endogenous plasma insulin concentrations divided by glucose infusion rates was unchanged by sulphonylurea therapy (mean 4.37 compared to 4.40 mU. 1^–1·mg^–1·kg·min on diet alone).     

Intramuscular triglyceride content is increased in IDDM

Summary Increased lipid oxidation is related to insulin resistance. Some of the enhanced lipid utilization may be derived from intramuscular sources. We studied muscle triglyceride (mTG) concentration and its relationship to insulin sensitivity in 10 healthy men (age 29 ± 2 years, BMI 23.3 ± 0.6 kg/m²) and 17 men with insulin-dependent diabetes mellitus (IDDM) (age 30 ± 2 years, BMI 22.8 ± 0.5 kg/m², diabetes duration 14 ± 2 years, HbA_{1 c} 7.7 ± 0.3 %, insulin dose 48 ± 3 U/day). Insulin sensitivity was measured with a 4 h euglycaemic (5 mmol/l) hyperinsulinaemic (1.5 mU or 9 pmol · kg^–1· min^–1) clamp accompanied by indirect calorimetry before and at the end of the insulin infusion. A percutaneous biopsy was performed from m. vastus lateralis for the determination of mTG. At baseline the IDDM patients had higher glucose (10.2 ± 0.9 vs 5.6 ± 0.1 mmol/l, p < 0.001), insulin (40.3 ± 3.2 vs 23.2 ± 4.2 pmol/l, p < 0.01), HDL cholesterol (1.28 ± 0.06 vs 1.04 ± 0.03 mmol/l, p < 0.01) and mTG (32.9 ± 4.6 vs 13.6 ± 2.7 mmol/kg dry weight, p < 0.01) concentrations than the healthy men, respectively. The IDDM patients had lower insulin stimulated whole body total (–25 %, p < 0.001), oxidative (–18 %, p < 0.01) and non-oxidative glucose disposal rates (–43 %, p < 0.001), whereas lipid oxidation rate was higher in the basal state ( + 44 %, p < 0.01) and during hyperinsulinaemia ( + 283 %, p < 0.05). mTG concentrations did not change significantly during the clamp or correlate with insulin stimulated glucose disposal. In healthy men mTG correlated positively with lipid oxidation rate at the end of hyperinsulinaemia (r = 0.75, p < 0.05). In conclusion: 1) IDDM is associated with increased intramuscular TG content. 2) mTG content does not correlate with insulin sensitivity in healthy subjects or patients with IDDM. [Diabetologia (1998) 41: 111–115] Received: 12 June 1997 and in revised form: 8 September 1997     

The sympathetic response to euglycaemic hyperinsulinaemia

Summary Sympathetic nervous system activation by insulin has been suggested as a mechanism explaining the association between insulin resistance and hypertension. We further examined the effect of insulin by direct microneurographic muscle and skin nerve sympathetic activity recordings during euglycaemic insulin clamps in healthy subjects. The mean plasma insulin level was elevated from 5.3±0.7 to 92.2±2.2 mU/l in seven subjects during a 90-min one-step clamp. In six other subjects plasma insulin was further raised from 85.7±4.0 mU/l to 747±53 mU/l between 45–90 min (two-step clamp). Four of the latter subjects received a sham clamp with NaCl infusions only on a second recording session. At the low dose of insulin muscle nerve sympathetic activity increased from a resting level of 22.7±5.0 bursts per min to 27.7±5.0 bursts per min at 15 min (p<0.05). The increases in muscle nerve sympathetic activity were significant (p<0.001; ANOVA) throughout insulin infusion, with a slight further increase (from 29.2±1.6 to 32.3±1.9 bursts per min) at the supraphysiological insulin concentration. During sham clamps muscle nerve sympathetic activity did not increase. Both insulin clamps induced minor, but significant, increases in forearm venous plasma noradrenaline concentrations. Skin nerve sympathetic activity (n=3) did not change during insulin infusions. Heart rate increased slightly but significantly (p<0.005), during the insulin clamps. Blood pressure was not notably affected. In conclusion, hyperinsulinaemia was associated with increased vasoconstrictor nerve activity to skeletal muscle and with no change of sympathetic outflow to skin.     

Insulin induces opposite changes in plasma and erythrocyte magnesium concentrations in normal man

Summary Plasma and erythrocyte magnesium levels were measured by atomic absorption spectrophotometry in 10 healthy volunteers during an oral glucose tolerance test and during an euglycaemic hyperinsulinaemic glucose clamp. At min 180 and 210 of the oral glucose tolerance test, a significant decline in plasma magnesium levels (p < 0.01 andp < 0.05 respectively) and a significant increase in erythrocyte magnesium levels (p < 0.01 andp < 0.05 respectively) were observed. Similar changes were seen during the second hour of the glucose clamp, during which euglycaemia (4.1 ± 0.4 mmol/1) was maintained despite hyperinsulinaemia (110–130 mU/1). During in vitro incubations, glucose (5 mmol/1) did not modify erythrocyte magnesium levels. In contrast, erythrocyte magnesium levels were significantly increased (p < 0.01) by insulin (100 mU/1), an effect entirely abolished by ouabain (5 .10^–4 mol/1). These results suggest that insulin induces a shift of magnesium from the plasma to the erythrocytes both in vivo and in vitro. These data may help to interprete the abnormalities in magnesium circulating levels frequently reported in diabetic patients.     

Glucose inhibits the insulin-induced activation of the insulin-degrading enzyme in HepG2 cells

Aims/hypothesis  Hepatic insulin degradation decreases in type 2 diabetes. Insulin-degrading enzyme (IDE) plays a key role in insulin degradation and its gene is located in a diabetes-associated chromosomal region. We hypothesised that IDE may be regulated by insulin and/or glucose in a liver cell model. To validate the observed regulation of IDE in vivo, we analysed biopsies of human adipose tissue during different clamp experiments in men. Methods  Human hepatoma HepG2 cells were incubated in normal (1 g/l) or high (4.5 g/l) glucose medium and treated with insulin for 24 h. Catalytic activity, mRNA and protein levels of IDE were assessed. IDE mRNA levels were measured in biopsies of human subcutaneous adipose tissue before and at 240 min of hyperinsulinaemic, euglycaemic and hyperglycaemic clamps. Results  In HepG2 cells, insulin increased IDE activity under normal glucose conditions with no change in IDE mRNA or protein levels. Under conditions of high glucose, insulin increased mRNA levels of IDE without changes in IDE activity. Both in normal and high glucose medium, insulin increased levels of the catalytically more active 15a IDE isoform compared with the 15b isoform. In subcutaneous adipose tissue, IDE mRNA levels were not significantly upregulated after euglycaemic or hyperglycaemic clamps. Conclusions/interpretation  Insulin increases IDE activity in HepG2 cells in normal but not in high glucose conditions. This disturbance cannot be explained by corresponding alterations in IDE protein levels or IDE splicing. The loss of insulin-induced regulation of IDE activity under hyperglycaemia may contribute to the reduced insulin extraction and peripheral hyperinsulinaemia in type 2 diabetes.     

Effects of intravenous neuropeptide Y on insulin secretion and insulin sensitivity in skeletal muscle in normal rats

Summary Intracerebroventricular administration of neuropeptide Y to normal rats induces a syndrome characterised by obesity, hyperinsulinaemia, insulin resistance and over expression of the adipose tissue ob gene. Little is known about the effect of circulating neuropeptide Y on glucose metabolism, insulin secretion and leptin. We therefore aimed to evaluate the effect of an intravenous infusion of neuropeptide Y on glucose disposal, endogenous glucose production, whole body glycolytic flux, and glucose storage as assessed during euglycaemic hyperinsulinaemic clamp. In addition, the insulin-stimulated glucose utilisation index in individual tissues was measured by the 2-deoxy-[1-³H]-glucose technique. The effect of neuropeptide Y on insulin secretion was evaluated by hyperglycaemic clamp. Infusion did not induce any change in endogenous glucose production during basal conditions or at the end of the clamp. Glucose disposal was significantly increased in the rats given neuropeptide Y compared with controls (27.8 ± 1.3 vs 24.3 ± 1.6 mg · min^–1· kg^–1; p < 0.05) as was the glycolytic flux (18.9 ± 1.6 vs 14.4 ± 0.8 mg · min^–1· kg^–1; p < 0.05), while glucose storage was comparable in the two groups. In skeletal muscle, the glucose utilisation index was increased significantly in rats given neuropeptide Y. The glucose utilisation index in subcutaneous and epididimal adipose tissue was not significantly different between the two groups. Plasma leptin was significantly increased by hyperinsulinaemia, but was not affected by neuropeptide Y infusion. Both the early and late phase of the insulin response to hyperglycaemia were significantly reduced by neuropeptide Y. In conclusion neuropeptide Y infusion may increase insulin-induced glucose disposal in normal rats, accelerating its utilisation through the glycolytic pathway. Neuropeptide Y reduces both phases of the insulin response to hyperglycaemia. [Diabetologia (1998) 41: 1361–1367] Received: 4 March 1998 and in revised form: 27 May 1998     

In vivo insulin resistance in individual peripheral tissues of the high fat fed rat: assessment by euglycaemic clamp plus deoxyglucose administration

Summary We have examined peripheral insulin action in conscious rats chronically fed high fat (60% calories as fat) or high carbohydrate (lab chow) diets using the euglycaemic clamp plus 3 H-2-deoxyglucose technique. A response parameter of individual tissue glucose metabolic rate (the glucose metabolic index, based on tissue deoxyglucose phosphorylation) was used to assess diet effects in eight skeletal muscle types, heart, lung and white and brown adipose tissue. Comparing high fat with high carbohydrate fed rats, basal glucose metabolism was only mildly reduced in skeletal muscle (only diaphragm was significant,p<0.05), but was more substantially reduced in other tissues (e.g. white adipose tissue 61% and heart 33%). No evidence of basal hyperinsulinaemia was found. In contrast, widespread insulin resistance was found during the hyperinsulinaemic clamp (150 mU/l) in high fat fed animals; mean whole body net glucose utilization was 34% lower (p<0.01), and the glucose metabolic index was lower in skeletal muscle (14 to 56%,p< 0.05 in 6 out of 8 muscles), white adipose (27%,p<0.05) and brown adipose tissue (76%,p<0.01). The glucose metabolic index was also lower at maximal insulin levels in muscle and fat, suggesting the major effect of a high fat diet was a loss of insulin responsiveness. White adipose tissue differed from muscle in that incremental responses (maximal insulin minus basal) were not reduced by high fat feeding. The heart showed an effect opposite to other tissues, with an increase in insulin-stimulated glucose metabolism in high fat versus chow fed rats. We conclude that high fat feeding, without a major increase in body weight or basal hyperinsulinaemia, causes widespread but varying degrees of in vivo insulin resistance in peripheral tissues, with major effects in principally oxidative skeletal muscle.     

Acetyl-salicylic acid impairs insulin-mediated glucose utilization and reduces insulin clearance in healthy and non-insulin-dependent diabetic man

Summary The effect of acetyl-salicylic acid (ASA, 3 g per day for 3 days) on glucose utilization and insulin secretion was studied in healthy volunteers and Type 2 diabetic patients using the hyperglycaemic and euglycaemic insulin clamp technique. When in healthy subjects arterial plasma glucose was acutely raised and maintained at +7 mmol/l above fasting level, the plasma insulin response was enhanced by ASA (70±7 vs. 52±7mU/l), whereas the plasma C-peptide response was identical. Despite higher insulin concentrations, glucose utilization was not significantly altered (control, 61±7; ASA, 65±6mol·kg^–1·min^–1) indicating impairment of tissue sensitivity to insulin by ASA. Inhibition of prostaglandin synthesis was not likely to be involved in the effect of ASA, since insulin response and glucose utilization were unchanged following treatment with indomethacin. In the euglycaemic insulin (1 mU·kg^–1·min^–1) clamp studies, glucose utilization was unaltered by ASA despite higher insulin concentrations achieved during constant insulin infusion (103±4vs. 89±4mU/l). In Type 2 diabetic patients, fasting hyperglycaemia (10.6 ±1.1 mmol/l) and hepatic glucose production (15±2 mol·kg^–1·min^–1) fell upon ASA treatment (8.6±0.7 mmol/l; 13±1 mol·kg^–1· min^–1). During the hyperglycaemic clamp study, the plasma response of insulin, but not of C-peptide, was enhanced by ASA, whereas tissue sensitivity to insulin was reduced by 30 percent. It is concluded that in healthy and Type 2 diabetic man, ASA impairs tissue sensitivity to the action of insulin. This effect is counterbalanced by an augmented plasma insulin response to glucose, which results from a reduced insulin clearance rate. In Type 2 diabetic patients, the reduction in hepatic glucose production may be responsible for the amelioration of hyperglycaemia following ASA treatment.     

Human plasma phospholipid transfer protein activity is decreased by acute hyperglycaemia: studies without and with hyperinsulinaemia in Type 1 diabetes mellitus.

AIMS: Little is known about the regulation of phospholipid transfer protein (PLTP), that plays a key role in lipoprotein metabolism. PLTP secretion may be up-regulated by glucose in vitro, whereas plasma PLTP activity is decreased by exogenous hyperinsulinaemia and glucose-induced hyperinsulinaemia in vivo. In the present study, we evaluated the separate effects of hyperglycaemia and hyperinsulinaemia in C-peptide-negative Type 1 diabetic patients. METHODS: The protocol was carried out in 16 patients (eight females). In each individual, plasma PLTP mass and activity (measured by enzyme-linked immuno-sorbent assay and liposome-high density lipoprotein system, respectively) as well as plasma cholesteryl ester transfer protein (CETP) activity, lipids and apolipoprotein levels were determined at the end of four different glucose clamps, each lasting 210 min: standard insulin (30 mU/kg/h) and standard glucose (glucose 5.0 mmol/l) (SI-SG), standard insulin and high glucose (glucose 12 mmol/l) (SI-HG), high insulin (150 mU/kg/h) and standard glucose (HI-SG), and high insulin and high glucose (HI-HG). RESULTS: Plasma lipids and (apo)lipoproteins, measured at the end of the SI-HG, HI-SG and HI-HG clamps, were not significantly different compared with the levels obtained at the end of the SI-SG clamp. Median plasma PLTP mass and activity at the end of the SI-SG clamp were 12.8 mg/l and 13.2 micromol/ml/h, respectively. Median plasma PLTP mass decreased by 9.1% at the end of the HI-HG clamp (P < 0.01), whereas the changes at the end of the SI-HG and HI-SG clamps were not significant. Median plasma PLTP activity decreased by 5.7, 4.6 and 8.6% at the end of the SI-HG, HI-SG and HI-HG clamps, respectively (all P < 0.05). Median plasma CETP activity was 177 nmol/ml/h at the end of the SI-SG clamp, and decreased by 4.9% (P < 0.05) and by 8.3% (P < 0.05) at the end of the HI-SG and the HI-HG clamps, respectively. Plasma CETP activity did not change significantly at the end of the SI-HG clamp. CONCLUSIONS: The present study demonstrates that plasma PLTP activity is independently decreased by acute hyperglycaemia and hyperinsulinaemia in humans in vivo. These data do not support a direct role of short-term hyperglycaemia in up-regulating plasma PLTP levels.     

Metabolic Effects of Pindolol and Propranolol in a Double-Blind Cross-Over Study in Hypertensive Patients

Metabolic effects of pindolol and propranolol were investigated in a randomised study of double-blind, double-dummy design in 39 Caucasians with newly detected hypertension. Each active treatment period was 6 months long. A euglycaemic hyperinsulinaemic clamp test was done to measure insulin sensitivity, and i.v. glucose tolerance was investigated with insulin determinations. Lipoprotein concentrations were quantified and lipoprotein lipase activities were determined in muscle and adipose tissue and in plasma after heparin injection. The blood pressure was significantly reduced by both regimes. The insulin sensitivity index was decreased by 34% during propranolol treatment and by 17% during pindolol treatment. The insulin concentrations in plasma were elevated at the end of the i.v. glucose tolerance test but were not high enough to compensate for the insulin resistance, so HbA_Ic and glucose concentrations were increased. A significant reduction of lipoprotein lipase activity in skeletal muscle during propranolol treatment probably explains the pronounced increase in serum triglyceride concentration during propranolol treatment despite lower free fatty acids and higher lipoprotein lipase activity in adipose tissue. These changes of lipoprotein lipase activity were not correlated to the changes in insulin sensitivity. In summary, the metabolic effects were significantly less pronounced with pindolol than with propranolol, which probably can be ascribed to the agonistic effect of pindolol on beta₂ adrenoceptors.     

Simple empirical assessment of Beta-cell function by a constant infusion of glucose test in normal and Type 2 (non-insulin-dependent) diabetic subjects

Summary The plasma insulin or C-peptide response to a 90-min constant glucose infusion 5 mg · kg ideal body weight^–1·min^–1 provides Beta-cell assessment comparable to more intensive methods. In 14 diet-treated Type 2 (non-insulin-dependent) diabetic subjects and 12 non-diabetic subjects, plasma insulin and C-peptide concentrations gave near linear plots against simultaneous glucose values. The glucose-insulin and glucose-C-peptide vectors (G-I and G-C vectors), could be extrapolated to predict insulin and C-peptide levels during a 12 mmol/l hyperglycaemic clamp. Predicted concentrations correlated with clamp concentrations, r = 0.94 and r = 0.98 respectively, p<0.001, validating the vectors as empirical glucose dose-response curves. The vector slopes correlated highly with % Beta, a mathematical model-derived measure of Beta-cell function using constant infusion of glucose model assessment, Spearman r = 0.95 and 0.93 for insulin and C-peptide, respectively. G-I vector slopes in 21 diet-treated Type 2 diabetic subjects with fasting glucose (mean +1 SD) 7.5±2,3 mmol/1, were lower than in 28 non-diabetic subjects, (geometric mean, 1 SD range, 8.4 pmol/mmol (3.3–21.0) and 25.1 pmol/mmol (14.3–44.1), p<0.001, respectively), indicating an impaired Beta-cell response. The G-I vector slopes correlated with obesity in both groups (r = 0.54 p<0.02 and 0.72, p<0.001 respectively), and, in 15 non-diabetic subjects, correlated inversely with insulin sensitivity as measured by a euglycaemic clamp (r = –0.66, p<0.01).Thus,Beta-cell function needs to be interpreted in relation to obesity/insulin resistance and, taking obesity into account, only 4 of 21 diabetic patients had Betacell function (G-I vector slope) in the non-diabetic range. The fasting plasma glucose in the diabetic subjects correlated inversely with the obesity-corrected G-I and G-C vector slopes (partial r = –0.57, p <0.01 and –0.86, p<0.001, respectively). The insulin or C-peptide response to the glucose infusion provides a direct empirical measure of the Beta-cell function, which can be interpreted in relation to obesity or to insulin resistance to assess underlying pancreatic responsiveness.     

Changes of lipolytic enzymes cluster with insulin resistance syndrome

Summary The activities of hepatic and lipoprotein lipase and the levels of lipo- and apoproteins were compared in two groups of normoglycaemic men representing the highest (n=18) and lowest (n=15) fasting insulin quintiles of first degree male relatives of non-insulin-dependent diabetic patients. The high insulin group representing insulin-resistant individuals had significantly lower post-heparin plasma lipoprotein lipase activity than the low insulin group (14.2±4.0 vs 20±5.8 mol NEFA·ml^–1·h^–1, p<0.001); hepatic lipase activity did not differ between the two groups (24.2±11 vs 18.0±5.3 mol NEFA·ml^–1·h^–1, NS). The lipoprotein lipase/hepatic lipase ratio in the high insulin group was decreased by 66% as compared to the low insulin group (0.75±0.57 vs 1.25±0.65, p<0.01). In the high insulin group both total and VLDL triglycerides were higher than in the low insulin group (1.61±0.57 vs 0.86±0.26 mmol/l, p< 0.001 and 1.00±0.47 vs 0.36±0.16 mmol/l, p<0.001, respectively) whereas HDL cholesterol and HDL₂ cholesterol were lower (1.20±0.30 vs 1.43±0.22 mmol/l, p<0.05 and 0.49±0.21 vs 0.71±0.17 mmol/l, p<0.05, respectively). Total cholesterol, LDL cholesterol or HDL₃ cholesterol did not differ between the two groups. The mean particle size of LDL was smaller in the high insulin group than in the low insulin group (258±7 vs 265±6 å, p<0.05). We propose that the changes of lipoprotein lipase and lipoprotein lipase/hepatic lipase ratio cluster with insulin resistance and provide a possible mechanism to explain the lowering of HDL cholesterol and elevation of triglyceride concentrations observed in insulin-resistant subjects.Abbreviations LPL Lipoprotein lipase - HL hepatic lipase - VLDL very low density lipoprotein - IDL intermediate density lipoprotein - LDL low density lipoprotein - HDL high density lipoprotein - chol cholesterol - TG triglycerides - NEFA non-esterified fatty acids     

Hyperinsulinaemia is Associated with Stimulation of Cholesterol Synthesis in Both Type 1 and Type 2 Diabetes

The effect of hyperinsulinaemia and hyperglycaemia on cholesterol synthesis was examined in lymphocytes from diabetic subjects. The first part of the study involved the provocation of hyperinsulinaemia by consumption of a carbohydrate-rich meal, in obese patients with Type 2 diabetes mellitus. Cholesterol synthesis was measured before and 4 h after completing the meal. Results were compared to groups of obese non-diabetic patients and to control subjects. Analysis of the three groups demonstrated that the percentage change in cholesterol synthesis was directly proportional to the percentage rise in serum insulin (r = 0.49, p < 0.05). This physiological study demonstrated that postprandial hyperinsulinaemia promoted cholesterol synthesis; however, we could not estimate the effect of the meal on cholesterologenesis. To study hyperinsulinaemia in isolation, we examined the effects of varying insulin infusion rates for 4 h at either low or high levels of serum glucose using the glucose clamp technique in young Type 1 diabetic patients. Cholesterol synthesis in lymphocytes was again measured before and after the study period. Hyperinsulinaemia stimulated cholesterol synthesis (+28.6%, p < 0.05) but hyperglycaemia alone did not exhibit this effect (-1.7% NS). The combination of hyperinsulinaemia and hyperglycaemia produced the greatest increase in cholesterol synthesis (+ 51.4%, p < 0.05) but this increase was not significantly different from hyperinsulinaemia alone. The percentage increase in serum insulin levels was again proportional to the percentage change in cholesterol synthesis (r = 0.46, p < 0.05).     

Partial recovery of insulin secretion and action after combined insulin-sulfonylurea treatment in Type 2 (non-insulin-dependent) diabetic patients with secondary failure to oral agents

Summary Metabolic control, insulin secretion and insulin action were evaluated in seven Type 2 (non-insulin-dependent) diabetic patients with secondary failure to oral antidiabetic agents before and after two months of combined therapy with supper-time insulin (Ultratard: 0.4 U/kg body weight/day) plus premeal glibenclamide (15 mg/day). Metabolic control was assessed by 24 h plasma glucose, NEFA, and substrate (lactate, alanine, glycerol, ketone bodies) profile. Insulin secretion was evaluated by glucagon stimulation of C-peptide secretion, hyperglycaemic clamp (+7 mmol/l) and 24 h free-insulin and C-peptide profiles. The repeat studies, after two months of combined therapy, were performed at least 72 h after supper-time insulin withdrawal. Combining insulin and sulfonylurea agents resulted in a reduction in fasting plasma glucose (12.9±7 vs 10.4±1.2 mmol/l; p<0.05) and hepaic glucose production (13.9±1.1 vs 11.1±1.1 mol·kgc-min^–1; p<0.05). Mean 24 h plasma glucose was also lower (13.7±1.2 vs 11.1±1.4 mmol/l; p<0.05). Decrements in fasting plasma glucose and mean 24 h profile were correlated (r=0.90; p<0.01). HbA_1c also improved (11.8±0.8 vs 8.9±0.5%; p<0.05). Twenty-four hour profile for NEFA, glycerol, and ketone bodies was lower after teatment, while no difference occurred in the blood lactate and alanine profile. Insulin secretion in response to glucagon (C-peptide =+0.53±0.07 vs +0.43±0.07 pmol/ml) and hyperglycaemia (freeinsulin = 13.1±2.0 vs 12.3±2.2 mU/l) did not change. On the contrary, mean 24 h plasma freeinsulin (13.2±2.6 vs 17.5±2.2 mU/l; p<0.01) and C-peptide (0.76±0.10 vs 0.98±0.13 pmol/l; p<0.02) as well as the area under the curve (19.1±4.1 vs 23.6±3.1 U/24 h;p<0.01 and 1.16±0.14 vs 1.38±0.18 mol/24 h; p<0.02 respectively) were significantly increased. The ratio between glucose infusion (M) and plasma insulin concentration (I) during the hyperglycaemic clamp studies (M/I, an index of insulin sensitivity), was not statistically different (1.40±0.25 vs 1.81±0.40 mol·kg^–1· min^–1/mU·l^–1). These data suggest that, in Type 2 diabetic patients with secondary failure to oral antidiabetic agents, the combination of supper-time longacting insulin and premeal sulfonylurea agents can improve metabolic control. This positive effect is possibly mediated through an increased secretion of insulin in response to physiologic stimuli.     

Type 2 diabetes mellitus — genes or intrauterine environment? An embryo transfer paradigm in rats

Aims/hypothesis The familial predisposition to Type 2 diabetes mellitus is mediated by both genetic and intrauterine environmental factors. In the normal course of events, maternal genes always develop in the same uterus, thus restricting studies aimed at investigating the relative contribution of these factors. We have developed an embryo transfer paradigm in rats to overcome this difficulty.Methods Euglycaemic female Wistar rats were superovulated and mated with male Wistar rats. The following day, fertilised eggs were transferred into pseudo-pregnant female Wistar rats or hyperglycaemic Goto Kakizaki (GK) rats. Pregnancies were allowed to go to term. Offspring were weighed at 6 weeks, 3 months and 6 months of age and an intravenous glucose tolerance test was carried out at 6 months of age.Results Offspring from Wistar into Wistar embryo transfers (n=20) were not significantly hyperglycaemic compared to the non-manipulated Wistar stock colony (n=26). However, offspring from Wistar gametes reared in hyperglycaemic GK mothers (n=51) were significantly lighter at 6 weeks of age (156±4.1 g vs 180±6.1 g [mean ± SEM], p<0.01) and significantly more hyperglycaemic at 6 months of age (fasting glucose 6.6±0.18 mmol/l vs 4.8±0.21 mmol/l, mean blood glucose during glucose tolerance test 14.3±0.31 mmol/l vs 11.1±0.28 mmol/l, p<0.01) than Wistar gametes transferred back into euglycaemic Wistar mothers. When GK rats were superovulated and mated together, transfer of 1-day-old embryos into pseudo-pregnant Wistar dams did not alleviate hyperglycaemia in adult offspring.Conclusions/interpretation In GK rats, a euglycaemic intrauterine environment cannot overcome the strong genetic predisposition to diabetes. However, in Wistar rats with a low genetic risk of diabetes, exposure to hyperglycaemia in utero significantly increases the risk of diabetes in adult life.Abbreviations AvGTT weighted average blood glucose during glucose tolerance test - FG fasting blood glucose - GK Goto Kakizaki - W Wistar