Insulin Deficiency Rather Than Hyperinsulinaemia in Newly Diagnosed Type 2 Diabetes Mellitus

This paper reports beta cell function as assessed during OGTT using specific IRMAs for insulin, intact and 32/33 split proinsulin in subjects with newly diagnosed Type 2 diabetes matched to normal controls. The relationships between insulin and the proinsulins to risk factors for cardiovascular disease were also examined. Similar fasting insulin concentrations but lower 30-min post-glucose-load insulin concentrations were found in diabetic subjects (mean ± SEM 143 ± 12 pmol^?1 vs 304 ± 19 (p < 0.001). Subjects with diabetes had increased fasting intact (10.6 ± 1.1 pmol^?1 vs 3.3 ± 0.2, p < 0.001) and 32/33 split proinsulin concentrations (8.1 ± 0.9 pmol^?1 vs 2.2 ± 0.3, p < 0.0001). Beta cell dysfunction, as expressed by a reduction in the 30-min insulin to glucose ratio (9.4 ± 1 vs 34.8 ± 2.3, p < 0.0001) and an increase in the fasting percentage of total proinsulin-like to total insulin-like molecules (24.5 ± 9% vs 11.6 ± 5, p < 0.001), was present in subjects with diabetes. In diabetic subjects beta cell dysfunction and insulin deficiency increased relative to the degree of fasting hyperglycaemia. It seems clear that beta cell dysfunction and insulin deficiency are major features of Type 2 diabetes. Only the fasting concentration of 32/33 split proinsulin positively correlated with both the waist/hip ratio (r = 0.36, p < 0.001), diastolic blood pressure (r = 0.23, p < 0.01) in addition to plasma triglyceride concentration (r = 0.46, p < 0.001). It is questionable whether hyperinsulinaemia plays a pathogenic role in cardiovascular disease in subjects with glucose intolerance.     

Evidence for Impaired Pancreatic Beta Cell Function in South African Indians with Impaired Glucose Tolerance

In a prospective study of South African Indians with impaired glucose tolerance (IGT), the serum insulin response during a 75 g oral glucose tolerance test (OGTT) was examined in 128 subjects who were classified as IGT 1 year previously (year 0) and in 60 matched control subjects. Based on the results at year 1, study subjects were divided into three groups, using World Health Organization criteria for glucose tolerance: IGT (n = 47), diabetes (n = 41), and transient IGT (normal glucose tolerance) (n = 40). When compared with the control group, despite higher plasma glucose concentrations, the IGT group showed similar fasting insulin, but lower 30-min insulin response (57.4 ± 1.9 mUI^?1 vs 86.5 ± 1.8, p<0.001) and lower 30-min insulin/glucose ratio (7.4 ± 5.2 vs 13.3 ± 8.7, p < 0.001). The insulinogenic index was lower in the IGT group than in the control group at 30, 60, 90, and 120 min (p < 0.01, p < 0.001, p < 0.001, p < 0.001, respectively). The 2-h insulin response was higher in the IGT group (106.7 ± 1.9 mUI^?1 vs 59.2 ± 1.9, p < 0.01). The IGT group displayed a delayed pattern of insulin response with maximum levels only at 2-h. Insulin area was similar in the two groups. In the transient IGT group, despite similar plasma glucose levels, the insulin responses at 0, 15, 30, and 60 min (p < 0.01, p < 0.001, p < 0.001, p < 0.001, respectively) were lower than in the control group; the 30-min insulin/glucose ratio (7.1 ± 5.1 vs 13.3 ± 8.7, p < 0.001) and 60-min insulinogenic index (46.9 ± 86.3 vs 123.4 ± 206.3, p < 0.001) were also lower in the transient IGT group. This study has shown that IGT in South African Indians is characterized by a diminished early phase insulin response and delayed (2-h) hyperinsulinaemia during OGTT. Such findings would suggest that in this population group impaired early beta cell function is an important pathophysiological abnormality underlying IGT.     

Increased Maternal Fasting Proinsulin as a Predictor of Insulin Requirement in Women with Gestational Diabetes

Circulating proinsulin was assessed during a 75g OGTT in 55 pregnant women who fulfilled WHO criteria for impaired glucose tolerance before the 32nd gestational week. Proinsulin was assayed retrospectively using a two-site immunoradiometric assay and immunoreactive insulin by radioimmunoassay. Of the 55 women, 19 required insulin treatment in addition to diet later in pregnancy. Fasting proinsulin concentrations were significantly higher in the 19 women who later required insulin treatment compared with the 36 women treated with diet alone (3.4 ± 0.7 vs 1.8 ± 0.2 pmol l^?1, p < 0.005). There was no difference between the treatment groups of 60 and 120 min proinsulin values during the OGTT. Fasting plasma glucose and immunoreactive insulin were similar in the insulin-treated and diet-treated women and remained similar during the OGTT. No women within the insulin-treated group had a fasting plasma proinsulin value < 1.1 pmol l^?1 in contrast with 12 women in the diet-treated group (p = 0.0123). Ten of the 19 insulin-treated women had a fasting plasma proinsulin > 2.5 pmol l^?1 compared with 8 of the 36 diet-treated women (p = 0.0346). Fasting proinsulin values early in pregnancy have prognostic implications in women with gestational diabetes.     

Plasminogen Activator Inhibitor (PAI-1) Activity is Elevated in Asian and Caucasian Subjects with Non-insulin-dependent (Type 2) Diabetes but not in Those with Impaired Glucose Tolerance (IGT) or Non-diabetic Asians

In order to study the plasminogen activator inhibitor activity (PAI-1) in subjects at different risk of non-insulin-dependent diabetes and ischaemic heart disease we examined 89 subjects with diet controlled NIDDM (49 Caucasian, 40 Asian), 29 with impaired glucose tolerance (IGT) (13 Caucasian, 16 Asian), and 149 with normal glucose tolerance (67 Caucasian, 82 Asian). Diabetes was diagnosed by WHO criteria and highly specific, monoclonal antibody-based assays were used to measure insulin, intact proinsulin, and des 31,32 proinsulin. Subjects with NIDDM were significantly more obese, had more central distribution of obesity, higher fasting plasma specific insulin concentrations (NIDDM median 74 pmol l⁻¹ vs IGT 41 pmol l⁻¹, p < 0.01 and vs normals 34 pmol l⁻¹, p < 0.001) and higher PAI-1 activity than normals and those with IGT (NIDDM 23.0 ± 6.9 vs IGT 16.8 ± 5.0, p < 0.001 and vs normals 17.1 ± 6.9 AU ml⁻¹, p < 0.001). However, PAI-1 activity was not significantly different between Asian and Caucasian normals (17.5 ± 7.3 vs 16.5 ± 6.4 AU ml⁻¹, p = ns) and diabetic (22.8 ± 7.3 vs 23.1 ± 6.6 AU ml⁻¹, p = ns) subjects. In addition to relationships with obesity and plasma triglyceride, PAI-1 activity, after controlling for age, sex, body mass index, and waist–hip ratio, was related to fasting insulin (partial r = 0.22, p < 0.001), intact proinsulin (partial r = 0.36, p < 0.001), and des 31,32 proinsulin concentrations (partial r = 0.33, p < 0.001) as measured by highly specific assays. The association of PAI-1 with diabetes was weakened but remained statistically significant (p = 0.042) after controlling for age, sex, ethnicity, obesity, plasma triglyceride, and all insulin-like molecules. We conclude that, although PAI-1 activity is raised in subjects with diet-treated NIDDM, it is normal in subjects with IGT and non-diabetic Asians, populations at high risk of NIDDM and ischaemic heart disease. Raised PAI-1 activity may play an important role in the pathogenesis of macrovascular disease in subjects with NIDDM, but is unlikely to explain excess risk of ischaemic heart disease in Asians and those with impaired glucose tolerance.     

Effect of Sulphonylurea Therapy on Plasma Insulin,Intact and 32/33 Split Proinsulin in Subjects with Type 2 Diabetes Mellitus

This study was undertaken to clarify the effect of sulphonylurea therapy on beta cell function in 27 subjects with newly diagnosed Type 2 diabetes mellitus. Plasma glucose, insulin, intact and 32/33 split proinsulin were measured at diagnostic OGTT. After 8–12 weeks on a conventional diet, subjects with a fasting glucose > 9 mmol I^?1 (n = 12) were commenced on sulphonylurea therapy. At diagnosis, the sulphonylurea requiring group were more hyperglycaemic (p < 0.0001), less obese (p<0.05) and more insulin deficient with a lower 30 min insulin (p < 0.0002) than the diet group. Following dietary intervention in the sulphonylurea group, weight remained unchanged but there was a reduction in fasting glucose (p < 0.009). Fasting insulin, intact proinsulin, and 32/33 split proinsulin remained unchanged. After 12 weeks of sulphonylurea therapy there was a weight gain of 1.5 kg (p < 0.01), but a reduction in fasting glucose (p < 0.0001). Fasting insulin and intact proinsulin increased (p < 0.004) but 32/33 split proinsulin remained unchanged. There was a significant increase in both the fasting insulin to glucose ratio (p < 0.005), and the intact to 32/33 split proinsulin ratio (p < 0.02). Final fasting glucose following sulphonylurea therapy was positively correlated with the initial intact and 32/33 split proinsulin and the fasting glucose following dietary treatment. It is clear from this work that sulphonylureas have a complex effect on beta cell physiology and as well as stimulating release of insulin they increase the release of intact proinsulin but not that of 32/33 split proinsulin, hence they increase the intact to 32/33 split proinsulin ratio.     

Determinants of glucose tolerance in impaired glucose tolerance at baseline in the Actos Now for Prevention of Diabetes (ACT NOW) study

Aims/hypothesis

The aim of the study was to examine the determinants of oral glucose tolerance in 602 persons with impaired glucose tolerance (IGT) who participated in the Actos Now for Prevention of Diabetes (ACT NOW) study.

Methods

In addition to the 602 IGT participants, 115 persons with normal glucose tolerance (NGT) and 50 with impaired fasting glucose (IFG) were identified during screening and included in this analysis. Insulin secretion and insulin sensitivity indices were derived from plasma glucose and insulin during an OGTT. The acute insulin response (AIR) (0–10 min) and insulin sensitivity (S_I) were measured with the frequently sampled intravenous glucose tolerance test (FSIVGTT) in a subset of participants.

Results

At baseline, fasting plasma glucose, 2 h postprandial glucose (OGTT) and HbA_1c were 5.8?±?0.02 mmol/l, 10.5?±?0.05 mmol/l and 5.5?±?0.04%, respectively, in participants with IGT. Participants with IGT were characterised by defects in early (?I _0–30/?G _0–30?×?Matsuda index, where ?I is change in insulin in the first 30 min and ?G is change in glucose in the first 30 min) and total (?I_0–120/?G_0–120?×?Matsuda index) insulin secretion and in insulin sensitivity (Matsuda index and S_I). Participants with IGT in whom 2 h plasma glucose was 7.8–8.3 mmol/l had a 63% decrease in the insulin secretion/insulin resistance (disposition) index vs participants with NGT and this defect worsened progressively as 2 h plasma glucose rose to 8.9–9.94 mmol/l (by 73%) and 10.0–11.05 mmol/l (by 80%). The Matsuda insulin sensitivity index was reduced by 40% in IGT compared with NGT (p?<?0.005). In multivariate analysis, beta cell function was the primary determinant of glucose AUC during OGTT, explaining 62% of the variance.

Conclusion

Our results strongly suggest that progressive beta cell failure is the main determinant of progression of NGT to IGT.     

A Higher Proinsulin Response to Glucose Loading Predicts Deteriorating Fasting Plasma Glucose and Worsening to Diabetes in Subjects with Impaired Glucose Tolerance

To evaluate the clinical significance of proinsulin determination, we measured glucose, insulin, C-peptide and proinsulin during 75-g oral glucose loading in 59 patients. In a 2.5-year follow-up study of 37 subjects with impaired glucose tolerance (IGT) at the initial test, 11 patients changed from IGT to a normal state and 5 patients showed worsening to overt Type 2 diabetes with elevation of fasting plasma glucose; 21 patients remained unchanged. Although our data showed that both fasting (IGT: p = 0.4523) and 120-min plasma glucose (IGT: p = 0.8168) values at the initial test were not significantly correlated with increased fasting plasma glucose levels in a 2.5-year follow-up study, subjects with a higher 120-min proinsulin response to glucose during the initial OGTT showed a significant correlation (IGT: p <0.0001) with increased fasting plasma glucose levels after follow-up period and developed Type 2 diabetes. The present findings suggest that the proinsulin response to glucose loading might be a useful indicator for predicting worsening to diabetes in subjects with impaired glucose tolerance.     

Impaired glucose tolerance (IGT) is associated with reduced insulin-induced suppression of glucagon concentrations

Aims/hypothesis: We aimed to examine whether impaired glucose tolerance is associated with reduced suppression of glucagon concentrations. Methods: Eighty-four non-diabetic women of Caucasian origin and 61 years of age, of whom 48 had normal glucose tolerance (NGT) and 36 had IGT, underwent a 75 g OGTT and a hyperinsulinaemic, euglycaemic clamp with measurement of glucagon, insulin and glucose concentrations. Results: At 2 h after 75 g oral glucose, glucagon concentrations were reduced by 7.1 ± 1.1 ng/l in NGT vs 8.0 ± 1.4 ng/l in IGT, (NS). However, the 2 h reductions in glucagon per mmol/l increase in 2 h glucose or per pmol/l increase in 2 h insulin were both impaired in IGT (p = 0.002 and p = 0.043, respectively) because the 2 h increases in glucose and insulin were higher in IGT than in NGT. Furthermore, suppression of glucagon concentrations during a euglycaemic clamp at hyperinsulinaemic concentrations (NGT: 607 ± 19 pmol/l, IGT: 561 ± 21 pmol/l) was lower in IGT (13.6 ± 1.6 ng/l) than in NGT (23.1 ± 1.2 ng/l; p < 0.001). The suppression of glucagon concentrations during the hyperinsulinaemic, euglycaemic clamp correlated with insulin sensitivity (r = 0.24, p = 0.027) and with the 2 h glucose value during the OGTT (r = –0.52, p < 0.001). Conclusion/interpretation: Impaired glucose tolerance is associated with reduced insulin-induced suppression of glucagon secretion, which could be caused by A-cell insulin resistance. Inappropriately high glucagon secretion could therefore contribute to the metabolic perturbations in IGT. [Diabetologia (2001) 44: 1998–2003] Received: 15 May 2001 and in revised form: 13 July 2001     

Loss of the First Phase Insulin Response to Intravenous Glucose in Subjects with Persistent Impaired Glucose Tolerance

Loss of the first phase insulin response to intravenous glucose is one of the earliest detectable defects of beta cell dysfunction in Type 2 diabetes mellitus. Impaired glucose tolerance (IGT) is considered a prediabetic condition, therefore loss of first phase insulin secretion in subjects with IGT would suggest beta cell dysfunction as an early lesion in the development of Type 2 diabetes. Three groups of subjects were studied, 7 subjects with persistent IGT (classified as having IGT at two 75 g oral glucose tolerance tests (OGTT) done 6 months apart), 6 subjects with transient IGT (IGT at the first OGTT, but normal glucose tolerance at a repeat OGTT 6 months later), and 7 normal controls. First phase insulin secretion was studied using an intravenous glucose tolerance test with arterialized blood sampling. Fasting, 3, 4 and 5 min samples were assayed for glucose and insulin (specific two-site immunoradiometric assay). The fasting insulin was similar in all three groups, however the 3 min insulin response was significantly lower in those with persistent impaired glucose tolerance (p < 0.02). Thus subjects with persistent impaired glucose tolerance demonstrated loss of the first phase insulin response as an early indicator of beta cell dysfunction while subjects with transient IGT had a normal insulin response to intravenous glucose. During the OGTT, the 30 min glucose was not significantly different (p = 0.1) but the 30 min insulin to glucose ratio was significantly lower in subjects with persistent IGT (p < 0.03). In the whole group the 30 min insulin to glucose ratio during the OGTT showed a significant correlation with the peak insulin response during the IVGTT (r = 0.76, p < 0.001). This study suggests that beta cell dysfunction with impaired early insulin release is present before the development of Type 2 diabetes.     

Insulin Secretion and Sensitivity in Women Fulfilling WHO Criteria for Gestational Diabetes

Abnormalities of insulin secretion rather than insulin sensitivity are described in women fulfilling the American criteria for gestational diabetes. We examined insulin secretion and insulin sensitivity in 38 women at risk of gestational diabetes categorized according to the less stringent WHO criteria, based on the 75 g oral glucose tolerance test, performed at 24 weeks gestation. Insulin sensitivity was assessed at 28 and 36 weeks using the short insulin tolerance test. Applying WHO criteria, 18 women had GDM. Age and body mass index of the GDM and glucose tolerant women were similar (32.4 ± 1.1 (SE) vs 32.3 ± 1.9 yr; 28.7 ± 1.5 vs 28.8 ± 1.7 kg m^-2, respectively). Fasting glucose was higher in the GDM women than controls (5.1 ± 0.2 vs 4.5 ± 0.1 mmol l^-1, p<0.025) while fasting insulin was similar (75 ± 18 vs 90 ± 16 pmol l^-1). The 30-min insulin concentration during the OGTT was lower in the GDM women than controls (436 ± 61 vs 788 ± 152 pmol l^-1, p< 0.05), while the insulin sensitivity at 28 (87 ± 5 vs 76 ± 5 μmol l^-1 min) and 36 weeks (73 ± 8 vs 76 ± 8 μmol l^-1 min) was similar. A negative correlation existed between the 30-min insulin and 120-min glucose concentration during the OGTT (Rho -0.328, p<0.05). The WHO criteria for GDM identify women with similar abnormalities of insulin secretion as the more stringent American criteria.     

Insulin secretory responses to rising and falling glucose concentrations are delayed in subjects with impaired glucose tolerance

Aims/hypothesis. We hypothesized that beta-cell responses to changes in glucose would not be normal in subjects with impaired glucose tolerance (IGT). Methods. Three groups of 6 subjects were studied: normal weight with normal glucose tolerance (control subjects); obese with normal glucose tolerance (Obese-NGT); and obese with IGT (Obese-IGT). All subjects had a graded glucose infusion protocol to increase (step-up) and then decrease (step-down) plasma glucose. We obtained average insulin-secretion rates (ISR) over the glucose range common to all three groups during step-up and step-down phases, minimal model indices of beta-cell function (f_b, f_d, f_s, T_up, T_down ), and insulin sensitivity (Si). Results. ISR differed significantly between step-up and -down phases only in Obese-IGT individuals. Basal (f_b) and stimulated (f_d, f_s) beta-cell sensitivity to glucose were similar in the three groups. Delays between glucose stimulus and beta-cell response during both step-up (T_up) and -down (T_down) phases were higher in Obese-IGT compared to Controls and Obese-NGT individuals. The product ISR × Si (10^–5·min^–2× l) was lower in Obese-IGT compared to Controls, both during step-up (919 ± 851 vs 3192 ± 1185, p < 0.05) and step-down (1455 ± 1203 vs 3625 ± 691, p < 0.05) phases. Consistently, the product f_s× Si (10^–14·min^–2· pmol^–1× l) was lower in Obese-IGT than in control subjects (27.6 ± 25.4 vs 103.1 ± 20.2, p < 0.05). Conclusion/interpretation. Subjects with IGT are not able to secrete insulin to compensate adequately for insulin resistance. They also show delays in the timing of the beta-cell response to glucose when glucose levels are either rising or falling. [Diabetologia (2002) 45: ▪–▪] Received: 30 July 2001 and in revised form: 21 November 2001     

Immunoradiometric assay of insulin,intact proinsulin and 32–33 split proinsulin and radioimmunoassay of insulin in diet-treated Type 2 (non-insulin-dependent) diabetic subjects

Summary Plasma insulin, intact proinsulin and 32–33 split proinsulin measured by specific immunoradiometric assays and insulin and C-peptide measured by radioimmunoassay were measured during a constant infusion of glucose test in ten diet-treated subjects with a history of Type 2 (non-insulin-dependent) diabetes (termed diabetic subjects), mean fasting plasma glucose 6.0 ± 1.0 mmol/l (mean ± SD), and 12 non-diabetic control subjects. Immunoreactive insulin concentrations measured by radioimmunoassay were 33 higher than insulin and 16 % higher than the sum of insulin and its precursors by immunoradiometric assay. The diabetic and non-diabetic subjects had similar fasting concentrations of insulin, intact proinsulin and 32–33 split proinsulin. The ratio of fasting intact proinsulin to total insulin was greater in the diabetic than the non-diabetic group 12.0 % (6.8–21.0 %, 1 SD range) and 6.3 % (4.0–9.8 %), respectively,p < 0.01), though the groups overlapped substantially. After glucose infusion, diabetic and non-diabetic subjects had similar intact proinsulin concentrations (geometric mean 4.9 and 5.2 pmol/l, respectively), but the diabetic group had impaired insulin secretion by immunoradiometric assay (geometric means 55 and 101 pmol/1,p < 0.05) or by radioimmunoassay C-peptide (geometric means 935 and 1410 pmol/1,p < 0.05), though not by radioimmunoassay insulin (87 and 144 pmol/1,p = 0.12), respectively. Individual immunoradiometric assay insulin responses to glucose expressed in terms of obesity were subnormal in nine of ten diabetic subjects. Radioimmunoassay insulin and C-peptide gave less complete discrimination ( subnormal responses in six of ten and eight of ten, respectively). Thus, raised proinsulin and proinsulin:total insulin ratio are not necessarily a feature of mild diet-treated Type 2 diabetic patients with subnormal insulin responses to glucose.     

Short Administration of Metformin Improves Insulin Sensitivity in Android Obese Subjects with Impaired Glucose Tolerance

In a double-blind, randomized, cross-over study, the metabolic effects of a short treatment with metformin (2 times 850 mg day^?1 for 2 days and 850 mg 1 h before evaluation) were compared to those of placebo in 15 obese subjects (BMI: 33.2 ± 0.9 kg m^?2), with abdominal distribution of adipose tissue and impaired glucose tolerance. An intravenous glucose tolerance test (0.3 g glucose kg^?1) was performed after each period of treatment. Areas under the curve (AUC_{0–180 min}) were calculated for plasma glucose, insulin, and C-peptide levels. Glucose tolerance was estimated by the coefficient of glucose assimilation (K_G). Insulin sensitivity (S_I) and glucose effectiveness (S_G) indices were calculated using Bergman's minimal model. Insulin secretion rate (ISR) was determined by deconvolution of plasma C-peptide levels and insulin metabolic clearance rate (MCR) was estimated by dividing AUC ISR by AUC insulin. Fasting plasma insulin levels were reduced after metformin (89.3 ± 15.9 vs 112.4 ± 24.3 pmol I^?1; p = 0.04). AUC glucose, K_G and S_G were similar in both tests. However, AUC insulin was reduced (39.7 ± 6.5 vs 51.8 ± 10.4 nmol min I^?1; p = 0.02), while S_I (6.98 ± 1.14 vs 4.61 ± 0.42 10^?5 min^?1 pmol^?1 I; p = 0.03) and insulin MCR (715 ± 116 vs 617 ± 94 ml min^?1 m^?2; p = 0.03) were increased after metformin. The demonstration that metformin rapidly improves insulin sensitivity should encourage further research to evaluate the long-term effects of metformin in android obese subjects with impaired oral glucose tolerance.     

Increased plasma leptin in gestational diabetes

Aims/hypothesis. Insulin resistance as well as marked changes in body weight and energy metabolism are associated with pregnancy. Its impact on plasma leptin is not known and was determined in this longitudinal study in both diabetic and normal pregnancy. Methods. At 28 gestational weeks plasma concentrations of leptin and B-cell hormones were measured at fasting and after an oral glucose load (OGTT:75 g) in women with gestational diabetes and pregnant women with normal glucose tolerance and compared with women who were not pregnant (C). Results. Plasma leptin (ng/ml) was higher (p < 0.001) in women with gestational diabetes (24.9 ± 1.6) than in women with normal glucose tolerance (18.2 ± 1.5) and increased in both groups when compared with the non-pregnant women (8.2 ± 1.3; p < 0.0005). No change in plasma leptin concentrations was induced by OGTT in any group. Basal insulin release was higher (p < 0.05) in women with gestational diabetes compared with the pregnant women with normal glucose tolerance. Marked insulin resistance was confirmed by a 20 % lower (p < 0.05) insulin sensitivity in subgroup analysis and a decrease of almost 40 % in fasting glucose/insulin ratio (p < 0.005) in women with gestational diabetes. Leptin correlated in women with gestational diabetes with basal plasma concentrations of glucose (p < 0.02), insulin (p < 0.004) and proinsulin (p < 0.01) as well as with BMI (p < 0.001) and overall pregnancy induced maternal weight gain (p < 0.009). With normalisation of blood glucose 8 weeks after delivery in women with gestational diabetes their plasma leptin decreased (p < 0.0005) to 17.3 ± 1.9 ng/ml but did not completely normalize (p < 0.05 vs non-pregnant women). Conclusion/interpretation. Our data show that women with gestational diabetes without any change in plasma leptin upon oral glucose loading have increased plasma leptin concentrations during and after pregnancy, a clear association of plasma leptin with the respective concentration of glucose and insulin resistance as well as with changes in body weight, and a failure to normalize spontaneously BMI to the same extent as pregnant women with normal glucose tolerance when compared with matched control subjects. [Diabetologia (2001) 44: 164–172] Received: 11 July 2000 and in revised form: 10 October 2000     

Forearm Substrate Exchange during Hyperinsulinaemic Hypoglycaemia in Normal Man

To assess muscle substrate exchange during hypoglycaemia, 8 healthy young male subjects were studied twice during 2 h of hyperinsulinaemic euglycaemia followed by 4 h of (1) hypoglycaemia (plasma glucose < 2.8 mmol l^?1), and (2) euglycaemia. Insulin was infused at a rate of 1.5 mU kg^?1 min^?1 throughout. When compared to euglycaemia, hypoglycaemia was associated with: (1) increment in circulating glucagon (65 ± 8 vs 23 ± 4 ng l^?1, p < 0.05), growth hormone (19.9 ± 3.6 vs 2.6 ± 1.3 μg l^?1, p < 0.05), adrenaline (410 ± 88 vs 126 ± 32 ng l^?1, p < 0.05) and increased suppression of C-peptide (0.5 ± 0.1 vs 1.0 ± 0.1 μg l^?1, p < 0.05) along with a modest lowering of insulin (103 ± 10 vs 130 ± 13 mU l^?1, p < 0.05); (b) decrease in plasma glucose level (3.0 ± 0.07 vs 5.0 ± 0.12 mmol l^?1 p < 0.05), forearm glucose uptake (0.21 ± 0.09 vs 1.21 ± 0.21 mmol l^?1, p < 0.05) and requirement for exogenous glucose (5.6 ± 1.1 vs 13.2 ± 0.9 mg kg^?1 min^?1 p < 0.005) together with an impaired suppression of isotopically determined endogenous glucose production (0.34 ± 0.5 vs ?2.3 ± 0.3 mg kg^?1 min^?1, p < 0.05); (3) exaggerated increase in blood lactate (1680 ± 171 vs 1315 ± 108 μmol l^?1, p < 0.05) and a decrease in alanine (215 ± 18 vs 262 ± 19 μmol l^?1, p < 0.05). Forearm release of lactate (130 ± 43 vs 12 ± 31 μmol l^?1, p = 0.09) tended to be increased, whereas alanine balance (18 ± 6 vs 17 ± 5 μmol l^?1) was unchanged. (4) Total forearm blood flow increased similarly during both studies (4.4 ± 0.6 vs 4.2 ± 0.5 ml 100 ml^?1 min^?1). These data suggest that the human forearm is not a major site for glucose uptake nor for lactate production during protracted hypoglycaemia; the fact that forearm glucose uptake is reduced sixfold during hypoglycaemia further suggests that restriction of glucose uptake in muscles plays a frontline role in the defence against hypoglycaemia.     

Increased insulin secretory capacity but decreased insulin sensitivity after correction of iron overload by phlebotomy in hereditary haemochromatosis

Aims/hypothesis We recently demonstrated that humans with hereditary haemochromatosis have decreased insulin secretory capacity with a compensatory increase in insulin sensitivity. We therefore determined how these measures change after correction of tissue iron overload.Subjects and methods Five non-diabetic subjects who had been studied previously at the time of initial diagnosis by means of the OGTT and frequently sampled intravenous glucose tolerance tests (FSIVGTT) underwent phlebotomy to normalise their serum ferritin. After normalisation of ferritin they were studied again (33±4 months after the initial studies) by OGTT and FSIVGTT.Results Normalisation of tissue iron stores resulted in an average 1.8-fold increase in the integrated area under the insulin curve during OGTT (p<0.0001), but no significant change in the area under the glucose curve (10% decrease, p=0.32). After phlebotomy, there was a 2.2-fold increase in insulin secretory capacity as determined by FSIVGTT (acute insulin response to glucose [AIRg], p<0.02) but a concomitant 70% fall in insulin sensitivity (Si, p<0.05). The disposition index (AIRg×Si) was unchanged (5% increase, p=0.90). BMI and fasting glucose were unchanged. At the time of diagnosis of haemochromatosis, four of the subjects had IGT. After normalisation of ferritin, two achieved NGT and two remained with IGT, despite 2.5- and 3.7-fold increases in insulin secretory capacity.Conclusions/interpretation Insulin secretory capacity improves after normalisation of iron stores in subjects with hereditary haemochromatosis. Glucose tolerance status improves incompletely because of decreased insulin sensitivity after phlebotomy. We conclude that tissue iron levels are an important determinant of insulin secretion and insulin action.     

Insulin sensitivity in alcoholics in a withdrawal state

Abstract. Insulin sensitivity in non-diabetic alcoholics in a withdrawal state was investigated using a euglycaemic clamp technique on two occasions with an interval of 1 week. Insulin was infused at a rate of 40 mU m^?2 min^?1 (n = 9) and 20 mU m^?2 min^?1 (n = 9). Hepatic glucose production was estimated with tritiated glucose in six subjects. The fasting glucose level at the first examination, 5.1 ± 0.2 mmol l^?1 exceeded that found at the second examination, 4.7 ± 0.1 mmol l^?1 (P < 0.05), although the C-peptide concentration was higher at the first examination (2.7 ± 0.3 vs. 1.6 ± 0.2 ng ml^?1: P < 0.001). Both glucose uptake (5.0 ± 0.6 vs 6.2 ± 0.7 mg kg^?1 min^?1: P < 0.05) and tissue sensitivity (M/I; 0.08 ± 0.02 vs. 0.1 ± 0.02 mg kg^?1 min^?1/mU l^?1; P < 0.05) increased between the first and second euglycaemic clamp (40 mU m^?2 min^?1). At the low insulin infusion rate (20 mU m^?2 min^?1), the tissue sensitivity to insulin increased (0.09 ± 0.01 vs. 0.13 ± 0.02 mg kg^?1 min^?1/mU l^?1; P < 0.05). Hepatic glucose production did not change during the examination period (2.2 ± 0.2 vs. 2.3 ± 0.1 mg kg^?1 min^?1), neither was there a change in the suppression of hepatic glucose output during hyperinsulinaemia (40 mU m^?2 min^?1). Our findings indicate that, in non-diabetic alcoholics, insulin sensitivity in peripheral tissues is decreased during the early part of a withdrawal period.     

1-Hour plasma glucose in obese youth

Adults with normal glucose tolerance (NGT) but exaggerated plasma glucose excursion at 1?h (1HPG) following the oral glucose tolerance test (OGTT) have significantly higher risk of developing impaired glucose tolerance (IGT) or diabetes. Aim of the study will be to characterize the metabolic phenotype of NGT obese youth according to values of 1HPG. To accomplish this aim, obese patients (N?=?1,454; 761 men; 79 IGT; BMI z-score 2.56?±?0.16 SDS; age 11?±?0.7?years) from two data sets were analyzed. In all patients, empirical parameters of insulin metabolism were calculated in fasting condition and following an OGTT (1.75?mg of glucose per kilogram/body weight). Receiver-operating characteristic (ROC) analysis was performed in the first group (training set, N?=?920) to establish the cutoff value of 1HPG best identifying IGT. The second set (validation set, N?=?534) served to verify the goodness of the model and the identified cutoff values. 1HPG????132.5?mg/dl identified IGT with 80.8% sensitivity and 74.3% specificity in the training set (AUC 0.855, 95% CI 0.808?C0.902, p?<?0.0001), and 70.3% sensitivity and 80% specificity in the validation set (AUC 0.81, 95% CI 0.713?C0.907, p?<?0.0001), respectively. NGT patients with 1HPG????132.5?mg/dl had a metabolic phenotype (triglycerides, insulin action, and secretion) that was in between those of NGT patients with 1HPG below the threshold and IGT patients (p?<?0.0001 for all the comparisons). 1HPG????132.5?mg/dl seems to be associated with increased metabolic risk in obese youth, identifying patients with lower insulin sensitivity, early secretion, and higher total insulin secretion than in obese mates with lower 1HPG.     

Serum proinsulin levels at fasting and after oral glucose load in patients with Type 2 (non-insulin-dependent) diabetes mellitus

Summary A simple and sensitive human proinsulin radioimmunoassay system was developed using guinea pig antiproinsulin serum, which cross-reacted neither with human insulin nor C-peptide. The recognition site of the antiserum seems to be located near the junction between the B chain and C-peptide. With this assay system, we studied the serum proinsulin concentration at fasting and after an oral 100 g glucose load in 25 healthy subjects, 21 subjects with impaired glucose tolerance and 40 patients with Type 2 (non-insulin-dependent) diabetes mellitus. At fasting, serum proinsulin was 5.8±3.3 pmol/l in normal subjects as compared to 9.5±6.9 pmol/l (p<0.05) in subjects with impaired glucose tolerance and 12.6±7.5 pmol/l (p<0.001) in diabetic patients. The molar ratio of proinsulin to insulin was also increased in subjects with impaired glucose tolerance or diabetes compared to control subjects. After a 100 g oral glucose load, serum proinsulin increased more slowly than insulin. The proinsulin response after an oral glucose load was augmented in subjects with impaired glucose tolerance and diabetes, while the insulin response decreased with the elevation of fasting plasma glucose. Diabetic patients with high fasting plasma glucose had a very poor insulin response, but the proinsulin response was similar to control subjects. There was a linear correlation between summed proinsulin values and summed insulin values, but the slope of the regression line was steeper in diabetic patients than in control subjects. There was a relative increase in serum proinsulin both in subjects with impaired glucose tolerance and diabetic patients. We suggest that B cells may release ‘immature’ granules richer in proinsulin content as well as mature granules in the over-stimulated state.     

Impaired early- but not late-phase insulin secretion in subjects with impaired fasting glucose

Subjects with impaired fasting glucose (IFG) are at increased risk for type 2 diabetes. We recently demonstrated that IFG subjects have increased hepatic insulin resistance with normal insulin sensitivity in skeletal muscle. In this study, we quantitated the insulin secretion rate from deconvolution analysis of the plasma C-peptide concentration during an oral glucose tolerance test (OGTT) and compared the results in IFG subjects with those in subjects with impaired glucose tolerance (IGT) and normal glucose tolerance (NGT). One hundred and one NGT subjects, 64 subjects with isolated IGT, 24 subjects with isolated IFG, and 48 subjects with combined (IFG + IGT) glucose intolerance (CGI) received an OGTT. Plasma glucose, insulin, and C-peptide concentrations were measured before and every 15 min after glucose ingestion. Insulin secretion rate (ISR) was determined by deconvolution of plasma C-peptide concentration. Inverse of the Matsuda index of whole body insulin sensitivity was used as a measure of insulin resistance; 56 subjects also received a euglycemic hyperinsulinemic clamp. The insulin secretion/insulin resistance (disposition) index was calculated as the ratio between incremental area under the ISR curve (∆ISR[AUC]) to incremental area under the glucose curve (∆G[AUC]) factored by the severity of insulin resistance (measured by Matsuda index during OGTT or glucose disposal during insulin clamp). Compared to NGT, the insulin secretion/insulin resistance index during first 30 min of OGTT was reduced by 47, 49, and 74% in IFG, IGT, and CGI, respectively (all < 0.0001). The insulin secretion/insulin resistance index during the second hour (60–120 min) of the OGTT in subjects with IFG was similar to that in NGT (0.79 ± 0.6 vs. 0.72 ± 0.5, respectively, P = NS), but was profoundly reduced in subjects with IGT and CGI (0.31 ± 0.2 and 0.19 ± 0.11, respectively; P < 0.0001 vs. both NGT and IFG). Early-phase insulin secretion is impaired in both IFG and IGT, while the late-phase insulin secretion is impaired only in subjects with IGT.