Abnormalities of islet B-cell function, insulin action, and fat distribution in women with histories of gestational diabetes: relationship to obesity

Metabolic phenotyping by treatment modality in obese women with gestational diabetes suggests diverse pathophysiology: An exploratory study

Background and purpose

Excess insulin resistance is considered the predominant pathophysiological mechanism in obese women who develop gestational diabetes (GDM). We hypothesised that obese women requiring differing treatment modalities for GDM may have diverse underlying metabolic pathways.

Methods

In this secondary analysis of the UK pregnancies Better Eating and Activity Trial (UPBEAT) we studied women from the control arm with complete biochemical data at three gestational time points; at 15–18⁺⁶ and 27–28⁺⁶ weeks (before treatment), and 34–36⁺⁰ weeks (after treatment). A total of 89 analytes were measured (plasma/serum) using a targeted nuclear magnetic resonance (NMR) platform and conventional assays. We used linear regression with appropriate adjustment to model metabolite concentration, stratified by treatment group.

Main findings

300 women (median BMI 35kg/m²; inter quartile range 32.8–38.2) were studied. 71 developed GDM; 28 received dietary treatment only, 20 metformin, and 23 received insulin. Prior to the initiation of treatment, multiple metabolites differed (p<0.05) between the diet and insulin-treated groups, especially very large density lipoprotein (VLDL) and high density lipoprotein (HDL) subclasses and constituents, with some differences maintained at 34–36 weeks’ gestation despite treatment. Gestational lipid profiles of the diet treatment group were indicative of a lower insulin resistance profile, when compared to both insulin-treated women and those without GDM. At 28 weeks’ the diet treatment group had lower plasma fasting glucose and insulin than women treated with insulin, yet similar to those without GDM, consistent with a glycaemic mechanism independent of insulin resistance.

Conclusions/Interpretation

This exploratory study suggests that GDM pathophysiological processes may differ amongst obese women who require different treatment modalities to achieve glucose control and can be revealed using metabolic profiling.

Pancreatic Islet Responses to Metabolic Trauma

Carbohydrate, lipid, and protein metabolism are largely controlled by the interplay of various hormones, which includes those secreted by the pancreatic islets of Langerhans. While typically representing only 1% to 2% of the total pancreatic mass, the islets have a remarkable ability to adapt to disparate situations demanding a change in hormone release, such as peripheral insulin resistance. There are many different routes to the onset of insulin resistance, including obesity, lipodystrophy, glucocorticoid excess, and the chronic usage of atypical antipsychotic drugs. All of these situations are coupled to an increase in pancreatic islet size, often with a corresponding increase in insulin production. These adaptive responses within the islets are ultimately intended to maintain glycemic control and to promote macronutrient homeostasis during times of stress. Herein, we review the consequences of specific metabolic trauma that lead to insulin resistance and the corresponding adaptive alterations within the pancreatic islets.

Improvements in insulin sensitivity after aerobic exercise and weight loss in older women with a history of gestational diabetes and type 2 diabetes mellitus

PURPOSE

To determine whether a hypocaloric diet alone (WL) or with exercise training (AEX + WL) is effective in improving body composition, fitness, glucose utilization and CVD risk factors in sedentary women with a history of gestational diabetes (GDM) and with type 2 diabetes (T2DM).

MATERIALS AND METHODS

Longitudinal clinical investigation of 25 overweight/obese (BMI: 32 ± 1 kg/m(2)) women (59 ± 1 yrs) with a GDM history (n = 20) or T2DM (n = 5). Women completed 6 months WL (n = 10) or AEX+WL (n = 15) with VO2max, body composition, and glucose tolerance testing. Insulin sensitivity was measured during the last 30 min of 2 h hyperinsulinemic-euglycemic clamps (40 mU·m(-2.)min(-1)) before and after interventions.

RESULTS

Body weight decreased ~7% after WL and AEX+WL (p < 0.001), with an 11-12% decrease in fat mass (p < 0.0001). Visceral fat and subcutaneous abdominal fat decreased 27 and 10% after WL (p < 0.01) and 14 and 11% after AEX + WL (p < 0.05). VO2max increased 16% after AEX + WL (p < 0.001) and did not change after WL. Glucose AUC decreased 14 and 13% after WL (p < 0.05) and AEX + WL (p < 0.01) with a 42% decrease in insulin AUC after AEX + WL (p < 0.01). Glucose utilization increased 25% (p = 0.05) with AEX + WL and 7% with WL.

CONCLUSIONS

A six-month aerobic exercise program combined with moderate weight loss reduces body weight, visceral and subcutaneous abdominal fat, and improves insulin sensitivity in older women who had previously been diagnosed with GDM and those with T2DM. These findings should encourage women with a history of GDM to engage in an active lifestyle and reduce caloric intake to lower the risk for the development of T2DM.

Skeletal Muscle CAP Expression Increases after Dietary Restriction and Aerobic Training in Women with a History of Gestational Diabetes

The purpose is to determine the effects of 6 months caloric restriction and aerobic training (3x/wk) (CR+AEX) on c-CBL associated protein (CAP) gene expression in women with a history of GDM. CAP is involved in cell signaling and protein ubiquitination, and is linked to the development of insulin resistance. Obese (BMI=32 ± 1 kg/m², % fat=46 ± 2, X ± SEM), sedentary (VO2 max=21.2 ± 1.2 ml/kg/min), women aged 52 ± 2 years participated in 6 months D+WL (n=10) with body composition, fitness (VO2 max), and glucose tolerance testing. Insulin sensitivity was assessed during the last 30 min of 2-hour hyperinsulinemic-euglycemic clamps (40 mU.m^-2.min^-1) pre and post interventions. Vastus lateralis skeletal muscle biopsies (n=7) were conducted and CAP, GLUT4 and glycogen synthase (GS) gene expression measured by RT-PCR. No change in FFM by DXA was observed, but body weight decreased 8% with losses of total body fat mass (P<0.05) and a 10% increase in VO2 max (P<0.01). Glucose and insulin areas under the curve by OGTT decreased (P<0.05). Glucose utilization during the clamp increased 27% (23.1 ± 3.8 vs. 29.4 ± 3.6 umol.kg.min^-1, P<0.05). Vastus lateralis skeletal muscle CAP expression increased 21% (P<0.05) but GLUT4 did not. Results suggest that changes in CAP could be involved in the improvement in glucose metabolism with caloric restriction and aerobic training in women with a history of gestational diabetes.

Accelerated metabolic susceptibility to type 2 diabetes in older women with a history of gestational diabetes

The purpose of this study is to compare central obesity, insulin sensitivity, and cardiovascular disease risk factors between premenopausal and postmenopausal women with a history of gestational diabetes mellitus (GDM), controls, and women with type 2 diabetes (T2DM). Subjects were 73 overweight/obese and sedentary women who had a history of GDM (n=31) and were either premenopausal (n=11, 44±1 years, X±s.e.m.), postmenopausal (n=20, 58±1 years), or without a history of GDM as healthy postmenopausal controls (n=27, 57±1 years) or postmenopausal with T2DM (n=16, 59±1 years). The premenopausal GDM women had higher maximal oxygen uptake and lower visceral fat than the other three groups (P<0.05). BMI, %body fat, subcutaneous abdominal fat, and intramuscular fat did not differ significantly among the four groups. Glucose utilization (M, 3 h 40 mU/m(2) per min hyperinsulinemic-euglycemic clamps) was 27% higher (P=0.05) in pre- than postmenopausal GDM and was not different between premenopausal GDM and postmenopausal controls. M was 28% lower (P=0.06) in postmenopausal GDM than controls and was not significantly different between postmenopausal GDM and T2DM groups. Thus, despite being younger and more physically fit, premenopausal women with prior GDM display similar central obesity, glucose, and metabolic profiles as postmenopausal controls. Postmenopausal women with prior GDM are more insulin resistant than controls of similar age, adiposity, and fitness levels and display comparable glucose utilization rates as similar as women with T2DM suggesting that a prior history of GDM may be an early manifestation of increased risk of later T2DM.

Women with normal glucose tolerance and a history of gestational diabetes show significant impairment of β-cell function at normal insulin sensitivity

OBJECTIVE

Although the nature of gestational diabetes mellitus (GDM) remains unclear, the condition is thought to be related primarily to insulin resistance, overweight and obesity. Most studies include women with a history of GDM and later carbohydrate metabolism abnormalities, while reports of women with previous GDM and subsequent normoglycaemia are scarce. The aim of this study was to assess insulin resistance and β-cell function in normoglycaemic women with a history of GDM.

MATERIALS AND METHODS

The study group included 199 women, aged 38.4±6.6 years, diagnosed with GDM within the last 5-12 years [GDM(+)] and a control group of 50 comparable women in whom GDM was excluded [GDM(-)], according to WHO criteria. Blood glucose and insulin levels were measured at the beginning (fasting) and at 60 and 120min of oral glucose tolerance tests. Indices of insulin resistance (HOMA-IR), insulin sensitivity (HOMA-S%) and β-cell function (HOMA-B%) were calculated.

RESULTS

Normoglycaemia was observed in 57% of GDM(+) and 88% of GDM(-) women (P=0.0003). Diabetes was diagnosed in 13 (6.5%) GDM(+) women and in none of the GDM(-) women. Comparison of 113 normoglycaemic GDM(+) and 44 normoglycaemic GDM(-) women revealed significantly impaired β-cell function (HOMA-B%: 131.1±51.1 vs 144.7±47.1, respectively; P=0.038) with similar normal body mass index (BMI) and no differences in HOMA-IR and HOMA-S%.

CONCLUSION

In this study, more than half of the GDM(+) women were presented with normal glucose tolerance. However, despite normoglycaemia, women with a history of GDM were characterized by significantly impaired insulin secretion, but no signs of increased insulin resistance.

Value of the intravenous and oral glucose tolerance tests for detecting subtle impairments in insulin sensitivity and beta-cell function in former gestational diabetes

OBJECTIVE

Women with former gestational diabetes mellitus (fGDM) often show defects in both insulin sensitivity and beta-cell function but it is not clear which defect plays the major role or which appears first. This might be because fGDM women are often studied as a unique group and not divided according to their glucose tolerance. Different findings might also be the result of using different tests. Our aim was to study insulin sensitivity and beta-cell function with two independent glucose tolerance tests in fGDM women divided according to their glucose tolerance.

DESIGN AND PATIENTS

A total of 108 fGDM women divided into normal glucose tolerance (IGT; N = 82), impaired glucose metabolism (IGM; N = 20) and overt type 2 diabetes (T2DM; N = 6) groups, and 38 healthy control women (CNT) underwent intravenous (IVGTT) and oral glucose tolerance tests (OGTT). Measurements Insulin sensitivity and beta-cell function were assessed by both the IVGTT and the OGTT.

RESULTS

Both tests revealed impaired insulin sensitivity in the normotolerant group compared to controls (IVGTT: 4.2 +/- 0.3 vs. 5.4 +/- 0.4 10(-4) min(-1) (microU/ml)(-1); OGTT: 440 +/- 7 vs. 472 +/- 9 ml min(-1) m(-2)). Conversely, no difference was found in beta-cell function from the IVGTT. However, some parameters of beta-cell function by OGTT modelling analysis were found to be impaired: glucose sensitivity (106 +/- 5 vs. 124 +/- 7 pmol min(-1) m(-2) mm(-1), P = 0.0407) and insulin secretion at 5 mm glucose (168 +/- 9 vs. 206 +/- 10 pmol min(-1) m(-2), P = 0.003).

CONCLUSIONS

Both insulin sensitivity and beta-cell function are impaired in normotolerant fGDM but the subtle defect in beta-cell function is disclosed only by OGTT modelling analysis.

Postpartum adiponectin concentration, insulin resistance and metabolic abnormalities among women with pregnancy-induced disturbances

The authors compared postpartum adiponectin levels among women with prior pregnancy-induced disturbances and assessed their association with homeostasis model assessment for insulin resistance (HOMA-IR), the metabolic syndrome (MS), and the Framingham risk score (FRS). Women delivering in 1998 through 2001 and who had gestational diabetes mellitus (n=22), gestational hypertension (n=32), or preeclampsia (n=34) were examined 1 to 2 years after delivery and were grouped-matched to controls (n=29) by age and prepregnancy body mass index. HOMA-IR was increased, adiponectin values were decreased, and there was a higher MS prevalence in women with prior gestational diabetes mellitus (all P<.05). Adiponectin levels were inversely related to HOMA-IR (r=-0.45; P<.0001) and FRS (r=-0.25; P=.007), and a significant trend for decreasing adiponectin values with increased number of MS components was noted (P trend <.0001). Adiponectin concentration remained a significant correlate of FRS and MS irrespective of pregnancy history; a concentration <10.5 microg/mL provided the optimal cutoff to distinguish those with or without MS. Thus, a lower postpartum adiponectin concentration identifies women at increased cardiovascular risk regardless of pregnancy history.

Visceral fatness and insulin sensitivity in women with a previous history of gestational diabetes mellitus

OBJECTIVE

The purpose of this study was to investigate the insulin sensitivity and visceral fatness in women with previous gestational diabetes mellitus (GDM), who are prone to develop type 2 diabetes.

RESEARCH DESIGN AND METHODS

A 75-g oral glucose tolerance test (OGTT) performed 1 year postpartum identified 21 GAD(-) women with previous GDM and impaired glucose tolerance (GDM-IGT). Sixty age- and BMI-matched women with normal glucose tolerance (GDM-NGT) were selected by 1:3 matching to the GDM-IGT group. Another 18 women with normal glucose metabolism during a previous pregnancy and no family history of diabetes were recruited as the normal control group. Age and BMI matching was performed using a range of +/-1.0 years and +/-1.0 kg/m(2), respectively. Total body fat was measured by tetrapolar bioelectrical impedance, and visceral fat was determined using a single cut of a computed tomography scan. Insulin sensitivity was determined by the minimal model technique using the frequently sampled intravenous glucose tolerance test.

RESULTS

One year postpartum, visceral fat was greater in the GDM-IGT group than in the age- and BMI-matched GDM-NGT or normal control groups. The insulin sensitivity index was lower in the GDM-IGT group than in the GDM-NGT or normal control groups. beta-Cell function, as measured by the acute insulin response to glucose, was also lower in GDM-IGT.

CONCLUSIONS

High body fat content, especially visceral fat content, and a low insulin response to glucose seem to contribute simultaneously to the development of impaired glucose metabolism in Korean women with previous GDM.

Sustained endogenous glucose production, diminished lipolysis and non-esterified fatty acid appearance and oxidation in non-obese women at high risk of type 2 diabetes

OBJECTIVE

To evaluate early defects in glucose production, lipolysis and fatty acid oxidation in non-obese, normally glucose tolerant women, who are nevertheless at risk of type 2 diabetes.

METHODS

Ten women with previous gestational diabetes (pGDM) and ten controls were studied in two 4 h infusions of stable isotopes 6,6-(2)H(2)-glucose, 1-(13)C-palmitate, and 1,1,2,3,3-(2)H(5)-glycerol with and without infusion of adrenaline. Fatty acid oxidation was quantified using indirect calorimetry and (13)CO(2) measurements. Insulin sensitivity was evaluated using the short insulin tolerance test.

RESULTS

The pGDM and control women were non-obese and carefully matched for body mass index and fat mass. Whole body insulin sensitivity and basal insulin concentrations did not differ significantly but basal glucose concentrations were increased in women with pGDM. During a 0.9% saline infusion, glucose appearance was not significantly different at the first (90-120 min) and second (210-240 min) steady states. However, glucose appearance decreased in controls but was maintained in the pGDM women (-0.33 +/- 0.02 vs -0.03 +/- 0.08 mg/kg per min; P = 0.004). Basal glycerol appearance (0.27 +/- 0.02 vs 0.38 +/- 0.03 mg/kg per min; P = 0.02), palmitate appearance (0.74 +/- 0.09 vs 1.05 +/- 0.09 mg/kg per min; P = 0.03) and palmitate oxidation (0.07 +/- 0.01 vs 0.10 +/- 0.01 mg/kg per min; P = 0.03) were lower in the pGDM women. During the adrenaline infusion, changes in glucose, glycerol and palmitate concentrations and kinetics were similar in both groups.

CONCLUSIONS

Sustained glucose production during fasting is an early abnormality in non-obese subjects at risk of type 2 diabetes. Lipolysis and non-esterified fatty acid appearance and oxidation are diminished, suggesting an increased tendency to store fat. The observations are not readily attributable to differences in insulin or catecholamine sensitivity.

Nutrient intake of women with and without gestational diabetes with a specific focus on fatty acids

OBJECTIVE

Diet therapy is the cornerstone for the management of gestational diabetes mellitus (GDM). Women with GDM are commonly given dietary advice that broadly focuses on a reduction of total energy and fat consumption. We compared nutrient intake and specifically fatty acids of women with GDM who had received individualized nutritional counseling with those of non-diabetic women who did not.

METHOD

Women with GDM (n=44) and healthy pregnant women (n=44) with uncomplicated singleton pregnancies were recruited during the third trimester. Women with GDM were given consultation on diet, health, and macronutrient content of foods commonly consumed by the individual. The non-diabetic group did not receive any dietary advice. Both groups were asked to keep a detailed record of all of foods and fluid consumed over a 4-d period.

RESULTS

After dietary counseling, the GDM group had lower intakes of energy (P<0.05), refined sugar (P<0.0001), total and saturated fats (P<0.0001), and monounsaturated (P<0.01) and trans (P<0.0001) fatty acids and higher levels of docosahexaenoic acid and fiber (P<0.05) compared with the non-diabetic group.

CONCLUSIONS

Individualized dietary advice was associated with a lower consumption of the target nutrients in women with GDM. Another benefit of the advice was a slight increase in intake of eicosapentaenoic and docosahexaenoic acids, although consumption of omega-3 fatty acids by both groups was well below the recommendations for pregnancy. There is evidence that docosahexaenoic acid modulates insulin resistance and that it is vital for neurovisual development. We suggest that dietary management for women with GDM should foster the current recommendations for essential fatty acids in pregnancy.

Impaired beta-cell function in lean normotolerant former gestational diabetic women

BACKGROUND

Former gestational diabetes (fGDM) constitutes a risk condition for the development of Type 2 diabetes. Former gestational diabetes is often characterized by obesity and hyperglycaemia, which may be concomitant and independent risk factors.

MATERIALS AND METHODS

To assess insulin sensitivity and beta-cell function in fGDM uncomplicated by obesity and hyperglycaemia, we studied 24 lean fGDM women and 23 control women matched for age (30.7 +/- 0.7 years, whole cohort), body mass index (22.2 +/- 0.3 kg m(-2)), and indistinguishable for plasma glucose both at fasting and at 120 min. Several insulin sensitivity and beta-cell function indices were computed: homeostasis model assessment insulin resistance index (HOMA-R), insulin sensitivity index derived from an oral glucose tolerance test (OGIS), insulinogenic index, other empirical indices of insulin secretion and beta-cell function, and indices obtained using a beta-cell model.

RESULTS

Though the majority of indices, and in particular insulin sensitivity (HOMA-R: 1.35 +/- 0.13 vs. 1.65 +/- 0.14; OGIS: 492.7 +/- 6.3 vs. 496.4 +/- 9.4 mL min(-1) m(-2)), were not significantly different in the two groups, the beta-cell glucose sensitivity obtained by modelling analysis was lower in fGDM (108 +/- 14 vs. 165 +/- 22 pmol min(-1) m(-2) mM(-1), P = 0.031).

CONCLUSIONS

Impairment of beta-cell glucose sensitivity may be an intrinsic risk factor in fGDM independently of obesity and hyperglycaemia. Furthermore, we have shown that modelling analysis, in contrast to the empirical parameters, may be able to detect early beta-cell alterations in fGDM women.

Gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is defined as glucose intolerance of various degrees that is first detected during pregnancy. GDM is detected through the screening of pregnant women for clinical risk factors and, among at-risk women, testing for abnormal glucose tolerance that is usually, but not invariably, mild and asymptomatic. GDM appears to result from the same broad spectrum of physiological and genetic abnormalities that characterize diabetes outside of pregnancy. Indeed, women with GDM are at high risk for having or developing diabetes when they are not pregnant. Thus, GDM provides a unique opportunity to study the early pathogenesis of diabetes and to develop interventions to prevent the disease.

Gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is defined as glucose intolerance of various degrees that is first detected during pregnancy. GDM is detected through the screening of pregnant women for clinical risk factors and, among at-risk women, testing for abnormal glucose tolerance that is usually, but not invariably, mild and asymptomatic. GDM appears to result from the same broad spectrum of physiological and genetic abnormalities that characterize diabetes outside of pregnancy. Indeed, women with GDM are at high risk for having or developing diabetes when they are not pregnant. Thus, GDM provides a unique opportunity to study the early pathogenesis of diabetes and to develop interventions to prevent the disease.

Rationale for prevention and treatment of glucose-mediated macrosomia: a protocol for gestational diabetes

OBJECTIVE

To formulate a rationale for preventing and treating hyperglycemia during pregnancy and the concomitant risk of macrosomia.

METHODS

We reviewed pertinent studies in the literature and personal experience with patients who had gestational diabetes. In addition, dietary and exercise interventions in the management of such patients were assessed.

RESULTS

During pregnancy, sequential hormonal increases occur to provide glucose substrate to the fetus. When a pregnant woman has a limited insulin secretory capacity and cannot produce enough insulin to compensate for the effect of diabetogenic hormones, gestational diabetes occurs (usually during the second trimester). Maternal hyperglycemia reportedly increases fetal secretion of insulin, and fetal hyperinsulinemia may predispose the fetus to macrosomia. Thus, metabolic abnormalities associated with diabetes during pregnancy result in long-term effects on the offspring, including insulin resistance, obesity, and diabetes, which in turn may contribute to transmission of risk for development of the same problems in subsequent generations. Insulin therapy, dietary measures, and exercise have helped to achieve euglycemia in patients with gestational diabetes.

CONCLUSION

Universal screening for gestational diabetes is optimally performed at 26 weeks of gestation. Treatment of diagnosed cases, by insulin, diet, and exercise regimens, will decrease the occurrence of glucose-related macrosomia, improve the outcome of the pregnancy, and reduce the risks for obesity, hypertension, and diabetes in future progeny.

Insulin resistance and beta-cell dysfunction in normoglycaemic European women with a history of gestational diabetes

OBJECTIVE

Women with previous gestational diabetes (GDM) are at increased risk of subsequent type 2 diabetes. To characterize early metabolic abnormalities associated with this increased risk, we studied normoglycaemic women with a history of GDM.

PATIENTS AND MEASUREMENTS

We performed an insulin-modified, frequently sampled intravenous glucose tolerance test (FSIVGTT) in 34 normoglycaemic European women with previous GDM and 44 European control women, deriving measures of insulin sensitivity, glucose effectiveness, glucose disappearance rate and acute insulin response to glucose.

RESULTS

Post-GDM women were more obese than controls [body mass index (BMI), geometric mean (95% confidence interval); 25.3 kg/m2 (23.8-27.1 kg/m2) vs. 23.1 kg/m2 (21.9-24.3 kg/m2), P = 0.03]. Evidence of insulin resistance was provided by their lower insulin sensitivity as measured by FSIVGTT [0.6 x 10-4/min/pmol/l (0.3-1.2 x 10-4/min/pmol/l) vs. 1.5 x 10-4/min/pmol/l (1.2-1.8 x 10-4/min/pmol/l), P = 0.01] and by homeostatic model assessment [72% (49-107%) vs. 153% (113-206%), P = 0.004]; and by their higher fasting triglycerides [1.0 mmol/l (0.7-1.5 mmol/l) vs. 0.7 mmol/l (0.6-0.8 mmol/l), P = 0.001]. Though there was no difference between groups in fasting NEFA levels, acute NEFA suppression was diminished in the post-GDM group (P = 0.01). Concomitant beta-cell dysfunction in the post-GDM women was revealed by their lower disposition index [0.05/min (0.02-0.10/min) vs. 0.11/min (0.09-0.14/min), P = 0.02] compared to controls. The differences in insulin sensitivity, but not those of beta-cell function, were partly, though not completely, attributable to differences in regional and total adiposity.

CONCLUSIONS

European normoglycaemic women with previous GDM display both glucoregulatory and antilipolytic insulin resistance, reduced beta-cell function and dyslipidaemia. These metabolic abnormalities are likely to contribute to their increased risk of future type 2 diabetes.

Intermediate metabolism in normal pregnancy and in gestational diabetes

Complex though integrated hormonal and metabolic changes characterize pregnancy. In the face of progressive decline in insulin action, glucose homeostasis is maintained through a compensatory increase in insulin secretion. This switches energy production from carbohydrates to lipids, making glucose readily available to the fetus. This precise and entangled hormonal and metabolic condition can, however, be disrupted and diabetic hyperglycemia can develop (gestational diabetes). The increase in plasma glucose level is believed to confer significant risk of complications to both the mother and the fetus and the newborn. Moreover, exposition of fetal tissues to the diabetic maternal environment can translate into an increased risk for development of diabetes and/or the metabolic syndrome in the adult life. In women with previous gestational diabetes, the risk of developing type 2 diabetes is greatly enhanced, to the point that GDM represents an early stage in the natural history of type 2 diabetes. In these women, accurate follow-up and prevention strategies are needed to reduce the subsequent development of overt diabetes. This paper will review current knowledge on the modifications occurring in normal pregnancy, while outlining the mechanisms. In this paper, we will review the changes of intermediary metabolism occurring during pregnancy. In particular, we will outline the mechanisms responsible for gestational diabetes; the link between these alterations and associated maternal and neonatal morbidity will be examined.

Postpartum care of the woman with diabetes

The postpartum period in women with diabetes or GDM allows both the physician and mother to relax from the intensive medical and obstetric management that has permitted, in most cases, a successful and joyous outcome. The role of the physician, however, must switch to a proactive and preventive mode to formulate a reproductive health plan for women with diabetes and GDM. The plan should be individualized to address glycemic management and surveillance, nutritional management, contraception prescription, future pregnancy planning, and lifestyle changes. Essential to the development of a reproductive health plan is the active participation of the patient, who through education gains an understanding of the far-reaching effects her active participation will have on her subsequent health and possibly on that of her future children.

History of gestational diabetes, insulin resistance and coronary risk

The purpose of this study was to examine characteristics associated with the insulin metabolic syndrome, including insulin resistance, abnormal glucose tolerance, dyslipidemia, obesity, and elevated blood pressure, among women who have experienced gestational diabetes. 39 nondiabetic, young (20-42 years), postpartum (3-18 months) white women were recruited from obstetrical clinics. Twenty-one women had a history of gestational diabetes; 18 had uncomplicated pregnancies. Multivariate analyses revealed a significant difference between groups in insulin resistance (M, measured by euglycemic clamp) and insulin levels (from an oral glucose tolerance test), with insulin resistance showing a statistically stronger difference than insulin levels. Groups also differed significantly when compared on a set of variables associated with insulin metabolic syndrome: glucose tolerance, triglycerides, blood pressure, and body-mass index. Using insulin resistance as a covariate eliminated these group differences, suggesting that insulin resistance is the key factor underlying insulin metabolic syndrome. The higher risk of later developing type 2 diabetes and hypertension in women who have a history of gestational diabetes is explicable by their poorer profile on variables associated with insulin metabolic syndrome, and appears to be attributable to insulin resistance. Thus, insulin resistance appears to distinguish young women at risk for cardiovascular disease.

TRIPOD (TRoglitazone In the Prevention Of Diabetes): a randomized, placebo-controlled trial of troglitazone in women with prior gestational diabetes mellitus

The TRoglitazone In the Prevention Of Diabetes (TRIPOD) trial is a single-center, randomized, placebo-controlled, double-masked study. The primary aim of the TRIPOD trial is to test the hypothesis that chronic administration of troglitazone to nondiabetic women with prior gestational diabetes mellitus (GDM) will improve whole-body insulin sensitivity and reduce the incidence of non-insulin-dependent diabetes (NIDDM). Because troglitazone is already known to lower blood glucose concentrations in persons who have developed NIDDM, an additional aim of the project will be to determine whether early intervention with troglitazone will achieve better final glycemic control than can be achieved by later intervention. In addition, since troglitazone treatment is expected to improve insulin sensitivity and may prevent or delay a decline in glucose tolerance, we also plan to determine whether long-term troglitazone treatment alters the development or progression of atherosclerosis. In this article we describe the experiment's design, the study's endpoints and methods for determining those endpoints, methods for assessing quality of life, and proposed methods for statistical analyses. The unique two-phase study design of the TRIPOD trial will permit testing not only of the biological question about reversal of insulin resistance and prevention of diabetes, but also of the clinical question about whether early intervention is superior to late intervention. Results from this trial will have an important impact on the monitoring and treatment of patients at high risk for NIDDM.

Measurement of glucose metabolism and insulin secretion during normal pregnancy and pregnancy complicated by gestational diabetes

Gestational diabetes affects 2-3% of pregnant women and is associated with foetal complications including macrosomia and an increased likelihood of developing diabetes in later life. We have therefore studied seven women with gestational diabetes and five control women both during the third trimester of pregnancy and again 2-3 months post-partum, using the minimal model analysis of the frequently sampled labelled ([6,6-2H2]-glucose) intravenous glucose tolerance test. Glucose tolerance (glucose Kd) was significantly reduced in the women with gestational diabetes compared with the normal pregnant women both in pregnancy (1.16 +/- 0.11 vs 1.78 +/- 0.23%/min; p < 0.05) and post-partum (1.47 +/- 0.22 vs 2.59 +/- 0.43%/min; p < 0.05) and increased significantly in the control women after delivery (p < 0.05). Glucose effectiveness was not significantly different between the women with gestational diabetes and the control group either during or after pregnancy. Insulin sensitivity was significantly lower during pregnancy than after delivery in the women with gestational diabetes (p < 0.05). There was no significant difference in basal insulin secretion in the two groups during pregnancy or post-partum. However, during pregnancy the control subjects significantly increased (p < 0.001) their insulin secretion over a period of 20 min in response to an intravenous glucose tolerance test (96.2 +/- 42.7 pmol/kg) compared with post-partum values (58.3 +/- 25.2 pmol/kg) while in the women with gestational diabetes insulin secretion was similar in pregnancy (65.5 +/- 9.3 pmol/kg) and after delivery (57.7 +/- 15.7 pmol/kg). These data suggest that the glucose intolerance in gestational diabetes compared to normal pregnancy is due to reduced insulin sensitivity and an impaired ability in gestational diabetes to increase insulin secretion in response to glucose.

The differential effects of body fat distribution on insulin and glucose metabolism during pregnancy

OBJECTIVE

Our purpose was to investigate whether maternal obesity, or more specifically body fat distribution, is associated with alterations in carbohydrate metabolism during pregnancy.

STUDY DESIGN

A longitudinal study of oral glucose tolerance tests, insulin, C peptide, and glucagon levels during each trimester and post partum was undertaken in nine lean and 14 obese women. Obese women were divided into lower body obese (n = 6, waist/hip ratio < 0.9) and upper body obese (n = 8, waist/hip ratio > or = 0.9).

RESULTS

Fasting blood glucose levels declined with advancing gestation only in lean subjects. Upper body obese women demonstrated maximal glucose response and insulin area under the curve by the second trimester, whereas lean and lower body obese women did not until the third trimester. Insulin areas were significantly elevated in upper body obese compared with lower body obese women (second trimester, p < 0.01; third trimester, p < 0.03; post partum p < 0.05). In contrast, C peptide levels were similar in obese subgroups and were significantly elevated only when compared with those of lean women. C peptide/insulin molar ratios were lower in upper body obese women during the second trimester (4.3 +/- 0.8) and third trimester (4.2 +/- 0.7) compared with lean (6.5 +/- 1.3, 6.7 +/- 0.5) and lower body obese women (7.9 +/- 1.4, 6.5 +/- 1.4) (p < 0.01). A significant relationship between waist/hip ratio and glucose level (r = 0.70, p < 0.004) and insulin areas (r = 0.76, p < 0.001) was present in late pregnancy in obese subjects.

CONCLUSIONS

Relative hyperinsulinemia and earlier maximal glucose response in upper body obese women suggests that body fat distribution may explain the metabolic heterogeneity present in obese women during pregnancy. Body fat topography may serve as a potential marker for the early development of carbohydrate intolerance during pregnancy.

Glucagon stimulation test: assessment of beta-cell function in gestational diabetes mellitus

OBJECTIVE

Because women with gestational diabetes mellitus have a risk of up to 60% for the later development of type II diabetes, we used the intravenous glucagon stimulation test to evaluate beta-cell function in pregnant women.

PATIENTS

Twenty-seven pregnant women with one or more risk factors for gestational diabetes had an intravenous beta-cell stimulation test. Glucose, C-peptide and insulin levels were measured at baseline and 5, 10 and 15 min after the administration of 1 mg glucagon. The women were classified using the 75-g oral glucose tolerance test according to World Health Organization criteria. During the oral glucose tolerance test glucose, C-peptide and insulin levels were measured at baseline and at 2 h.

RESULTS

Insulin and C-peptide responses were significantly lower in pregnant women with impaired glucose tolerance and diabetes compared with women with normal glucose tolerance.

CONCLUSION

This study shows gradually decreasing insulin secretion from normal to subnormal in pregnant women without and with glucose intolerance, and diabetes mellitus, respectively.

Hypocaloric diets and ketogenesis in the management of obese gestational diabetic women

The extent to which given levels of caloric restriction will improve glycemic status but increase plasma ketone bodies in gestational diabetic women has received little attention. After reviewing the underlying physiology, we present data on two feeding studies investigating the question. In the first, a weight-maintaining approximately 2400-kcal/day diet was fed on a metabolic ward to 12 gestational diabetic women for 1 week. In the second week, subjects were randomized to a continuation of the 2400-kcal/day diet or to a 1200-kcal/day diet. Twenty-four-hour mean glucose levels remained unchanged in the control group but declined in the calorie-restricted group (6.7 mM or 121 mg/dl in week 1 vs 5.4 mM or 97.3 mg/dl in week 2) (p less than 0.01). Nine-hour overnight fasting plasma insulin also declined but oral glucose tolerance did not improve with caloric restriction. Fasting plasma beta-hydroxybutyrate rose in the calorie-restricted group, along with an increase in ketonuria, but not in the control group. A second study compared the impact of a 33% calorie-restricted diet or insulin to a full-calorie diet in a similar 2-week experimental design and measured hepatic glucose output and insulin sensitivity with dideuterated glucose before and during an insulin clamp. Diet in three subjects improved fasting and 24-hr mean glucose by 22 and 10%, respectively, whereas prophylactic insulin in three subjects produced 0 and 4% reductions, respectively. On average, ketonuria after a 9-hr fast declined to an equivalent degree with both treatments. Hepatic glucose output and insulin sensitivity were not statistically significantly altered by gestational diabetes or the therapeutic interventions compared to nondiabetic normal weight or obese pregnant controls. In conclusion, 50% caloric restriction improves glycemic status in obese women with gestational diabetes but is associated with an increase in ketonuria, which is of uncertain significance. An intermediate 33% level of caloric restriction (to 1600-1800 kcal daily) may be more appropriate in dietary management of obese woman with gestational diabetes mellitus and more effective than prophylactic insulin. Further studies are required to confirm these findings.

Effects of yohimbine and nicotinic acid on insulin secretion in islet transplanted streptozotocin-diabetic rats

Whether insulin secretion from transplanted islets is normally regulated has not been established. We have studied the effects of either alpha-adrenoceptor antagonism or induction of insulin resistance on glucose-stimulated insulin secretion in streptozotocin (70 mg/kg)-diabetic rats transplanted with 1000 freshly isolated islets to the left kidney subcapsular space. The alpha 2-adrenoceptor antagonist yohimbine (15 micrograms/min) increased basal and potentiated glucose-stimulated insulin secretion in control rats. In contrast, yohimbine did not affect basal or glucose-stimulated insulin secretion in transplanted rats. This suggests that the alpha-adrenoceptor islet tonus is lost following islet transplantation. Induction of insulin resistance by nicotinic acid (6 mg orally twice daily for 10 days) was followed by increased basal insulin levels without any effect on basal plasma glucose levels, both in control and islet transplanted rats, as an adaptation to insulin resistance. Furthermore, after nicotinic acid, the plasma insulin response during glucose infusion was adequate to maintain the normal hyperglycemic response, both in controls and in islet transplanted rats. This suggests that transplanted islets retain the capability to adapt to insulin resistance.

[Intolerance to carbohydrates: the seven questions]

The borderline between diabetes and intolerance to carbohydrates has been drawn on the basis of prospective studies which determined a glycaemic threshold marking the risk for microangiopathy. On the other hand, the borderline between intolerance to carbohydrates and normal glucose tolerance remains arbitrary: 25% for subjects who are intolerant to carbohydrates return to normal glucose tolerance within 10 years. This is due to the fact that intolerance to carbohydrates is a heterogeneous entity which should be dismembered according to the severity of insulin deficiency and to the degree of insulin resistance. Alteration of insulin secretion is perhaps the most specific marker of susceptibility to non insulin dependent diabetes, but insulin resistance is certainly the principal factor exhausting insulin secretion and leading to non insulin dependent diabetes. Insulin resistance and the hyperinsulinism it creates seem to facilitate atherogenesis, even when glucose tolerance is still normal, so that the oral glucose tolerance test is not only poorly reproducible but loses a great deal of its value in the early detection of vascular risk. Measurements of fasting and post-prandial glucose levels and of A1C haemoglobin, cholesterol, triglyceride, and HDL cholesterol levels usually make it possible to classify subjects into one of the three following categories: (1) no risk of macro- or microangiopathy; (2) diabetes with a risk of macro- or microangiopathy; (3) intolerance to glucose with risk of atherogenesis but no risk of microangiopathy. The oral glucose tolerance test probably remains useful within a small set of values that are either very slightly above normal or dissociated. Measuring blood insulin levels might be a better way of assessing the risk of atherogenesis, but the clinical use of this test requires evaluation.

Insulin sensitivity and B-cell responsiveness to glucose during late pregnancy in lean and moderately obese women with normal glucose tolerance or mild gestational diabetes

We used the minimal model technique to obtain concurrent measurements of whole-body insulin sensitivity and pancreatic B-cell responsiveness to glucose during the third trimester of pregnancy. Insulin sensitivity in normal pregnant women (n = 8) was reduced to only one third that of a group of nonpregnant women (n = 7) of similar age and relative weight. This marked insulin resistance was compensated by reciprocal enhancement of the first and second-phase insulin responses to intravenous glucose, which were increased threefold as compared with the nonpregnant women. Women with gestational diabetes mellitus (n = 16) had mean insulin sensitivity that was similar to that of the normal pregnant group, which indicates that insulin action was appropriate for the late phase of pregnancy in the gestational diabetic group. By contrast, the mean first-phase insulin response was significantly reduced in women with gestational diabetes mellitus, as compared with that of normal pregnant women (p less than 0.001). However, approximately one fifth of the group with gestational diabetes mellitus had first-phase responses that did not fall below the 95% confidence interval for the mean in normal pregnant women. The mean second-phase response was also lower in the group with gestational diabetes, although the difference was of borderline statistical significance (p less than 0.09). Our findings reveal the quantitative nature of the reciprocal changes in insulin sensitivity and B-cell function that normally accompany late pregnancy. They further indicate that during the third trimester, mild gestational diabetes is characterized by an impairment of pancreatic B-cell function rather than an exaggeration of the normal insulin resistance of late pregnancy.

Islet function and insulin sensitivity in the non-diabetic offspring of conjugal type 2 diabetic patients

To determine whether the genetic predisposition towards Type 2 diabetes was associated with a defect in either islet-cell function or insulin action, 12 non-diabetic offspring each of whose parents both had Type 2 diabetes were studied, together with 12 control subjects matched for age, sex, and weight. Fasting plasma glucose was higher in the offspring (5.5 +/- 0.1 mmol l-1 (mean +/- SE)) than in the matched controls (5.1 +/- 0.1 mmol l-1) (p less than 0.05). Using an IVGTT insulin sensitivity was not significantly lower in the offspring compared with their controls (3.1 +/- 0.5 vs 3.8 +/- 1.0 min-1 mU-1 l 10(-4)). There was no significant difference in any of the measures of insulin secretion (first- and second-phase response to IV glucose, slope of glucose potentiation, and maximal glucose regulated insulin secretory capacity). Glucagon secretion measured before and after a stimulus of IV arginine at varying plasma glucose concentrations was virtually identical in the offspring and their controls. Among a total of 28 non-diabetic subjects of differing body-weights there was a significant inverse relationship between insulin sensitivity and insulin secretion. When adjusted for their generally lower insulin sensitivity, maximal insulin secretory capacity was reduced in the offspring (p = 0.038, one-tailed t-test). The results suggest that the genetic predisposition to Type 2 diabetes is not associated in young adults with any major pre-morbid impairment in insulin secretion or insulin action but the relationship between the two may be abnormal. Islet A-cell function appears to be normal.

Increased risk for gestational diabetes mellitus associated with insulin receptor and insulin-like growth factor II restriction fragment length polymorphisms

Gestational diabetes mellitus (GDM) is defined as glucose intolerance with onset or first recognition during pregnancy. We have examined restriction fragment length polymorphisms (RFLPs) near "candidate diabetogenic genes" as one approach to identify molecular markers for GDM genes. Genotypes for insulin hypervariable region (HVR), insulin-like growth factor II (IGF2), insulin receptor (INSR), and glucose transporter (GLUT1) RFLPs were studied in 96 GDM and 164 control subjects, matched to GDM for race, age, and gravidity. Logistic regression analysis was used to explore the relationship between genotypes at these candidate gene loci and GDM, while adjusting for the effects of potential confounding variables. Among black subjects, the INSR allele 1 (P = 0.001) and interactions between INSR allele 1 with body mass index (BMI) (P = 0.002) and history of DM in subject's mother (P = 0.004) contributed significantly to GDM risk. Among Caucasian subjects, a similar relationship between the INSR allele 1 (P = 0.007) and INSR allele 1-BMI interactions (P = 0.011) on GDM risk were observed. In Caucasians, an additional significant risk factor was determined by an INSR allele 1-IGF2 allele 2 interaction (P = 0.018). No risk factors were identified in Hispanic subjects. These data continue to support the hypothesis that GDM is a heterogeneous disorder with respect to phenotypic and genotypic features. Furthermore, our data suggest that risk for GDM in black and Caucasian subjects is not due to obesity perse but to interactions between obesity and INSR alleles. In Caucasian women, INSR and IGF2 alleles interact to confer additional risk for GDM. Thus genes underlying susceptibility to GDM in some women may be similar to genes conferring risk to NIDDM, while in others novel genes may contribute to GDM risk.

Relationship of upper body fat distribution to serum glucose and lipids in a Costa Rican population

Present models of the relation between subcutaneous fat distribution and serum biochemistries have been based largely on U.S. White populations. To determine interpopulational differences in that relation, we measured 68 clinically normal adult Costa Ricans aged 17-32. Data collected included six skinfolds: triceps, subscapular, suprailiac, umbilical, anterior mid-thigh, and medial calf; height, weight, and four fasting serum parameters: glucose, triglyceride, cholesterol, and high-density lipoprotein (HDL). Correlations between standardized skinfold ratios and biochemistries were highest--on the order of 0.40-0.50--for upper-lower body contrasts to triglyceride and cholesterol in males and to glucose and HDL in females. Canonical correlation analysis, with body mass index partialed out, found significant correlations for the first male variate and the first two female variates. The first male variate was positively weighted on subscapular fatness and on triglyceride and cholesterol, respectively. The two female skinfold variates were positively weighted on subscapular and on outer limbs, respectively, while their corresponding biochemical variates were weighted on glucose and triglyceride and on cholesterol and HDL, respectively. These findings are generally consistent with those based on U.S. populations but suggest that in non-Anglo populations, upper trunk fatness may be more relevant than anterior waist fatness to biochemical dysfunction.

Glucose, insulin and C-peptide kinetics during intravenous glucose tolerance test in chronic liver disease

To elucidate the mechanism of glucose intolerance in chronic liver disease (CLD), the kinetics of plasma glucose, insulin and C-peptide were studied after intravenous glucose loading in patients with CLD. Fasting plasma insulin levels were higher in patients with CLD than in normal subjects. This hyperinsulinemia was attributed primarily to an increased pancreatic secretion of insulin. Patients with CLD were divided into two groups, one with normal fasting plasma glucose (FBS less than 100 mg/dl (Group I) and the other with higher FBS (Group II). In Group I, the glucose disappearance rate was normal and a brisk acute insulin response (AIR) to glucose was noted. The glucose disappearance rate in Group II was lower than that in normal subjects, and AIR to glucose was blunted. It is suggested that normal glucose tolerance in Group I patients could be interpreted as a state of compensation by hypersecretion of insulin. On the other hand, the glucose intolerance in Group II patients could be due to inadequate insulin secretion to overcome insulin resistance of CLD.

Body fat distribution and hyperinsulinemia as risk factors for diabetes and cardiovascular disease

Differences in body fat distribution between diabetics and nondiabetics have been recognized for several decades; diabetics have a more centralized or upper body fat pattern than nondiabetics. Recently, attention has focused on fat patterning and also on hyperinsulinemia as possible risk factors for cardiovascular disease, as well. The case for insulin as a cardiovascular risk factor is bolstered by theoretical considerations related to its possibly atherogenic effects on serum and arterial wall lipids. Empirical evidence for fat patterning and hyperinsulinemia as cardiovascular risk factors rests on six prospective epidemiologic studies, three on fat patterning and three on insulin. Although provocative, none of these studies can be regarded as definitive. In none was a dose-response effect demonstrated, and there are various inconsistencies within and across the studies. Moreover, in none of the studies were hyperinsulinemia and fat patterning evaluated simultaneously. This is of particular importance in view of the well-documented interrelationships between these two variables. For example, insulin resistance and hyperinsulinemia have been found to be greater in women with upper body obesity compared to women with lower body obesity of equivalent degree. Considerable progress has been made recently in understanding the mechanisms of the differential metabolic effects of these two types of obesity. The extent to which fat patterning and hyperinsulinemia are genetic or acquired has received relatively little attention. Further research on this question is warranted since elucidation of any environmental influences on these variables might suggest new clinical and public health control measures.