The feto-placental glucose steal phenomenon is a major cause of maternal metabolic adaptation during late pregnancy in the rat

Randomized study of the effects of empagliflozin and topiramate dual therapy on anthropometric and metabolic indices in non-diabetic individuals with overweight/obesity on a calorie-restricted diet

OBJECTIVES

The objective of this study was to evaluate the effectiveness of the combined use of empagliflozin (EMPA) and topiramate (TPM) versus a placebo in overweight/obese individuals without diabetes on a calorie-restricted diet.

METHODS

In this study, 44 non-diabetic and overweight/obese subjects who were on a calorie restricted diet were randomly assigned into 2 groups: (1) Participants received a 10 mg EMPA tablet daily plus TPM tablet (at the 1st week 25 mg once a day and from the second week 25 mg twice a day); (2) Participants received an empagliflozin placebo (daily) plus a topiramate placebo (as mentioned for topiramate tablet in group 1), for 12 weeks. At baseline and weeks 4, 8, 12, weight, height, body mass index (BMI), waist circumference (WC), and body composition were evaluated. Before and after the intervention, blood pressure, C reactive protein, and glucose and lipid profile parameters were measured.

RESULTS

The EMPA/TPM group, compared to placebo, had a greater percent change of weight at week 12 (- 8.92 ± 1.80 vs. - 4.93 ± 1.17). The intervention group had a greater percent change of fat mass and fat percent at week 12 (P < 0.05). However, there was no difference in the percent of change in fat-free percent between the two groups at week 12 (P = 0.577). Within-group analysis found a significant reduction in SBP, DBP, FBS, insulin, HOMA-IR, TC, LDL, HDL, TG, and CRP in both groups (P < 0.05). At week 12, no statistically significant difference was observed between the two groups in any of mentioned variables (P > 0.05).

CONCLUSION

In non-diabetic overweight/obese individuals, the combination of EMPA/TPM and calorie restriction led to a notable decrease in body weight and was generally well-tolerated. Further research is required to evaluate the potential advantages of utilizing this combination for sustained weight management in the long run.

LEVEL I

Randomized clinical trial.

Insulin Blood Levels in Gestational Diabetes Mellitus in Relation to Ethnicity and Age in the Kingdom of Bahrain: A Cross-Sectional Study

BACKGROUND

Gestational diabetes mellitus (GDM) is one of the most common complications of pregnancy. It may be attributed to certain placental hormones during pregnancy which render insulin less effective. Our study aimed to focus on the levels of insulin in gestational diabetic women in the Kingdom of Bahrain as compared with non-diabetic pregnant women. Furthermore, we studied the correlation between insulin levels by ethnicity and age of the pregnant women.  Methods: A cross-sectional study was conducted on 75 pregnant participants: 41 with GDM (test group) and 34 without GDM (control group). Insulin levels were determined in patients with GDM and compared to non-diabetic pregnant women. A comparison between Bahraini and non-Bahraini women was carried out in two different age groups: below and above 30 years of age. P values < 0.05 were considered significant.

RESULTS

The results showed higher mean values of fasting blood glucose (FBG), random blood glucose (RBG), and insulin levels in the test group when compared to the control group. There was no significant difference in FBG, RBG, and insulin levels among Bahraini women with GDM and non-Bahraini women (Indian, Pakistani. Bengali, and Filipino) with GDM. Age, less than 30 vs more than 30 years, had no significant effect on women with GDM.

CONCLUSION

Insulin levels were higher in pregnant women with GDM irrespective of their ethnicity or age. The lack of blood glucose control in GDM even in the presence of high insulin secretion may suggest loss of insulin effectiveness due to other factors such as stress and lactogenic placental hormones.

Human Milk Oligosaccharides in Maternal Serum Respond to Oral Glucose Load and Are Associated with Insulin Sensitivity

(1) Background: Pregnancy presents a challenge to maternal glucose homeostasis; suboptimal adaptations can lead to gestational diabetes mellitus (GDM). Human milk oligosaccharides (HMOs) circulate in maternal blood in pregnancy and are altered with GDM, suggesting influence of glucose homeostasis on HMOs. We thus assessed the HMO response to glucose load during an oral glucose tolerance test (OGTT) and investigated HMO associations with glucose tolerance/insulin sensitivity in healthy pregnant women. (2) Methods: Serum of 99 women, collected at 0 h, 1 h and 2 h during a 75 g OGTT at 24-28 gestational weeks was analyzed for HMOs (2'FL, 3'SLN, LDFT, 3'SL) by HPLC; plasma glucose, insulin and C-peptide were analyzed by standard biochemistry methods. (3) Results: Serum 3'SL concentrations significantly increased from fasting to 1 h after glucose load, while concentrations of the other HMOs were unaltered. Higher 3'SL at all OGTT time points was associated with a generally more diabetogenic profile, with higher hepatic insulin resistance (HOMA-IR), lower insulin sensitivity (Matsuda index) and higher insulin secretion (C-peptide index 1). (4) Conclusions: Rapid increase in serum 3'SL post-oral glucose load (fasted-fed transition) indicates utilization of plasma glucose, potentially for sialylation of lactose. Associations of sialylated HMOs with a more diabetogenic profile suggest sustained adaptations to impaired glucose homeostasis in pregnancy. Underlying mechanisms or potential consequences of observed HMO changes remain to be elucidated.

Placental nutrient transporters adapt during persistent maternal hypoglycaemia in rats

Maternal malnutrition is associated with decreased nutrient transfer to the foetus, which may lead to foetal growth restriction, predisposing children to a variety of diseases. However, regulation of placental nutrient transfer during decreased nutrient availability is not fully understood. In the present study, the aim was to investigate changes in levels of placental nutrient transporters accompanying maternal hypoglycaemia following different durations and stages of gestation in rats. Maternal hypoglycaemia was induced by insulin-infusion throughout gestation until gestation day (GD)20 or until end of organogenesis (GD17), with sacrifice on GD17 or GD20. Protein levels of placental glucose transporters GLUT1 (45/55 kDa isotypes) and GLUT3, amino acid transporters SNAT1 and SNAT2, and insulin receptor (InsR) were assessed. On GD17, GLUT1-45, GLUT3, and SNAT1 levels were increased and InsR levels decreased versus controls. On GD20, following hypoglycaemia throughout gestation, GLUT3 levels were increased, GLUT1-55 showed the same trend. After cessation of hypoglycaemia at end of organogenesis, GLUT1-55, GLUT3, and InsR levels were increased versus controls, whereas SNAT1 levels were decreased. The increases in levels of placental nutrient transporters seen during maternal hypoglycaemia and hyperinsulinemia likely reflect an adaptive response to optimise foetal nutrient supply and development during limited availability of glucose.

Impact of preconception weight loss on fasting glucose and pregnancy outcomes in women with obesity: A randomized trial

OBJECTIVE

This study examined the effectiveness of a nonsurgical, preconception weight loss intervention on pregnancy outcomes in women with obesity.

METHODS

This was a two-arm, parallel-group randomized controlled trial. A total of 164 women with BMI 30 to 55 kg/m² who were aged 18 to 38 years and planning pregnancy were randomized to a 12-week standard dietary intervention (SDI; n = 79) or a modified very low-energy diet (VLED; n = 85). Participants were observed for ≤48 weeks while trying for pregnancy and then during pregnancy. The primary outcome was maternal fasting plasma glucose at 26 to 28 weeks' gestation. Exploratory outcomes were individual and composite obesity-related adverse pregnancy outcomes.

RESULTS

Weight loss was greater in the VLED group (SDI 3.2 [0.6] kg vs. VLED 13.0 [0.5] kg, p < 0.01). In completers who had a singleton live birth (SDI 22/79 vs. VLED 35/85, p = 0.10), there was no difference in fasting glucose at 26 to 28 weeks' gestation (SDI 4.8[0.2] mmol/L vs. VLED 4.6 [0.1] mmol/L, p = 0.42). However, the composite of adverse pregnancy outcomes was significantly lower in the VLED group (p < 0.001).

CONCLUSIONS

Substantial prepregnancy weight loss in women with obesity does not alter fasting glucose at 26 to 28 weeks' gestation but does reduce a composite of adverse pregnancy outcomes. A better understanding of metabolic changes in pregnancy after preconception weight loss may assist in improving maternal and neonatal health outcomes.

Effects of snack intake during pregnancy and lactation on reproductive outcome in mild hyperglycemic rats

Metabolic disorders, like diabetes, as well as maternal diet, alter nutrient availability in utero, inducing adaptations in the offspring. Whether the effects of maternal hyperglycemia are modulated by diet, however, has yet to be explored. In the current study, we examined this issue by giving females rats, treated neonatally with STZ to induce mild hyperglycemia, and control littermates either ad libitum access to standard chow (Control n = 17; STZ n = 16) or standard chow and snacks (Control-snack n = 18; STZ-snack n = 19) (potato chips and a red fruit-flavored sucrose syrup solution 1.5%) throughout pregnancy and lactation. We hypothesized that the maternal glucose intolerance typically seen in female rats treated neonatally with STZ would be exacerbated by snack intake, and that the combination of snack intake and STZ treatment would lead to alterations in maternal behavior and offspring development. Maternal body weight and food intake were measured daily through pregnancy and lactation and litter weight throughout lactation. At birth, litter size, offspring weight, body length, and anogenital distance were obtained and offspring were classified according to their weight. Measures of nursing and retrieval behavior, as well as exploration in the open field and the elevated plus-maze were also recorded. As predicted, snack intake tended to aggravate the glucose intolerance of STZ-treated rats during pregnancy. Both Control and STZ-treated females that had access to snacks ate more calories and fat, but less carbohydrate and protein than females having access to chow alone. Overall, STZ-treated dams gave birth to fewer pups. Chow-fed STZ females gave birth to a greater proportion of large for pregnancy age pups, whereas dams in the Control-snack group gave birth to a greater proportion of small pups. The birth weight classification of pups born to STZ-snack rats, however, resembled that of the Control chow-fed females. Although all litters gained weight during lactation, litters from snack-fed dams gained less weight regardless of maternal hyperglycemia and did not show catch-up growth by weaning. Overall, STZ rats spent more time nest building, whereas the average inter milk ejection interval was higher in snack-fed females. STZ-snack dams retrieved the complete litter faster than dams in the other groups. Together, these data suggest that when mild hyperglycemic females are given access to snacks throughout pregnancy and lactation their intake is similar to that of Control females given snack access. The combination of hyperglycemia and snack access tended to decrease glucose tolerance in pregnancy, and normalized birth weight classification, but produced few other effects that were not seen as a function of snack intake or hyperglycemia alone. Since birth weight is a strong predictor of health issues, future studies will further investigate offspring behavioral and metabolic outcomes later in life.

Central actions of insulin during pregnancy and lactation

Pregnancy and lactation are highly metabolically demanding states. Maternal glucose is a key fuel source for the growth and development of the fetus, as well as for the production of milk during lactation. Hence, the maternal body undergoes major adaptations in the systems regulating glucose homeostasis to cope with the increased demand for glucose. As part of these changes, insulin levels are elevated during pregnancy and lower in lactation. The increased insulin secretion during pregnancy plays a vital role in the periphery; however, the potential effects of increased insulin action in the brain have not been widely investigated. In this review, we consider the impact of pregnancy on brain access and brain levels of insulin. Moreover, we explore the hypothesis that pregnancy is associated with site-specific central insulin resistance that is adaptive, allowing for the increases in peripheral insulin secretion without the consequences of increased central and peripheral insulin functions, such as to stimulate glucose uptake into maternal tissues or to inhibit food intake. Conversely, the loss of central insulin actions may impair other functions, such as insulin control of the autonomic nervous system. The potential role of low insulin in facilitating adaptive responses to lactation, such as hyperphagia and suppression of reproductive function, are also discussed. We end the review with a list of key research questions requiring resolution.

Maternal pineal melatonin in gestation and lactation physiology, and in fetal development and programming

Pregnancy and lactation are reproductive processes that rely on physiological adaptations that should be timely and adequately triggered to guarantee both maternal and fetal health. Pineal melatonin is a hormone that presents daily and seasonal variations that synchronizes the organism's physiology to the different demands across time through its specific mechanisms and ways of action. The reproductive system is a notable target for melatonin as it actively participates on reproductive physiology and regulates the hypothalamus-pituitary-gonads axis, influencing gonadotropins and sexual hormones synthesis and release. For its antioxidant properties, melatonin is also vital for the oocytes and spermatozoa quality and viability, and for blastocyst development. Maternal pineal melatonin blood levels increase during pregnancy and triggers the maternal physiological alterations in energy metabolism both during pregnancy and lactation to cope with the energy demands of both periods and to promote adequate mammary gland development. Moreover, maternal melatonin freely crosses the placenta and is the only source of this hormone to the fetus. It importantly times the conceptus physiology and influences its development and programing of several functions that depend on neural and brain development, ultimately priming adult behavior and energy and glucose metabolism. The present review aims to explain the above listed melatonin functions, including the potential alterations observed in the progeny gestated under maternal chronodisruption and/or hypomelatoninemia.

The Role of Fatty Acid Signaling in Islet Beta-Cell Adaptation to Normal Pregnancy

BACKGROUND

Maintenance of a normal fetal nutrient supply requires major adaptations in maternal metabolic physiology, including of the islet beta-cell. The role of lipid signaling processes in the mechanisms of islet beta-cell adaptation to pregnancy has been minimally investigated.

OBJECTIVE

To determine the effects of pregnancy on islet fatty acid (FA) metabolic partitioning and FA augmentation of glucose-stimulated insulin secretion (GSIS).

METHODS

Age matched virgin, early pregnant (gestational day-11, G11) and late pregnant (G19) Sprague-Dawley rats were studied. Fasted and fed state biochemistry, oral glucose tolerance tests (OGTT), and fasted and post-OGTT liver glycogen, were determined to assess in vivo metabolic characteristics. In isolated islets, FA (BSA-bound palmitate 0.25 mmol/l) augmentation of GSIS, FA partitioning into esterification and oxidation processes using metabolic tracer techniques, lipolysis by glycerol release, triacylglycerols (TG) content, and the expression of key beta-cell genes were determined.

RESULTS

Plasma glucose in pregnancy was lower, including during the OGTT (glucose area under the curve 0-120 min (AUC_0-120); 655±24 versus 849±13 mmol.l^-1.min; G19 vs virgin; P<0.0001), with plasma insulin concentrations equivalent to those of virgin rats (insulin AUC_0-120; 97±7 versus 83±7 ng.ml^-1.min; G19 vs virgin; not significant). Liver glycogen was depleted in fasted G19 rats with full recovery after oral glucose. Serum TG increased during pregnancy (4.4±0.4, 6.7±0.5; 17.1±1.5 mmol/l; virgin, G11, G19, P<0.0001), and islet TG content decreased (147±42, 172±27, 73±13 ng/µg protein; virgin, G11, G19; P<0.01). GSIS in isolated islets was increased in G19 compared to virgin rats, and this effect was augmented in the presence of FA. FA esterification into phospholipids, monoacylglycerols and TG were increased, whereas FA oxidation was reduced, in islets of pregnant compared to virgin rats, with variable effects on lipolysis dependent on gestational age. Expression of Ppargc1a, a key regulator of mitochondrial metabolism, was reduced by 51% in G11 and 64% in G19 pregnant rat islets compared to virgin rat islets (P<0.001).

CONCLUSION

A lowered set-point for islet and hepatic glucose homeostasis in the pregnant rat has been confirmed. Islet adaptation to pregnancy includes increased FA esterification, reduced FA oxidation, and enhanced FA augmentation of glucose-stimulated insulin secretion.

The Hepatobiliary System: An Overview of Normal Function and Diagnostic Testing in Pregnancy

Pregnancy is associated with physiological adaptions that affect every organ system. Changes in liver function in pregnancy have important effects on nutrient metabolism, protein synthesis, and the biotransformation of substances in preparation for excretion. A clear understanding of the anatomic and functional changes of the hepatobiliary system is necessary for the diagnosis and evaluation of disease, as well as understanding how these changes predispose women to pregnancy-specific hepatic conditions. In this review, the effect of gestational changes in hepatobiliary function on laboratory tests and the role of diagnostic imaging of the liver and gallbladder in pregnancy will be discussed.

Resistance to the sympathoexcitatory effects of insulin and leptin in late pregnant rats

KEY POINTS

Pregnancy increases sympathetic nerve activity (SNA), although the mechanisms responsible for this remain unknown. We tested whether insulin or leptin, two sympathoexcitatory hormones increased during pregnancy, contribute to this. Transport of insulin across the blood-brain barrier in some brain regions, and into the cerebrospinal fluid (CSF), was increased, although brain insulin degradation was also increased. As a result, brain and CSF insulin levels were not different between pregnant and non-pregnant rats. The sympathoexcitatory responses to insulin and leptin were abolished in pregnant rats. Blockade of arcuate nucleus insulin receptors did not lower SNA in pregnant or non-pregnant rats. Collectively, these data suggest that pregnancy renders the brain resistant to the sympathoexcitatory effects of insulin and leptin, and that these hormones do not mediate pregnancy-induced sympathoexcitation. Increased muscle SNA stimulates glucose uptake. Therefore, during pregnancy, peripheral insulin resistance coupled with blunted insulin- and leptin-induced sympathoexcitation ensures adequate delivery of glucose to the fetus.

ABSTRACT

Pregnancy increases basal sympathetic nerve activity (SNA), although the mechanism responsible for this remains unknown. Insulin and leptin are two sympathoexcitatory hormones that increase during pregnancy, yet, pregnancy impairs central insulin- and leptin-induced signalling. Therefore, to test whether insulin or leptin contribute to basal sympathoexcitation or, instead, whether pregnancy induces resistance to the sympathoexcitatory effects of insulin and leptin, we investigated α-chloralose anaesthetized late pregnant rats, which exhibited increases in lumbar SNA (LSNA), splanchnic SNA and heart rate (HR) compared to non-pregnant animals. In pregnant rats, transport of insulin into cerebrospinal fluid and across the blood-brain barrier in some brain regions increased, although brain insulin degradation was also increased; brain and cerebrospinal fluid insulin levels were not different between pregnant and non-pregnant rats. Although i.c.v. insulin increased LSNA and HR and baroreflex control of LSNA and HR in non-pregnant rats, these effects were abolished in pregnant rats. In parallel, pregnancy completely prevented the actions of leptin with respect to increasing lumbar, splanchnic and renal SNA, as well as baroreflex control of SNA. Blockade of insulin receptors (with S961) in the arcuate nucleus, the site of action of insulin, did not decrease LSNA in pregnant rats, despite blocking the effects of exogenous insulin. Thus, pregnancy is associated with central resistance to insulin and leptin, and these hormones are not responsible for the increased basal SNA of pregnancy. Because increases in LSNA to skeletal muscle stimulates glucose uptake, blunted insulin- and leptin-induced sympathoexcitation reinforces systemic insulin resistance, thereby increasing the delivery of glucose to the fetus.

Apolipoprotein A-I Protects Against Pregnancy-Induced Insulin Resistance in Rats

Objective- Insulin resistance and inflammation in pregnancy are risk factors for gestational diabetes mellitus. Increased plasma HDL (high-density lipoprotein) and apo (apolipoprotein) A-I levels have been reported to improve glucose metabolism and inhibit inflammation in animals and humans. This study asks whether increasing plasma apoA-I levels improves insulin sensitivity and reduces inflammation in insulin-resistant pregnant rats. Approach and Results- Insulin-resistant pregnant rats received intravenous infusions of lipid-free apoA-I (8 mg/kg) or saline on days 6, 9, 12, 15, and 18 of pregnancy. The rats were then subjected to a euglycemic-hyperinsulinemic clamp. Glucose uptake was increased in white and brown adipose tissue by 57±13% and 32±10%, respectively ( P<0.05 for both), and in quadriceps and gastrocnemius muscle by 35±9.7% and 47±14%, respectively ( P<0.05 for both), in the apoA-I-treated pregnant rats relative to saline-infused pregnant rats. The pregnant rats that were treated with apoA-I also had reduced plasma TNF-α (tumor necrosis factor-α) levels by 57±8.4%, plasma IL (interleukin)-6 levels by 67±9.5%, and adipose tissue macrophage content by 54±8.2% ( P<0.05 for all) relative to the saline-treated pregnant rats. Conclusions- These studies establish that apoA-I protects against pregnancy-induced insulin resistance in rats by increasing insulin sensitivity in adipose tissue and skeletal muscle and inhibiting inflammation. This identifies apoA-I as a potential target for preventing pregnancy-induced insulin resistance and reducing the incidence of gestational diabetes mellitus.

(Re)generating Human Beta Cells: Status, Pitfalls, and Perspectives

Diabetes mellitus results from disturbed glucose homeostasis due to an absolute (type 1) or relative (type 2) deficiency of insulin, a peptide hormone almost exclusively produced by the beta cells of the endocrine pancreas in a tightly regulated manner. Current therapy only delays disease progression through insulin injection and/or oral medications that increase insulin secretion or sensitivity, decrease hepatic glucose production, or promote glucosuria. These drugs have turned diabetes into a chronic disease as they do not solve the underlying beta cell defects or entirely prevent the long-term complications of hyperglycemia. Beta cell replacement through islet transplantation is a more physiological therapeutic alternative but is severely hampered by donor shortage and immune rejection. A curative strategy should combine newer approaches to immunomodulation with beta cell replacement. Success of this approach depends on the development of practical methods for generating beta cells, either in vitro or in situ through beta cell replication or beta cell differentiation. This review provides an overview of human beta cell generation.

Region-Specific Suppression of Hypothalamic Responses to Insulin To Adapt to Elevated Maternal Insulin Secretion During Pregnancy

As part of the adaptation of maternal glucose regulation during pregnancy to ensure glucose provision to the fetus, maternal insulin concentrations become elevated. However, increased central actions of insulin, such as suppression of appetite, would be maladaptive during pregnancy. We hypothesized that central nervous system targets of insulin become less responsive during pregnancy to prevent overstimulation by the increased circulating insulin concentrations. To test this hypothesis, we have measured insulin-induced phosphorylation of Akt (pAkt) in specific hypothalamic nuclei as an index of hypothalamic insulin responsiveness. Despite higher endogenous insulin concentrations following feeding, arcuate nucleus pAkt levels were significantly lower in the pregnant group compared with the nonpregnant group. In response to an intracerebroventricular injection of insulin, insulin-induced pAkt was significantly reduced in the arcuate nucleus and ventromedial nucleus of pregnant rats compared with nonpregnant rats. Similar levels of insulin receptor β and PTEN, a negative regulator of the phosphoinositide 3-kinase/Akt pathway, were detected in hypothalamic areas of nonpregnant and pregnant rats. In the ventromedial nucleus, however, levels of phosphorylated PTEN were significantly lower in pregnancy, suggesting that reduced inactivation of PTEN may contribute to the attenuated insulin signaling in this area during pregnancy. In conclusion, these results demonstrate region-specific changes in responsiveness to insulin in the hypothalamus during pregnancy that may represent an adaptive response to minimize the impact of elevated circulating insulin on the maternal brain.

Lifetime Exposure to a Constant Environment Amplifies the Impact of a Fructose-Rich Diet on Glucose Homeostasis during Pregnancy

The need to refine rodent models of human-related disease is now being recognized, in particular the rearing environment that can profoundly modulate metabolic regulation. Most studies on pregnancy and fetal development purchase and transport young females into the research facility, which after a short period of acclimation are investigated (Gen0). We demonstrate that female offspring (Gen1) show an exaggerated hyperinsulinemic response to pregnancy when fed a standard diet and with high fructose intake, which continues throughout pregnancy. Markers of maternal hepatic metabolism were differentially influenced, as the gene expression of acetyl-CoA-carboxylase was raised in Gen1 given fructose and controls, whereas glucose transporter 5 and fatty acid synthase expression were only raised with fructose. Gen1 rats weighed more than Gen0 throughout the study, although fructose feeding raised the percent body fat but not body weight. We show that long-term habituation to the living environment has a profound impact on the animal’s metabolic responses to nutritional intervention and pregnancy. This has important implications for interpreting many studies investigating the influence of maternal consumption of fructose on pregnancy outcomes and offspring to date.

β-Cell adaptation in pregnancy

Pregnancy in placental mammals places unique demands on the insulin-producing β-cells in the pancreatic islets of Langerhans. The pancreas anticipates the increase in insulin resistance that occurs late in pregnancy by increasing β-cell numbers and function earlier in pregnancy. In rodents, this β-cell expansion depends on secreted placental lactogens that signal through the prolactin receptor. Then at the end of pregnancy, the β-cell population contracts back to its pre-pregnancy size. In the current review, we focus on how glucose metabolism changes during pregnancy, how β-cells anticipate these changes through their response to lactogens and what molecular mechanisms guide the adaptive compensation. In addition, we summarize current knowledge of β-cell adaptation during human pregnancy and what happens when adaptation fails and gestational diabetes ensues. A better understanding of human β-cell adaptation to pregnancy would benefit efforts to predict, prevent and treat gestational diabetes.

The fetal glucose steal: an underappreciated phenomenon in diabetic pregnancy

Adverse neonatal outcomes continue to be high for mothers with type 1 and type 2 diabetes, and are far from eliminated in mothers with gestational diabetes mellitus. This is often despite seemingly satisfactory glycaemic control in the latter half of pregnancy. Here we argue that this could be a consequence of the early establishment of fetal hyperinsulinaemia, a driver that exaggerates the fetal glucose steal. Essentially, fetal hyperinsulinaemia, through its effect on lowering fetal glycaemia, will increase the glucose concentration gradient across the placenta and consequently the glucose flux to the fetus. While the steepness of this gradient and glucose flux will be greatest at times when maternal hyperglycaemia and fetal hyperinsulinaemia coexist, fetal hyperinsulinaemia will favour a persistently high glucose flux even at times when maternal blood glucose is normal. The obvious implication is that glycaemic control needs to be optimised very early in pregnancy to prevent the establishment of fetal hyperinsulinaemia, further supporting the need for pre-pregnancy planning and early establishment of maternal glycaemic control. An exaggerated glucose steal by a hyperinsulinaemic fetus could also attenuate maternal glucose levels during an OGTT, providing an explanation for why some mothers with fetuses with all the characteristics of diabetic fetopathy have 'normal' glucose tolerance.

Investigating the metabolic fingerprint of term infants with normal and increased fetal growth

An NMR metabolomic approach was employed to highlight the metabolic changes underlying prenatal disorders and determine metabolites that could serve as potential markers in relation to large for gestational age (LGA) newborns.

Relationship between gestational fasting plasma glucose and neonatal birth weight, prenatal blood pressure and dystocia in pregnant Chinese women

BACKGROUND

Little is known about the optimal cut-off point of fasting plasma glucose for the diagnosis of gestational diabetes mellitus for pregnant Chinese women. This study investigates the relationship between gestational fasting plasma glucose and several variables: neonatal birth weight, prenatal blood pressure and dystocia rate of pregnant women. In this study, we hoped to provide a useful tool to screen gestational diabetes mellitus in pregnant Chinese women.

METHODS

For 1058 pregnant women enrolled in our hospital at pregnancy weeks 22-30, fasting plasma glucose, neonatal birth weight and prenatal blood pressure, as well as dystocia conditions, were examined. We analysed the correlations between the following: gestational fasting plasma glucose and neonatal birth weight; prenatal blood pressure and gestational fasting plasma glucose as well as dystocia rate and gestational fasting plasma glucose group.

RESULTS

A modest correlation was observed between gestational fasting plasma glucose and neonatal birth weight (r = 0.093, p = 0.003). The macrosomia rate was smallest when the gestational fasting plasma glucose was in the range 3.51-5.5 mmol/L. Prenatal blood pressure increased linearly with increasing gestational fasting plasma glucose (p = 0.000). There was a significant difference between the dystocia rates in different fasting plasma glucose groups (chi-squared = 13.015, p = 0.043). The results showed that the dystocia rate significantly increased when gestational fasting plasma glucose was >4.9 mmol/L; p = 0.03, OR = 2.156 (95% CI, 1.077-4.318).

CONCLUSION

We suggest that the optimal range of gestational fasting plasma glucose for pregnant Chinese women is in the range 3.5-4.9 mmol/L.

Maternal adaptations and inheritance in the transgenerational programming of adult disease

Adverse exposures in utero have long been linked with an increased susceptibility to adult cardio-renal and metabolic diseases. Clear gender differences exist, whereby growth-restricted females, although exhibiting some phenotypic modifications, are often protected from overt disease outcomes. One of the greatest physiological challenges facing the female gender, however, is that of pregnancy; yet little research has focused on the outcomes associated with this, as a potential 'second-hit' for those who were small at birth. We review the limited evidence suggesting that pregnancy may unmask cardio-renal and metabolic disease states and the consequences for long-term maternal health in females who were born small. Additionally, a growing area of research in this programming field is in the transgenerational transmission of low birth weight and disease susceptibility. Pathways for transmission might include an abnormal adaptation to pregnancy by the growth-restricted mother and/or inheritance via the parental germline. Strategies to optimise the pregnancy environment and/or prevent the consequences of inheritance of programmed deficits and dysfunction are of critical importance for future generations.

The role of oxidative stress in the pathophysiology of gestational diabetes mellitus

Normal human pregnancy is considered a state of enhanced oxidative stress. In pregnancy, it plays important roles in embryo development, implantation, placental development and function, fetal development, and labor. However, pathologic pregnancies, including gestational diabetes mellitus (GDM), are associated with a heightened level of oxidative stress, owing to both overproduction of free radicals and/or a defect in the antioxidant defenses. This has important implications on the mother, placental function, and fetal well-being. Animal models of diabetes have confirmed the important role of oxidative stress in the etiology of congenital malformations; the relative immaturity of the antioxidant system facilitates the exposure of embryos and fetuses to the damaging effects of oxidative stress. Of note, there are only a few clinical studies evaluating the potential beneficial effects of antioxidants in GDM. Thus, whether or not increased antioxidant intake can reduce the complications of GDM in both mother and fetus needs to be explored. This review provides an overview and updated data on our current understanding of the complications associated with oxidative changes in GDM.

A primary defect in glucose production alone cannot induce glucose intolerance without defects in insulin secretion

Increased glucose production is associated with fasting hyperglycaemia in type 2 diabetes but whether or not it causes glucose intolerance is unclear. This study sought to determine whether a primary defect in gluconeogenesis (GNG) resulting in elevated glucose production is sufficient to induce glucose intolerance in the absence of insulin resistance and impaired insulin secretion. Progression of glucose intolerance was assessed in phosphoenolpyruvate carboxykinase (PEPCK) transgenic rats, a genetic model with a primary increase in GNG. Young (4-5 weeks of age) and adult (12-14 weeks of age) PEPCK transgenic and Piebald Virol Glaxo (PVG/c) control rats were studied. GNG, insulin sensitivity, insulin secretion and glucose tolerance were assessed by intraperitoneal and intravascular substrate tolerance tests and hyperinsulinaemic/euglycaemic clamps. Despite elevated GNG and increased glucose appearance, PEPCK transgenic rats displayed normal glucose tolerance due to adequate glucose disposal and robust glucose-mediated insulin secretion. Glucose intolerance only became apparent in the PEPCK transgenic rats following the development of insulin resistance (both hepatic and peripheral) and defective glucose-mediated insulin secretion. Taken together, a single genetic defect in GNG leading to increased glucose production does not adversely affect glucose tolerance. Insulin resistance and impaired glucose-mediated insulin secretion are required to precipitate glucose intolerance in a setting of chronic glucose oversupply.

Maternal glycemia and risk of large-for-gestational-age babies in a population-based screening

OBJECTIVE

Gestational diabetes is a risk factor for large-for-gestational-age (LGA) newborns, but many LGA babies are born to mothers with normal glucose tolerance. We aimed to clarify the association of maternal glycemia across the whole distribution with birth weight and risk of LGA births in mothers with normal glucose tolerance.

RESEARCH DESIGN AND METHODS

We undertook a population-based gestational diabetes screening in an urban area of Hungary in 2002-2005. All singleton pregnancies of mothers >or=18 years of age, without known diabetes or gestational diabetes (World Health Organization criteria) and data on a 75-g oral glucose tolerance test at 22-30 weeks of gestation, were included (n = 3,787, 78.9% of the target population). LGA was determined as birth weight greater than the 90th percentile using national sex- and gestational age-specific charts.

RESULTS

Mean +/- SD maternal age was 30 +/- 4 years, BMI was 22.6 +/- 4.0 kg/m(2), fasting blood glucose was 4.5 +/- 0.5 mmol/l, and postload glucose was 5.5 +/- 1.0 mmol/l. The mean birth weight was 3,450 +/- 476 g at 39.2 +/- 1.2 weeks of gestation. There was a U-shaped association of maternal fasting glucose with birth weight (P(curve) = 0.004) and risk of having an LGA baby (lowest values between 4 and 4.5 mmol/l, P(curve) = 0.0004) with little change after adjustments for clinical characteristics. The association of postload glucose with birth weight (P = 0.03) and the risk of an LGA baby (P = 0.09) was weaker and linear.

CONCLUSIONS

Both low and high fasting glucose values at 22-30 weeks of gestation are associated with increased risk of an LGA newborn. We suggest that the excess risk related to low glucose reflects the increased use of nutrients by LGA fetuses that also affects the mothers' fasting glucose.

Pregnancy impairs baroreflex control of heart rate in rats: role of insulin sensitivity

Recent studies in rabbits suggest that insulin resistance and reduced brain insulin contribute to impaired baroreflex control of heart rate (HR) during pregnancy; however, the mechanisms are unknown. The rat model is ideal to investigate these mechanisms because much is known about rat brain baroreflex neurocircuitry and insulin receptor locations. However, it is unclear in rats whether pregnancy impairs the HR baroreflex or whether insulin resistance is involved. Therefore, this study tested the hypothesis that in rats pregnancy decreases HR baroreflex sensitivity (BRS) and that this decrease is related to concurrent decreases in insulin sensitivity (IS). BRS was quantified before, during, and after pregnancy using complementary methods: 1) spontaneous BRS (sBRS) derived from sequence method analysis of telemetric, continuous arterial pressure recordings; and 2) maximal BRS of complete sigmoidal baroreflex relationships. IS was measured (hyperinsulinemic euglycemic clamp) to determine whether BRS and IS change in parallel. sBRS was reduced at midgestation [pregnancy day 10 (P10)], returned to nonpregnant (NP) levels on P18, and fell again at late gestation (P20) (sBRS in ms/mmHg: NP, 1.66 + or - 0.04; P10, 1.17 + or - 0.11; P18, 1.55 + or - 0.12; P20, 1.31 + or - 0.05; n = 5; P < 0.05). Similar triphasic patterns were observed for both maximal BRS [in beats x min(-1) x mmHg(-1): NP, 4.45 + or - 0.52 (n = 10); P11-12, 2.76 + or - 0.11 (n = 7); P17-18, 3.79 + or - 0.14 (n = 5); P19-20, 2.32 + or - 0.40 (n = 8); P < 0.0001] and previous and current measurements of IS (in mg glucose x kg(-1) x min(-1): NP, 32 + or - 2; P19-20, 15 + or - 1; P < 0.0005). Furthermore, during pregnancy, the standard deviation (SD) of MAP increased, and the SD of HR decreased, indirectly suggesting baroreflex impairment. sBRS increased transiently during parturition, and sBRS, maximal BRS, and IS normalized 3-4 days postpartum. In conclusion, pregnancy decreases HR BRS in rats. The parallel temporal changes in BRS and IS suggest a mechanistic link.

Increased glucose production in mice overexpressing human fructose-1,6-bisphosphatase in the liver

Increased endogenous glucose production (EGP) predominantly from the liver is a characteristic feature of type 2 diabetes, which positively correlates with fasting hyperglycemia. Gluconeogenesis is the biochemical pathway shown to significantly contribute to increased EGP in diabetes. Fructose-1,6-bisphosphatase (FBPase) is a regulated enzyme in gluconeogenesis that is increased in animal models of obesity and insulin resistance. However, whether a specific increase in liver FBPase can result in increased EGP has not been shown. The objective of this study was to determine the role of upregulated liver FBPase in glucose homeostasis. To achieve this goal, we generated human liver FBPase transgenic mice under the control of the transthyretin promoter, using insulator sequences to flank the transgene and protect it from site-of-integration effects. This resulted in a liver-specific model, as transgene expression was not detected in other tissues. Mice were studied under the following conditions: 1) at two ages (24 wk and 1 yr old), 2) after a 60% high-fat diet, and 3) when bred to homozygosity. Hemizygous transgenic mice had an approximately threefold increase in total liver FBPase mRNA with concomitant increases in FBPase protein and enzyme activity levels. After high-fat feeding, hemizygous transgenics were glucose intolerant compared with negative littermates (P < 0.02). Furthermore, when bred to homozygosity, chow-fed transgenic mice showed a 5.5-fold increase in liver FBPase levels and were glucose intolerant compared with negative littermates, with a significantly higher rate of EGP (P < 0.006). This is the first study to show that FBPase regulates EGP and whole body glucose homeostasis in a liver-specific transgenic model. Our homozygous transgenic model may be useful for testing human FBPase inhibitor compounds with the potential to treat patients with type 2 diabetes.

Suppression of leptin receptor messenger ribonucleic acid and leptin responsiveness in the ventromedial nucleus of the hypothalamus during pregnancy in the rat

Pregnancy in the rat is a state of leptin resistance associated with impaired leptin signal transduction in the hypothalamus. The aim of this study was to determine whether this leptin-resistant state is mediated by a change in the level of leptin receptors in the hypothalamus. Real-time RT-PCR was used to determine levels of mRNA for the various leptin receptor isoforms in a number of microdissected hypothalamic nuclei and the choroid plexus. To investigate the functional activation of the leptin receptor, immunohistochemistry for phosphorylated signal transducer and activator of transcription 3 (pSTAT3) was examined in the arcuate nucleus and the ventromedial nucleus of the hypothalamus (VMH) of fasted diestrous and d-14 pregnant rats after an intracerebroventricular (i.c.v.) injection of either leptin (4 mug) or vehicle. A significant reduction of Ob-Rb mRNA levels was observed in the VMH during pregnancy compared with the nonpregnant controls. Furthermore, in pregnant rats the number of cells positive for leptin-induced pSTAT3 in the VMH was greatly reduced during pregnancy compared with nonpregnant rats. There were no differences in the level of Ob-Rb mRNA or in the number of leptin-induced pSTAT3-positive cells in the arcuate nucleus of nonpregnant and pregnant rats. These data implicate the VMH as a key hypothalamic site involved in pregnancy-induced leptin resistance. There were also reduced levels of mRNA for Ob-Ra, a proposed leptin transporter molecule, in the choroid plexus on d 7 and 21 of pregnancy. Hence, diminished transport of leptin into the brain may also contribute to pregnancy-induced leptin resistance.

Pregnancy impairs the counterregulatory response to insulin-induced hypoglycemia in the dog

The impact of pregnancy on the counterregulatory response to insulin-induced hypoglycemia was examined in six nonpregnant (NP) and six pregnant (P; 3rd trimester) conscious dogs by tracer and arteriovenous difference techniques. After basal sampling, insulin was infused intraportally at 30 pmol.kg(-1).min(-1) for 180 min. Insulin rose from 70 +/- 15 to 1,586 +/- 221 pmol/l and 27 +/- 4 to 1,247 +/- 61 pmol/l in the 3rd h in NP and P, respectively. Arterial glucose fell from 5.9 +/- 0.2 to 2.3 +/- 0.2 mmol/l in P. Glucose was infused in NP to equate the rate of fall of glucose and the steady-state concentrations in the groups (5.9 +/- 0.2 to 2.3 +/- 0.1 mmol/l in NP). Glucagon was 32 +/- 6, 69 +/- 11, and 48 +/- 10 ng/l (basal and 1st and 3rd h) in NP, but the response was attenuated in P (34 +/- 5, 46 +/- 6, 41 +/- 9 ng/l). Cortisol and epinephrine rose similarly in both groups, but norepinephrine rose more in NP (Delta3.01 +/- 0.46 and Delta1.31 +/- 0.13 nmol/l, P < 0.05). Net hepatic glucose output (NHGO; micromol.kg(-1).min(-1)) increased from 10.6 +/- 1.8 to 21.2 +/- 3.3 in NP (3rd h) but did not increase in P (15.1 +/- 1.5 to 15.3 +/- 2.8 micromol.kg(-1).min(-1), P < 0.05 between groups). The glycogenolytic contribution to NHGO in NP increased from 5.8 +/- 0.7 to 10.4 +/- 2.5 micromol.kg(-1).min(-1) by 90 min but steadily declined in P. The increase in glycerol levels and the gluconeogenic contribution to NHGO were 50% less in P than in NP, but ketogenesis did not differ. The glucagon and norepinephrine responses to insulin-induced hypoglycemia are blunted in late pregnancy in the dog, impacting on the magnitude of the metabolic responses to the fall in glucose.

Peripheral insulin resistance develops in transgenic rats overexpressing phosphoenolpyruvate carboxykinase in the kidney

AIMS/HYPOTHESIS

To study the secondary consequences of impaired suppression of endogenous glucose production (EGP) we have created a transgenic rat overexpressing the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) in the kidney. The aim of this study was to determine whether peripheral insulin resistance develops in these transgenic rats.

METHODS

Whole body rate of glucose disappearance (R(d)) and endogenous glucose production were measured basally and during a euglycaemic/hyperinsulinaemic clamp in phosphoenolpyruvate carboxykinase transgenic and control rats using [6-(3)H]-glucose. Glucose uptake into individual tissues was measured in vivo using 2-[1-(14)C]-deoxyglucose.

RESULTS

Phosphoenolpyruvate carboxykinase transgenic rats were heavier and had increased gonadal and infrarenal fat pad weights. Under basal conditions, endogenous glucose production was similar in phosphoenolpyruvate carboxykinase transgenic and control rats (37.4+/-1.1 vs 34.6+/-2.6 micromol/kg/min). Moderate hyperinsulinaemia (810 pmol/l) completely suppressed EGP in control rats (-0.6+/-5.5 micromol/kg/min, p<0.05) while there was no suppression in phosphoenolpyruvate carboxykinase rats (45.2+/-7.9 micromol/kg/min). Basal R(d) was comparable between PEPCK transgenic and control rats (37.4+/-1.1 vs 34.6+/-2.6 micromol/kg/min) but under insulin-stimulated conditions the increase in R(d) was greater in control compared to phosphoenolpyruvate carboxykinase transgenic rats indicative of insulin resistance (73.4+/-11.2 vs 112.0+/-8.0 micromol/kg/min, p<0.05). Basal glucose uptake was reduced in white and brown adipose tissue, heart and soleus while insulin-stimulated transport was reduced in white and brown adipose tissue, white quadriceps, white gastrocnemius and soleus in phosphoenolpyruvate carboxykinase transgenic compared to control rats. The impairment in both white and brown adipose tissue glucose uptake in phosphoenolpyruvate carboxykinase transgenic rats was associated with a decrease in GLUT4 protein content. In contrast, muscle GLUT4 protein, triglyceride and long-chain acylCoA levels were comparable between PEPCK transgenic and control rats.

CONCLUSIONS/INTERPRETATION

A primary defect in suppression of EGP caused adipose tissue and muscle insulin resistance.

A circulatory model for calculating non-steady-state glucose fluxes. Validation and comparison with compartmental models

This study presents a circulatory model of glucose kinetics for application to non-steady-state conditions, examines its ability to predict glucose appearance rates from a simulated oral glucose load, and compares its performance with compartmental models. A glucose tracer bolus was injected intravenously in rats to determine parameters of the circulatory and two-compartment models. A simulated oral glucose tolerance test was performed in another group of rats by infusing intravenously labeled glucose at variable rates. A primed continuous intravenous infusion of a second tracer was given to determine glucose clearance. The circulatory model gave the best estimate of glucose appearance, closely followed by the two-compartment model and a modified Steele one-compartment model with a larger total glucose volume. The standard one-compartment model provided the worst estimate. The average relative errors on the rate of glucose appearance were: circulatory, 10%; two-compartment, 13%; modified one-compartment, 11%; standard one-compartment, 16%. Recovery of the infused glucose dose was 93+/-2, 94+/-2, 92+/-2 and 85+/-2%, respectively. These results show that the circulatory model is an appropriate model for assessing glucose turnover during an oral glucose load.

Effect of fetal hyperinsulinism on oral glucose tolerance test results in patients with gestational diabetes mellitus

OBJECTIVE

This study was undertaken to evaluate the impact of the fetoplacental glucose steal phenomenon on the results of oral glucose tolerance testing in pregnancies complicated by gestational diabetes mellitus with fetal hyperinsulinism.

STUDY DESIGN

This was an analysis of the cases of 34 patients with two consecutive abnormal oral glucose tolerance test results and amniotic fluid insulin measurement before institution of insulin therapy. Patients were divided into groups on the basis of normal versus elevated amniotic fluid insulin concentrations.

RESULTS

Oral glucose tolerance tests were done at a mean (+/-SD) of 24.9 +/- 5.7 and 30.7 +/- 3.2 weeks' gestation, and amniotic fluid insulin measurements were done at 31.1 +/- 3.2 weeks' gestation. In 13 women with gestational diabetes mellitus with normal amniotic fluid insulin concentration, maternal postload blood glucose levels at 1 hour increased by 12 mg/dL (168 vs 180 mg/dL; 9.3 vs 10.0 mmol/L; P = .0006) during the course of 6 weeks. In contrast, in 21 women with gestational diabetes mellitus with elevated amniotic fluid insulin levels (>7 microU/mL; >42 pmol/L), 1-hour postload blood glucose levels decreased by 22 mg/dL (201 vs 179 mg/dL; 11.2 vs 9.9 mmol/L; P = .002) during the same period. The higher the amniotic fluid insulin level, the larger the decrease (R = 0.504; P =.02). Although low amniotic fluid insulin levels were correlated significantly with 1-hour glucose levels of the first and second oral glucose tolerance tests, high insulin levels were no longer correlated with the second oral glucose tolerance test.

CONCLUSION

Exaggerated fetal glucose siphoning may provide misleading oral glucose tolerance test results in pregnancies complicated by fetal hyperinsulinism by blunting maternal postload glucose peaks. Consequently, oral glucose tolerance test results in a pregnancy complicated by gestational diabetes mellitus with a fetus that already has hyperinsulinemia may erroneously be considered normal.

Sir David Cuthbertson Medal Lecture. The impact of dietary protein restriction on insulin secretion and action

The goal of this review is to develop the hypothesis, and review the evidence, that protein restriction, through synergistic effects on multiple organ systems predisposes to loss of normal regulation of fuel homeostasis that plays the central role in the development of type 2 (non-insulin-dependent) diabetes mellitus. The ability of insulin to regulate glucose production and disposal varies between individuals. These differences, together with the various compensatory mechanisms that are invoked to attempt to normalize fuel homeostasis, are of fundamental importance in the development and clinical course of type 2 diabetes mellitus. Protein deprivation impacts on both insulin secretion and insulin action. These effects may persist even when a diet containing adequate protein is presented subsequently. Data are presented that suggest that protein restriction results in an impaired ability of pancreatic beta-cells to compensate adequately for the defect in insulin action in insulin-resistant individuals. This persistent impairment of insulin secretion resulting from protein restriction predisposes to loss of glucoregulatory control and impaired insulin action after the subsequent imposition of a diabetogenic challenge. This inability to maintain the degree of compensatory hyperinsulinaemia necessary to prevent loss of glucose tolerance may have relevance to the increased incidence of diabetes on changing from a nutritionally-poor diet to a Western diet, and to the hypothesis that some cases of type 2 diabetes in adulthood may be related to poor early nutrition.

Antecedent protein restriction exacerbates development of impaired insulin action after high-fat feeding

The study investigated whether a persistent impairment of insulin secretion resulting from mild protein restriction predisposes to loss of glucoregulatory control and impaired insulin action after the subsequent imposition of the diabetogenic challenge of high-fat feeding. Offspring of dams provided with either control (20% protein) diet (C) or an isocaloric restricted (8%) protein diet (PR) were weaned onto the maintenance diet with which their mothers had been provided. At 20 wk of age, protein restriction enhanced glucose tolerance despite impaired insulin secretion and an augmented and sensitized lipolytic response to norepinephrine in adipocytes. C and PR rats were then transferred to a high-fat diet (HF, 19% protein, 22% lipid, 34% carbohydrate) and sampled after 8 wk. These groups are termed C-HF and PR-HF. Glucose tolerance was impaired in PR-HF, but not C-HF, rats. Insulin-stimulated glucose disposal rates were significantly lower (by 30%; P < 0.01) in the PR-HF group than in the C-HF group, and a specific impairment of antilipolytic response of insulin was unmasked in adipocytes from PR-HF, but not C-HF, rats. The study demonstrates that antecedent protein restriction accelerates and augments the development of impaired glucoregulation and insulin resistance after high-fat feeding.

Effects of food restriction on glucose tolerance, insulin secretion, and islet-cell proliferation in pregnant rats

Pregnancy is associated with increased glucose-stimulated insulin secretion and increased pancreatic islet-cell proliferation. In the present study it was investigated whether increased food intake, as occurs during pregnancy, is involved in the regulation of these phenomena. From Day 0 of pregnancy, rats received each day the mean amount of food they consumed daily during the estrous cycle prior to conception. This food restriction regime resulted in lower maternal body weight, and in lower fetal weight on Day 20 of gestation, but did not affect fetal survival. Food-restricted rats showed decreased insulin responses to an i.v. glucose challenge on Day 13, and lower islet-cell replication rates on Day 14 of pregnancy than pregnant rats fed ad lib. Plasma lactogenic activity in food-restricted animals was increased on Days 11 and 13; plasma progesterone levels were unchanged, but plasma leptin concentrations declined progressively during food restriction. Glucose tolerance was normal, suggesting that food restriction improved insulin action. On Day 20 of pregnancy, insulin responses were similar in food restricted and ad lib-fed rats; glucose tolerance was still unchanged. It thus seems that the improved insulin action as present on Day 13 had disappeared on Day 20. Also on Day 20, lactogenic activity as well as progesterone concentrations were similar in food-restricted and ad lib-fed rats. It was concluded that increased food intake plays an important role in the stimulation of islet-cell proliferation and insulin secretion, as well as in the diminished insulin action during the second week of rat pregnancy.

Moderate protein restriction during pregnancy modifies the regulation of triacylglycerol turnover and leads to dysregulation of insulin's anti-lipolytic action

Moderate protein restriction throughout pregnancy in the rat leads to relative hyperlipidaemia and blunted insulin responsiveness of lipid fuel supply, and impairs foetal growth. The present study examined the basis for these changes. Isocaloric 8% (vs 20%) protein diets were provided throughout pregnancy. Rats were sampled at 19-20 days of gestation. Protein restriction enhanced triacylglycerol (TAG) secretion rates (estimated using Triton WR 1339) 1.6-fold (P < 0.05) in the post-absorptive state. Insulin infusion (4.2 mU/kg per min) decreased plasma TAG concentrations by 33% (P < 0.05) and 48% (P < 0.05) in control (C) and protein-restricted (PR) pregnant groups, an effect associated with suppression of TAG secretion by 42% (P < 0.05) and 51% (P < 0.01) respectively, in the C and PR groups. Since TAG concentrations decline more rapidly, while TAG secretion is enhanced, TAG utilisation during hyperinsulinaemia is enhanced in the PR group. We evaluated whether these changes were associated with dysregulation of lipolysis using adipocytes from two abdominal depots (mesenteric and parametrial). Noradrenaline-stimulated glycerol release was enhanced in parametrial adipocytes (by 40%; P < 0.05) from PR pregnant rats. The anti-lipolytic action of insulin at low concentrations (< or = 15 microU/ml) was impaired by protein restriction (adipocytes from both depots). There was no evidence for altered intra-hepatic regulation of fatty acid (FA) disposal at the level of carnitine palmitoyltransferase. Our results demonstrate increased post-absorptive production of non-carbohydrate energy substrates (TAG and FA) as a consequence of mild protein restriction during pregnancy. These adaptations contribute to a homeostatic strategy to reduce the maternal requirement for gluconeogenesis from available amino acids, optimising the foetal protein supply. Protein restriction also enhances TAG turnover during hyperinsulinaemia. This effect is not a consequence of abnormal regulation of hepatic lipid metabolism by insulin.

Glucose turnover and gluconeogenesis in human pregnancy

The rate of appearance (Ra) of glucose in plasma and the contribution of gluconeogenesis were quantified in normal pregnant women early ( approximately 10 wk) and late ( approximately 34 wk) in gestation. Their data were compared with those of normal nonpregnant women. Glucose Ra was measured using the [U-13C]glucose tracer dilution method. Gluconeogenesis was quantified by the appearance of 2H on carbon 5 and 6 of glucose after deuterium labeling of body water pool. Weight-specific glucose Ra was unchanged during pregnancy (nonpregnant, 1.89+/-0.24; first trimester, 2.05+/-0.21; and third trimester 2.17+/-0.28 mg/kg.min, mean+/-SD), while total glucose Ra was significantly increased (early, 133.5+/-7.2; late, 162.6+/-16.4 mg/min; P = 0.005). The fractional contribution of gluconeogenesis via pyruvate measured by 2H enrichment on C-6 of glucose (45-61%), and of total gluconeogenesis quantified from 2H enrichment on C-5 of glucose (i.e. , including glycerol [68-85%]) was not significantly different between pregnant and nonpregnant women. Inasmuch as total glucose Ra was significantly increased, total gluconeogenesis was also increased in pregnancy (early pregnancy, 94.7+/-15.9 mg/min; late pregnancy, 122.7+/-9.3 mg/min; P = 0.003). These data demonstrate the ability of the mother to adapt to the increasing fetal demands for glucose with advancing gestation. The mechanism for this unique quantitative adjustment to the fetal demands remains undefined.

The set point for maternal glucose homeostasis is lowered during late pregnancy in the rat: the role of the islet beta-cell and liver

The aim of this study was to determine the effects of late pregnancy on the ability of insulin to suppress maternal hepatic glucose production in the rat. Unlike in most previous studies, suppression of hepatic glucose production was measured at levels of glycaemia above the relatively hypoglycaemic basal pregnant level. Glucose kinetics were measured using steady-state tracer methodology in chronically catheterised, conscious virgin control and pregnant rats, firstly, during basal and low-dose hyperinsulinaemic euglycaemic clamp conditions and secondly, during a three-step glucose infusion protocol (glucose infusion rates of 0, 60 and 150 mumol.kg-1. min-1). During the clamps, plasma glucose levels were not different (6.1 +/- 0.4 vs 6.5 +/- 0.3 mmol/l, pregnant vs virgin; N.S.), but plasma insulin levels were higher in the pregnant rats (242 +/- 30 vs 154 +/- 18 pmol/l. pregnant vs virgin; p < 0.05) most probably due to stimulated endogenous insulin release in this group. Hepatic glucose production was suppressed from basal levels by 41% in virgin and 90% in pregnant rats. During the glucose infusion studies, at matched insulin levels (147 +/- 10 vs 152 +/- 14 pmol/l), but at plasma glucose levels which were much lower in the pregnant rats (5.5 +/- 0.2 vs 8.4 +/- 0.6 mmol/l, pregnant vs virgin; p < 0.0001), hepatic glucose production was shown to be suppressed by a similar degree in both groups (41 +/- 5 vs 51 +/- 5% from basal, pregnant vs virgin; N.S.). Both the plasma insulin and percentage suppression of hepatic glucose production dose responses to plasma glucose were markedly shifted to the left indicating that the plasma glucose set point is lowered in pregnancy. In conclusion, suppression of hepatic glucose production by insulin is not impaired and the set point for plasma glucose homeostasis is lowered during late pregnancy in the rat.