Reversion of insulin resistance in the rat during late pregnancy by 72-h glucose infusion

Increased Circulating Levels of PCSK9 and Pro-Atherogenic Lipoprotein Profile in Pregnant Women with Maternal Supraphysiological Hypercholesterolemia

Maternal physiological hypercholesterolemia (MPH) occurs during pregnancy to assure fetal development. Some pregnant women develop maternal supraphysiological hypercholesterolemia (MSPH) characterized by increased levels of low-density lipoprotein (LDL). We aim to determine if proprotein convertase subtilisin/kexin type 9 (PCSK9) levels (a protein that regulate the availability of LDL receptor in the cells surface), as well as the composition and function of LDL, are modulated in MSPH women. This study included 122 pregnant women. Maternal total cholesterol (TC), LDL, triglycerides and PCSK9 increased from first (T1) to third trimester (T3) in MPH women. At T3, maternal TC, LDL, PCSK9 and placental abundances of PCSK9 were significantly higher in MPSH compared to MPH. Circulating PCSK9 levels were correlated with LDL at T3. In MSPH women, the levels of lipid peroxidation and oxidized LDL were significantly higher compared to MPH. LDL isolated from MSPH women presented significantly higher triglycerides and ApoB but lower levels of ApoAI compared to MPH. The formation of conjugated dienes was earlier in LDL from MSPH and in endothelial cells incubated with these LDLs; the levels of reactive oxygen species were significantly higher compared to LDL from MPH. We conclude that increased maternal PCSK9 would contribute to the maternal elevated levels of pro-atherogenic LDL in MSPH, which could eventually be related to maternal vascular dysfunction.

Fetal High-Density Lipoproteins: Current Knowledge on Particle Metabolism, Composition and Function in Health and Disease

Cholesterol and other lipids carried by lipoproteins play an indispensable role in fetal development. Recent evidence suggests that maternally derived high-density lipoprotein (HDL) differs from fetal HDL with respect to its proteome, size, and function. Compared to the HDL of adults, fetal HDL is the major carrier of cholesterol and has a unique composition that implies other physiological functions. Fetal HDL is enriched in apolipoprotein E, which binds with high affinity to the low-density lipoprotein receptor. Thus, it appears that a primary function of fetal HDL is the transport of cholesterol to tissues as is accomplished by low-density lipoproteins in adults. The fetal HDL-associated bioactive sphingolipid sphingosine-1-phosphate shows strong vasoprotective effects at the fetoplacental vasculature. Moreover, lipoprotein-associated phospholipase A2 carried by fetal-HDL exerts anti-oxidative and athero-protective functions on the fetoplacental endothelium. Notably, the mass and activity of HDL-associated paraoxonase 1 are about 5-fold lower in the fetus, accompanied by an attenuation of anti-oxidative activity of fetal HDL. Cholesteryl ester transfer protein activity is reduced in fetal circulation despite similar amounts of the enzyme in maternal and fetal serum. This review summarizes the current knowledge on fetal HDL as a potential vasoprotective lipoprotein during fetal development. We also provide an overview of whether and how the protective functionalities of HDL are impaired in pregnancy-related syndromes such as pre-eclampsia or gestational diabetes mellitus.

Angiopoietin-like protein 4 (ANGPTL4) is related to gestational weight gain in pregnant women with obesity

Angiopoietin-like protein 4 (ANGPTL4) is a circulating protein involved in the regulation of adipose tissue metabolism. However, its role in obesity and pregnancy is unknown. To evaluate the relationship between gestational weight gain (GWG) and circulating concentrations of ANGPTL4 in pregnant women with overweight and obesity, weight gain and fasting maternal blood samples of thirty-one pregnant women was drawn at 15, 24 and 32 weeks of gestation. ANGPTL4 concentrations continuously rose throughout gestation, whereas VEGF and leptin did not show the same trend. NEFA and glycerol concentrations remained stable during pregnancy. In contrast, total concentrations of saturated, monounsaturated and n-6 fatty acids, but not n-3 fatty acids, increased with pregnancy. In multiple regression analysis, the increase in plasma ANGPTL4 and decrease in linoleic acid concentrations were the most significant predictors of GWG, although only ANGPTL4 was significantly associated with the weight gain from early pregnancy (area under the ROC curve was 0.80 p < 0.01(95% CI 0.61-0.99)). In conclusion, in pregnant women with overweight and obesity, an increase in plasma ANGPTL4 concentrations throughout pregnancy is positively associated with GWG and could be used as an early marker of increased susceptibility to excess gestational weight gain.

Implications of Lipids in Neonatal Body Weight and Fat Mass in Gestational Diabetic Mothers and Non-Diabetic Controls

PURPOSE OF REVIEW

Maternal lipid metabolism greatly changes during pregnancy and we review in this article how they influence fetal adiposity and growth under non-diabetic and gestational diabetic conditions.

RECENT FINDINGS

In pregnant women without diabetes (control), maternal glycemia correlates with neonatal glycemia, neonatal body weight and fat mass. In pregnant women with gestational diabetes mellitus (GDM), maternal glucose correlates with neither neonatal glycemia, neonatal birth weight nor fat mass, but maternal triacylglycerols (TAG), non-esterified fatty acids (NEFA) and glycerol do correlate with birth weight and neonatal adiposity. The proportions of maternal plasma arachidonic (AA) and docosahexaenoic (DHA) acids decrease from the first to the third trimester of pregnancy, and at term these long-chain polyunsaturated fatty acids are higher in cord blood plasma than in mothers, indicating efficient placental transfer. In control or pregnant women with GDM at term, the maternal concentration of individual fatty acids does not correlate with neonatal body weight or fat mass, but cord blood fatty acid levels correlate with birth weight and neonatal adiposity-positively in controls, but negatively in GDM. The proportion of AA and DHA in umbilical artery plasma in GDM is lower than in controls but not in umbilical vein plasma. Therefore, an increased utilization of those two fatty acids by fetal tissues, rather than impaired placental transfer, is responsible for their smaller proportion in plasma of GDM newborns. In control pregnant women, maternal glycemia controls neonatal body weight and fat mass, whereas in mothers with GDM-even with good glycemic control-maternal lipids and their greater utilization by the fetus play a critical role in neonatal body weight and fat mass. We propose that altered lipid metabolism rather than hyperglycemia constitutes a risk for macrosomia in GDM.

Maternal adipose tissue becomes a source of fatty acids for the fetus in fasted pregnant rats given diets with different fatty acid compositions

PURPOSE

The utilization of long-chain polyunsaturated fatty acids (LCPUFA) by the fetus may exceed its capacity to synthesize them from essential fatty acids, so they have to come from the mother. Since adipose tissue lipolytic activity is greatly accelerated under fasting conditions during late pregnancy, the aim was to determine how 24 h fasting in late pregnant rats given diets with different fatty acid compositions affects maternal and fetal tissue fatty acid profiles.

METHODS

Pregnant Sprague-Dawley rats were given isoenergetic diets containing 10% palm-, sunflower-, olive- or fish-oil. Half the rats were fasted from day 19 of pregnancy and all were studied on day 20. Triacylglycerols (TAG), glycerol and non-esterified fatty acids (NEFA) were analyzed by enzymatic methods and fatty acid profiles were analyzed by gas chromatography.

RESULTS

Fasting caused increments in maternal plasma NEFA, glycerol and TAG, indicating increased adipose tissue lipolytic activity. Maternal adipose fatty acid profiles paralleled the respective diets and, with the exception of animals on the olive oil diet, maternal fasting increased the plasma concentration of most fatty acids. This maintains the availability of LCPUFA to the fetus during brain development.

CONCLUSIONS

The results show the major role played by maternal adipose tissue in the storage of dietary fatty acids during pregnancy, thus ensuring adequate availability of LCPUFA to the fetus during late pregnancy, even when food supply is restricted.

Maternal fuels and metabolic measures during pregnancy and neonatal body composition: the healthy start study

CONTEXT

The impact of specific maternal fuels and metabolic measures during early and late gestation on neonatal body composition is not well defined.

OBJECTIVE

To determine how circulating maternal glucose, lipids, and insulin resistance in the first and second halves of pregnancy influence neonatal body composition.

DESIGN

A prospective pre-birth cohort enrolling pregnant women, the Healthy Start Study, was conducted, in which fasting maternal serum samples were collected twice during pregnancy to measure glucose, insulin, hemoglobin A1c, triglyceride, total cholesterol, high-density lipoprotein, and free fatty acids. Neonatal body composition was measured with air displacement plethysmography.

SETTING

An observational epidemiology study of pregnant women attending obstetric clinics at the University of Colorado, Anschutz Medical Center.

PARTICIPANTS

This analysis includes 804 maternal-neonate pairs.

RESULTS

A strong positive linear relationship between maternal estimated insulin resistance (homeostasis model of assessment for insulin resistance) in the first half of pregnancy and neonatal fat mass (FM) and FM percentage (FM%) was detected, independent of prepregnancy body mass index (BMI). In the second half of pregnancy, positive linear relationships between maternal glucose levels and offspring FM and FM% were observed, independent of prepregnancy BMI. An inverse relationship was detected between high-density lipoprotein in the first half of pregnancy and FM, independent of prepregnancy BMI. Free fatty acid levels in the second half of pregnancy were positively associated with higher birth weight, independent of prepregnancy BMI.

CONCLUSION

Maternal insulin resistance in the first half of pregnancy is highly predictive of neonatal FM%, whereas maternal glycemia, even within the normal range, is an important driver of neonatal adiposity in later pregnancy, independent of prepregnancy BMI. Our data provide additional insights on potential maternal factors responsible for fetal fat accretion and early development of adiposity.

Implication of low level inflammation in the insulin resistance of adipose tissue at late pregnancy

Insulin resistance is a characteristic of late pregnancy, and adipose tissue is one of the tissues that most actively contributes to the reduced maternal insulin sensitivity. There is evidence that pregnancy is a condition of moderate inflammation, although the physiological role of this low-grade inflammation remains unclear. The present study was designed to validate whether low-grade inflammation plays a role in the development of insulin resistance in adipose tissue during late pregnancy. To this end, we analyzed proinflammatory adipokines and kinases in lumbar adipose tissue of nonpregnant and late pregnant rats at d 18 and 20 of gestation. We found that circulating and tissue levels of adipokines, such as IL-1β, plasminogen activator inhibitor-1, and TNF-α, were increased at late pregnancy, which correlated with insulin resistance. The observed increase in adipokines coincided with an enhanced activation of p38 MAPK in adipose tissue. Treatment of pregnant rats with the p38 MAPK inhibitor SB 202190 increased insulin-stimulated tyrosine phosphorylation of the insulin receptor (IR) and IR substrate-1 in adipose tissue, which was paralleled by a reduction of IR substrate-1 serine phosphorylation and an enhancement of the metabolic actions of insulin. These results indicate that activation of p38 MAPK in adipose tissue contributes to adipose tissue insulin resistance at late pregnancy. Furthermore, the results of the present study support the hypothesis that physiological low-grade inflammation in the maternal organism is relevant to the development of pregnancy-associated insulin resistance.

Enhanced utilization of glycerol for glyceride synthesis in isolated adipocytes from early pregnant rats

Adipose tissue normally has low glycerol kinase activity, but its expression is enhanced under conditions of augmented insulin sensitivity and/or obesity. Since these conditions occur during early pregnancy, the comparative utilization of glucose or glycerol by isolated adipocytes from rats at 0, 7, 14, or 20 days of pregnancy was studied. Incubations were carried out in the presence of [U(14)C]-glucose or -glycerol in medium supplemented or not with 5 mM glucose and 100 nM insulin. The conversion of glucose into esterified fatty acids and glyceride glycerol was greatest in adipocytes from 7-day pregnant rats, the effect being further enhanced by insulin. Both the amount of aquoporin 7 and the in vitro conversion of glycerol into glyceride glycerol were greatest in adipocytes of 7-day pregnant rats, the later being unaltered by insulin. In the presence of glucose, the overall glycerol utilization was lower than in its absence and glycerol conversion into glyceride glycerol was further decreased by insulin, the effect only being significant in adipocytes from 7-day pregnant rats. It is proposed that the enhanced utilization of glycerol for glyceride glycerol synthesis in adipose tissue contributes to the net accumulation of fat depots that normally takes place in early pregnancy.

Restrição protéica na prenhez: efeitos relacionados ao metabolismo materno

Foram avaliadas as alterações no metabolismo materno durante a prenhez em ratas Wistar, prenhes e não-prenhes, submetidas à restrição protéica, que receberam dietas isocalóricas (15,74 kJ/g), controle ou hipoprotéica (17% versus 6%), distribuídas em quatro grupos (n = 7), quais sejam: controle não-prenhe (CNP) e prenhe (CP) e hipoprotéico não-prenhe (HNP) e prenhe (HP), do 1º ao 18º dia de prenhez. Parâmetros bioquímicos, hormonais e relacionados à síntese de lipídios foram considerados. Utilizou-se ANOVA a duas vias seguido de teste Tukey-HSD e teste t de Student, significância de p < 0,05. A restrição protéica elevou a síntese de lipídios e a atividade da enzima málica (EM) no fígado (FIG) e reduziu a massa (%) e a razão lipí+dio/glicogênio nesse tecido, bem como reduziu a ingestão protéica (total e %), o conteúdo (%) de lipídios na glândula mamária (GMA), as proteínas e a albumina séricas, com consequente redução nas massas da placenta e fetos. A prenhez reduziu a proteinemia, a albuminemia, a síntese de lipídios, a atividade da EM, os lipídios e o glicogênio no FIG. Mas elevou a massa corporal final, a massa (%) do tecido adiposo gonadal (GON), do FIG e da GMA, e reduziu a massa (%) da carcaça (CARC), a síntese e o conteúdo de lipídios no GON e, na GMA, o conteúdo de lipídios. A insulinemia elevou-se na prenhez, com glicemia reduzida, caracterizando resistência hormonal. A leptina e a prolactina também se elevaram na prenhez, sendo o aumento maior no HP. A restrição protéica na prenhez modificou o metabolismo materno, alterando a síntese de lipídios no FIG e o perfil hormonal, além de reduzir a massa da placenta e dos fetos.

Validation of simple indexes to assess insulin sensitivity during pregnancy in Wistar and Sprague-Dawley rats

Insulin resistance plays a role in the pathogenesis of diabetes, including gestational diabetes. The glucose clamp is considered the gold standard for determining in vivo insulin sensitivity, both in human and in animal models. However, the clamp is laborious, time consuming and, in animals, requires anesthesia and collection of multiple blood samples. In human studies, a number of simple indexes, derived from fasting glucose and insulin levels, have been obtained and validated against the glucose clamp. However, these indexes have not been validated in rats and their accuracy in predicting altered insulin sensitivity remains to be established. In the present study, we have evaluated whether indirect estimates based on fasting glucose and insulin levels are valid predictors of insulin sensitivity in nonpregnant and 20-day-pregnant Wistar and Sprague-Dawley rats. We have analyzed the homeostasis model assessment of insulin resistance (HOMA-IR), the quantitative insulin sensitivity check index (QUICKI), and the fasting glucose-to-insulin ratio (FGIR) by comparing them with the insulin sensitivity (SI(Clamp)) values obtained during the hyperinsulinemic-isoglycemic clamp. We have performed a calibration analysis to evaluate the ability of these indexes to accurately predict insulin sensitivity as determined by the reference glucose clamp. Finally, to assess the reliability of these indexes for the identification of animals with impaired insulin sensitivity, performance of the indexes was analyzed by receiver operating characteristic (ROC) curves in Wistar and Sprague-Dawley rats. We found that HOMA-IR, QUICKI, and FGIR correlated significantly with SI(Clamp), exhibited good sensitivity and specificity, accurately predicted SI(Clamp), and yielded lower insulin sensitivity in pregnant than in nonpregnant rats. Together, our data demonstrate that these indexes provide an easy and accurate measure of insulin sensitivity during pregnancy in the rat.

Triglyceridemia and peroxisome proliferator- activated receptor-α expression are not connected in fenofibrate-treated pregnant rats

To investigate the response to fenofibrate in pregnant rats, 0 mg, 100 mg or 200 mg of fenofibrate per kilogram body weight oral doses were given twice a day from day 16 of gestation and studied at day 20. Virgin rats were studied in parallel. Whereas in pregnant rats plasma triglycerides significantly increased, in virgin rats, fenofibrate decreased plasma triglycerides which accumulated in liver. Fenofibrate faithfully modulated the hepatic expression of PPARalpha responsive genes. Fenofibrate increased mRNA contents corresponding to both acyl-CoA oxidase, carnitine palmitoyltransferase (CPT), and peroxisome proliferator-activated receptor alpha (PPAR), and lowered mRNA amounts of apolipoproteins B and C-III, both in virgin and pregnant rats. However, genes related to hepatic lipogenesis, such as PPARy and stearoyl-CoA desaturase (SCD), showed an augmented expression by fenofibrate in virgin rats, but not in pregnant animals. We propose that the opposite effects of fenofibrate treatment in virgin and pregnant rats are a consequence of the enhanced capability for VLDL-triglyceride production in the latter, further promoted by the elevated amount of free fatty acids (FFA), which reach the liver in treated pregnant rats and were not sufficiently oxidized and/or stored, and therefore would have to be canalized as triglycerides to the plasma. Thus, the present study shows how fenofibrate, in spite of efficiently exerting its expected molecular effects in the liver (i.e., to induce fatty acid and lipoprotein catabolism, and to reduce TG-rich lipoprotein secretion), was unable to reverse the typical hypertriglyceridaemia of gestation.

Fat accumulation in the rat during early pregnancy is modulated by enhanced insulin responsiveness

Insulin sensitivity has been implicated in the variation of fat accumulation in early gestation by as-yet-unknown mechanisms. In the present study, we analyzed the insulin sensitivity of lipolysis and lipogenesis in lumbar adipocytes from rats at 0, 7, 14, and 20 days of gestation. In adipocytes of 7-day pregnant rats, we found a twofold decrease in both beta-agonist (isoproterenol and BRL-37344)-stimulated lipolysis and beta3-adrenoceptor protein but not in lipolysis initiated by forskolin or isobutylmethylxanthine, suggesting a modification of the lipolytic pathway at the receptor level. Whereas adipocytes from 7-day pregnant rats showed a twofold increase in fatty acid synthesis from glucose, those from 20-day pregnant animals displayed a decreased lipogenic activity. Insulin responsiveness of the lipolytic and lipogenic pathways was analyzed by dose-response experiments, giving evidence for the involvement of improved insulin responsiveness in the enhanced lipogenic and reduced lipolytic activities of adipocytes in early pregnancy. In contrast, insulin resistance is responsible for lower antilipolytic and lipogenic actions of insulin in late pregnant animals. In conclusion, the present study shows that enhanced adipose tissue insulin responsiveness during early pregnancy contributes to maternal fat accumulation, whereas decreased insulin responsiveness during late gestation modulates fat breakdown.

Lipid metabolism in pregnancy and its consequences in the fetus and newborn

During early pregnancy there is an increase in body fat accumulation, associated with both hyperphagia and increased lipogenesis. During late pregnancy there is an accelerated breakdown of fat depots, which plays a key role in fetal development. Besides using placental transferred fatty acids, the fetus benefits from two other products: glycerol and ketone bodies. Although glycerol crosses the placenta in small proportions, it is a preferential substrate for maternal gluconeogenesis, and maternal glucose is quantitatively the main substrate crossing the placenta. Enhanced ketogenesis under fasting conditions and the easy transfer of ketones to the fetus allow maternal ketone bodies to reach the fetus, where they can be used as fuels for oxidative metabolism as well as lipogenic substrates. Although maternal cholesterol is an important source of cholesterol for the fetus during early gestation, its importance becomes minimal during late pregnancy, owing to the high capacity of fetal tissues to synthesize cholesterol. Maternal hypertriglyceridemia is a characteristic feature during pregnancy and corresponds to an accumulation of triglycerides not only in very low-density lipoprotein but also in low- and high-density lipoprotein. Although triglycerides do not cross the placental barrier, the presence of lipoprotein receptors in the placenta, together with lipoprotein lipase, phospholipase A2, and intracellular lipase activities, allows the release to the fetus of polyunsaturated fatty acids transported as triglycerides in maternal plasma lipoproteins. Normal fetal development needs the availability of both essential fatty acids and long chain polyunsaturated fatty acids, and the nutritional status of the mother during gestation has been related to fetal growth. However, excessive intake of certain long chain fatty acids may cause both declines in arachidonic acid and enhanced lipid peroxidation, reducing antioxidant capacity.

Differential metabolic response to 48 h food deprivation at different periods of pregnancy in the rat

Since during pregnancy the mother switches from an anabolic to a catabolic condition, the present study was addressed to determine the effect of 48 h food deprivation on days 7, 14 and 20 of pregnancy in the rat as compared to age matched virgin controls. Body weight, free of conceptus, decreased with food deprivation more in pregnant than in virgin rats, with fetal weight (day 20) also diminishing with maternal starvation. The decline of plasma glucose with food deprivation was greatest in 20 day pregnant rats. Insulin was highest in fed 14 day pregnant rats, and declined with food deprivation in all the groups, the effect being not significant in 7-day pregnant rats. Food deprivation increased plasma glycerol only in virgin and 20 day pregnant rats. Plasma NEFA and 3-hydroxybutyrate increased with food deprivation in all groups, the effect being highest in 20 day pregnant rats. Food deprivation decreased plasma triacylglycerols in 14 day pregnant rats but increased in 20 day pregnant rats. In 20-day fetuses, plasma levels of glucose, NEFA and triacylglycerols were lower than in their mothers when fed, and food deprivation caused a further decline in plasma glucose, whereas both NEFA and 3-hydroxybutyrate increased. Liver triacylglycerols concentration did not differ among the groups when fed, whereas food deprivation caused an increase in all pregnant rats and fetuses, the effect being highest in 20-day pregnant rats. Lipoprotein lipase (LPL) activity in adipose tissue was lower in 20 day pregnant rats than in any of the other groups when fed, and it decreased in all the groups with food deprivation, whereas in liver it was very low in all groups when fed and increased with food deprivation only in 20 day pregnant rats. A significant increase in liver LPL was found with food deprivation in 20 day fetuses, reaching higher values than their mothers. Thus, the response to food deprivation varies with the time of pregnancy, being lowest at mid pregnancy and greatest at late pregnancy, and although fetuses respond in the same direction as their mothers, they show a specific response in liver LPL activity.

Implications of dietary fatty acids during pregnancy on placental, fetal and postnatal development--a review

During pregnancy, the mother adapts her metabolism to support the continuous draining of substrates by the fetus. Her increase in net body weight (free of the conceptus) corresponds to the accumulation of fat depots during the first two-thirds of gestation, switching to an accelerated breakdown of these during the last trimester. Under fasting conditions, adipose tissue lipolytic activity is highly enhanced, and its products, free fatty acids (FFA) and glycerol, are mainly driven to maternal liver, where FFA are converted to ketone bodies and glycerol to glucose, which easily cross the placenta and sustain fetal metabolism. Lipolytic products reaching maternal liver are also used for triglyceride synthesis that are released in turn to the circulation, where together with an enhanced transfer of triglycerides among the different lipoprotein fractions, and a decrease in extrahepatic lipoprotein lipase activity, increase the content of triglycerides in all the lipoprotein fractions. Long chain polyunsaturated fatty acids (LCPUFA) circulate in maternal plasma associated to lipoprotein triglycerides, and in a minor proportion in the form of FFA. Despite the lack of a direct placental transfer of triglycerides, diffusion of their fatty acids to the fetus is ensured by means of lipoprotein receptors, lipoprotein lipase activity and intracellular lipase activities in the placenta. Maternal plasma FFA are also an important source of LCPUFA to the fetus, and their placental uptake occurs via a selective process of facilitated membrane translocation involving a plasma membrane fatty acid-binding protein. This mechanism together with a selective cellular metabolism determine the actual rate of placental transfer and its selectivity, resulting even in an enrichment of certain LCPUFA in fetal circulation as compared to maternal. The degree to which the fetus is capable of fatty acid desaturation and elongation is not clear, although both term and preterm infants can synthesize LCPUFA from parental essential fatty acids. Nutritional status of the mother during gestation is related to fetal growth, and excessive dietary intake of certain LCPUFA has inhibitory effects on Delta-5- and Delta-6-desaturases. This inhibition causes major declines in arachidonic acid levels, as directly found in pregnant and lactating rats fed a fish oil-rich diet as compared to olive oil. An excess in dietary PUFA may also enhance peroxidation and reduce antioxidant capacity. Thus, since benefit to risks of modifying maternal fat intake in pregnancy and lactation are not yet completely established, additional studies are needed before recommendations to increase LCPUFA intake in pregnancy are made.

Lipid metabolism in the fetus and the newborn

During late gestation, although maternal adipose tissue lipolytic activity becomes enhanced, lipolytic products cross the placenta with difficulty. Under fasting conditions, free fatty acids (FFA) are used for ketogenesis by the mother, and ketone bodies are used as fuels and lipogenic substrates by the fetus. Maternal glycerol is preferentially used for glucose synthesis, saving other gluconeogenic substrates, like amino acids, for fetal growth. Placental transfer of triglycerides is null, but essential fatty acids derived from maternal diet, which are transported as triglycerides in lipoproteins, become available to the fetus owing to the presence of both lipoprotein receptors and lipase activities in the placenta. Diabetes in pregnancy promotes lipid transfer to the fetus by increasing the maternal-fetal gradient, which may contribute to an increase in body fat mass in newborns of diabetic women. Deposition of fat stores in the fetus is very low in the rat but high in humans, where body fat accretion occurs essentially during the last trimester of intra-uterine life. This is sustained by the intense placental transfer of glucose and by its use as a lipogenic substrate, as well as by the placental transfer of fatty acids and to their low oxidation activity. During the perinatal period an active ketonemia develops, which is maintained in the suckling newborn by several factors: (i) the high-fat and low-carbohydrate content in milk, (ii) the enhanced lipolytic activity occurring during the first few hours of life, and (iii) both the uptake of circulating triglycerides by the liver due to the induction of lipoprotein lipase (LPL) activity in this organ, and the presence of ketogenic activity in the intestinal mucose. Changes in LPL activity, lipogenesis and lipolysis contribute to the sequential steps of adipocyte hyperplasia and hypertrophia occurring during the extra-uterine white adipose tissue development in rat, and this may be used as a model to extrapolate the intra-uterine adipose tissue development in other species, including humans.

Aerobic exercise during pregnancy reverts maternal insulin resistance in rats

PURPOSE AND METHODS

To determine whether pregnancy modifies the effect of aerobic exercise on insulin responsiveness, female rats were mated or kept nonpregnant and exercised or not on a treadmill (10 degrees slope, 20 m.min-1) 5 d.wk-1 during a 20-min period that was increased progressively up to 70 min on the 19th d. On day 20, a hyperinsulinemic euglycemic clamp was performed with 0.8 IU insulin.h-1.kg-1 under conscious conditions.

RESULTS

Food intake and body weight, circulating lactic acid, glucose, and insulin as well as fetal body weight and number were unaffected by the exercise protocol. The rate of glucose infusion required to maintain basal glucose levels during the clamp was similar in exercised and nonexercised virgin rats and significantly lower in pregnant than in virgin nonexercised rats. However, in exercised pregnant rats the glucose infusion rate was almost as high as in the exercised virgin rats.

CONCLUSIONS

The results show that although our aerobic exercise protocol does not affect insulin responsiveness in nonpregnant rats, it completely reverts the insulin resistance present in late pregnant rats.

Impaired glucose homeostasis in insulin-like growth factor binding protein-1 transgenic mice

Transgenic mice that overexpressed IGFBP-1 are hyperinsulinemic in the first week of life and gradually develop fasting hyperglycemia. In adult transgenic mice, the hypoglycemic response to IGF-I but not insulin or des (1-3) IGF-I was attenuated (P < 0.05) compared with wild-type mice. Furthermore, in isolated adipocytes from transgenic mice, the stimulatory effect of IGF-I but not insulin on 2-deoxy-[3H]-glucose uptake was reduced (P < 0.02). In contrast, in isolated soleus muscle, the effects of both IGF-I and insulin on 2-deoxy-3H-glucose uptake and on [3H]-glucose incorporation into glycogen were significantly reduced compared to wild-type mice. The decline in specific activity of the 2-deoxy-3H-glucose, a measure of glucose appearance in the circulation, was more marked in transgenic animals (P < 0.05). In addition, tissue uptake of glucose was significantly higher in diaphragm, heart, intestine, liver, soleus muscle, and adipose tissue from fasting transgenic mice. Plasma concentrations of alanine, lysine, and methionine were also elevated in transgenic mice. These data suggest that overexpression of IGFBP-1 attenuates the hypoglycemic effect of endogenous IGF-I, which is initially compensated for by enhanced pancreatic insulin production. However, in adult mice pancreatic insulin content is reduced, insulin resistance is demonstrable in skeletal muscle and fasting hyperglycemia develops.