Increased insulin sensitivity and maintenance of glucose utilization rates in fetal sheep with placental insufficiency and intrauterine growth restriction

In this study we determined body weight-specific fetal (umbilical) glucose uptake (UGU), utilization (GUR), and production rates (GPR) and insulin action in intrauterine growth-restricted (IUGR) fetal sheep. During basal conditions, UGU from the placenta was 33% lower in IUGR fetuses, but GUR was not different between IUGR and control fetuses. The difference between glucose utilization and UGU rates in the IUGR fetuses demonstrated the presence and rate of fetal GPR (41% of GUR). The mRNA concentrations of the gluconeogenic enzymes glucose-6-phophatase and PEPCK were higher in the livers of IUGR fetuses, perhaps in response to CREB activation, as phosphorylated CREB/total CREB was increased 4.2-fold. A hyperglycemic clamp resulted in similar rates of glucose uptake and utilization in IUGR and control fetuses. The nearly identical GURs in IUGR and control fetuses at both basal and high glucose concentrations occurred at mean plasma insulin concentrations in the IUGR fetuses that were approximately 70% lower than controls, indicating increased insulin sensitivity. Furthermore, under basal conditions, hepatic glycogen content was similar, skeletal muscle glycogen was increased 2.2-fold, the fraction of fetal GUR that was oxidized was 32% lower, and GLUT1 and GLUT4 concentrations in liver and skeletal muscle were the same in IUGR fetuses compared with controls. These results indicate that insulin-responsive fetal tissues (liver and skeletal muscle) adapt to the hypoglycemic-hypoinsulinemic IUGR environment with mechanisms that promote glucose utilization, particularly for glucose storage, including increased insulin action, glucose production, shunting of glucose utilization to glycogen production, and maintenance of glucose transporter concentrations.     

Postnatal pancreatic islet β cell function and insulin sensitivity at different stages of lifetime in rats born with intrauterine growth retardation

Epidemiological studies have linked intrauterine growth retardation (IUGR) to the metabolic diseases, consisting of insulin resistance, type 2 diabetes, obesity and coronary artery disease, during adult life. To determine the internal relationship between IUGR and islet β cell function and insulin sensitivity, we established the IUGR model by maternal nutrition restriction during mid- to late-gestation. Glucose tolerance test and insulin tolerance test (ITT) in vivo and glucose stimulated insulin secretion (GSIS) test in vitro were performed at different stages in IUGR and normal groups. Body weight, pancreas weight and pancreas/body weight of IUGR rats were much lower than those in normal group before 3 weeks of age. While the growth of IUGR rats accelerated after 3 weeks, pancreas weight and pancreas/body weight remained lower till 15 weeks of age. In the newborns, the fasting glucose and insulin levels of IUGR rats were both lower than those of controls, whereas glucose levels at 120 and 180 min after glucose load were significantly higher in IUGR group. Between 3 and 15 weeks of age, both the fasting glucose and insulin levels were elevated and the glucose tolerance was impaired with time in IUGR rats. At age 15 weeks, the area under curve of insulin (AUCi) after glucose load in IUGR rats elevated markedly. Meanwhile, the stimulating index of islets in IUGR group during GSIS test at age 15 weeks was significantly lower than that of controls. ITT showed no significant difference in two groups before 7 weeks of age. However, in 15-week-old IUGR rats, there was a markedly blunted glycemic response to insulin load compared with normal group. These findings demonstrate that IUGR rats had both impaired pancreatic development and deteriorated glucose tolerance and insulin sensitivity, which would be the internal causes why they were prone to develop type 2 diabetes.     

Sensitivity to metabolic signals in late-gestation growth-restricted fetuses from rapidly growing adolescent sheep

Fetal sensitivity to insulin and glucose was investigated during fetal hyperinsulinemic-euglycemic (HI-euG, n = 18) and hyperglycemic-euinsulinemic (HG-euI, n = 12) clamps. Singleton bearing adolescent ewes were fed high (H) or control (C) nutrient intakes to induce compromised or normal placental/fetal size, respectively. Catheters were inserted in the umbilical vein (v), fetal artery, (a) and veins, and studies were conducted between day 126 and 133 of gestation. Umbilical blood flow (UmBF) was determined by the steady-state transplacental diffusion technique using (3)H(2)O, and glucose fluxes were quantified by the Fick principle. For the HI-euG study, fetal glucose utilization was measured at spontaneously occurring fetal insulin concentrations and two additional higher levels, whereas fetal glucose was clamped at the initial baseline level. For the HG-euI study, fetal insulin was suppressed by somatostatin infusion, and fetal glucose utilization was determined at baseline (before somatostatin) glucose concentrations, and at 150 and 200% of this value. Placentome weight (219 vs. 395 g), fetal weight (2,965 vs. 4,373 g), and UmBF (519 vs. 794 ml/min) were lower (P < 0.001) in H than in C groups. Relative to control fetuses, glucose extraction (G[v - a]/G[v] x 100) in the nonperturbed state was higher (21.7 vs. 15.9%) in growth-restricted fetuses despite lower glucose (0.78 vs. 1.05 micromol/ml) and insulin (8.5 vs. 16.9 microU/ml) concentrations (all P < 0.001). During the HI-euG study, total fetal glucose utilization rate increased in response to higher insulin concentrations (65 and 64% in H and C groups). Similarly during the HG-euI study, a twofold increase in glucose supply increased fetal glucose utilization by 41 and 44% in H and C groups, respectively. Throughout both studies, absolute total fetal glucose utilization rates were reduced in H vs. C groups (P < 0.01) but were similar when expressed per kilogram fetus (HI-euG: 34.7, 49.5, and 57.5 in H vs. 34.7, 51.2, and 56.1 micromol.min(-1).kg(-1) in C, HG-euI: 28.7, 35.7, and 40.8 in H vs. 32.9, 34.5, and 43.8 micromol.min(-1).kg(-1) in C). These normal body weight-specific metabolic responses to short-term experimental increases in plasma insulin and glucose in response to chronic IUGR indicate maintained mechanisms of insulin action and glucose uptake/utilization capacity, which, if persistent, might predispose such IUGR offspring to excessive energy deposition in later life.     

Myocardial macronutrient transporter adaptations in the adult pregestational female intrauterine and postnatal growth-restricted offspring

Associations between exponential childhood growth superimposed on low birth weight and adult onset cardiovascular disease with glucose intolerance/type 2 diabetes mellitus exist in epidemiological investigations. To determine the metabolic adaptations that guard against myocardial failure on subsequent exposure to hypoxia, we compared with controls (CON), the effect of intrauterine (IUGR), postnatal (PNGR), and intrauterine and postnatal (IPGR) calorie and growth restriction (n = 6/group) on myocardial macronutrient transporter (fatty acid and glucose) -mediated uptake in pregestational young female adult rat offspring. A higher myocardial FAT/CD36 protein expression in IUGR, PNGR, and IPGR, with higher FATP1 in IUGR, FATP6 in PNGR, FABP-c in PNGR and IPGR, and no change in GLUT4 of all groups was observed. These adaptive macronutrient transporter protein changes were associated with no change in myocardial [(3)H]bromopalmitate accumulation but a diminution in 2-deoxy-[(14)C]glucose uptake. Examination of the sarcolemmal subfraction revealed higher basal concentrations of FAT/CD36 in PNGR and FATP1 and GLUT4 in IUGR, PNGR, and IPGR vs. CON. Exogenous insulin uniformly further enhanced sarcolemmal association of these macronutrient transporter proteins above that of basal, with the exception of insulin resistance of FATP1 and GLUT4 in IUGR and FAT/CD36 in PNGR. The basal sarcolemmal macronutrient transporter adaptations proved protective against subsequent chronic hypoxic exposure (7 days) only in IUGR and PNGR, with notable deterioration in IPGR and CON of the echocardiographic ejection fraction. We conclude that the IUGR and PNGR pregestational adult female offspring displayed a resistance to insulin-induced translocation of FATP1, GLUT4, or FAT/CD36 to the myocardial sarcolemma due to preexistent higher basal concentrations. This basal adaptation of myocardial macronutrient transporters ensured adequate fatty acid uptake, thereby proving protective against chronic hypoxia-induced myocardial compromise.     

Prolonged infusion of amino acids increases leucine oxidation in fetal sheep

Maternal high-protein supplements designed to increase birth weight have not been successful. We recently showed that maternal amino acid infusion into pregnant sheep resulted in competitive inhibition of amino acid transport across the placenta and did not increase fetal protein accretion rates. To bypass placental transport, singleton fetal sheep were intravenously infused with an amino acid mixture (AA, n = 8) or saline [control (Con), n = 10] for ～12 days during late gestation. Fetal leucine oxidation rate increased in the AA group (3.1 ± 0.5 vs. 1.4 ± 0.6 μmol·min(-1)·kg(-1), P < 0.05). Fetal protein accretion (2.6 ± 0.5 and 2.2 ± 0.6 μmol·min(-1)·kg(-1) in AA and Con, respectively), synthesis (6.2 ± 0.8 and 7.0 ± 0.9 μmol·min(-1)·kg(-1) in AA and Con, respectively), and degradation (3.6 ± 0.6 and 4.5 ± 1.0 μmol·min(-1)·kg(-1) in AA and Con, respectively) rates were similar between groups. Net fetal glucose uptake decreased in the AA group (2.8 ± 0.4 vs. 3.9 ± 0.1 mg·kg(-1)·min(-1), P < 0.05). The glucose-O(2) quotient also decreased over time in the AA group (P < 0.05). Fetal insulin and IGF-I concentrations did not change. Fetal glucagon increased in the AA group (119 ± 24 vs. 59 ± 9 pg/ml, P < 0.05), and norepinephrine (NE) also tended to increase in the AA group (785 ± 181 vs. 419 ± 76 pg/ml, P = 0.06). Net fetal glucose uptake rates were inversely proportional to fetal glucagon (r(2) = 0.38, P < 0.05), cortisol (r(2) = 0.31, P < 0.05), and NE (r(2) = 0.59, P < 0.05) concentrations. Expressions of components in the mammalian target of rapamycin signaling pathway in fetal skeletal muscle were similar between groups. In summary, prolonged infusion of amino acids directly into normally growing fetal sheep increased leucine oxidation. Amino acid-stimulated increases in fetal glucagon, cortisol, and NE may contribute to a shift in substrate oxidation by the fetus from glucose to amino acids.     

Intrauterine growth retardation in experimental diabetes: possible role of the placenta

Fetal growth disorders are common in pregnancy complicated by diabetes. Whereas macrosomia often occurs in infants of diabetic women, growth retardation is almost a rule in spontaneous and experimental diabetes in animals. However, it is not clear when during development growth inhibition starts and how placental pathology might affect fetal growth in maternal diabetes. In this study pregnant Wistar rats were injected (ip) with a single dose of 50 mg/kg of streptozotocin (STZ) on gestation day (GD) 2 and a blood glucose level of 200 mg/dl or more determined 24 hrs later indicated diabetes. The controls were non-treated, buffer treated or, following confirmation of diabetes, injected with a single dose of 2--6 IU of insulin (Novo Ultralente) once daily. Fetuses and placentae were collected from GD 14--20. Intrauterine growth retardation (IUGR) in STZ group was significant as early as GD 15 and persisted to GD 20. Insulin produced a significant recovery in fetal weight gain. The placentas of STZ-treated group were significantly heavier than those of the control groups. The reduction in cord length of the STZ group became apparent on GD 16 and remained so to term. The placenta of GD 14 STZ group had a thicker decidua basalis and dilated maternal sinusoids. By GD 16, the decidua basalis contained glycogen-containing decidual cells and scattered glycogen cells confirmed by Best's carmine with or without diastase. The glycogen cells of the basal zone were more abundant, and had degenerated in some sites leaving behind cysts with eosinophilic mass. The giant cells had proliferated enormously. The labyrinthine zone appeared spongy with persistent fetal mesenchyme, peri-vascular fibrosis, and enhanced placental barrier. The trophoblasts of the labyrinths also contained traces of glycogen unlike the controls. By GD 18, the decidua basalis of the STZ group was thinner than that of the controls and contained necrotic giant cells and lymphocytic aggregations. In the basal zone, the giant cells had proliferated further; more glycogen cells had degenerated. Perivascular fibrosis was still extensive in the labyrinthine zone. Bloodless maternal sinusoids, extensive vacuolization, degeneration of glycogen islands and formation of cysts characterized the labyrinthine zone. These changes varied in intensity from one area to another in the same placenta and between placentas of the same and of different litters. The development of the upper and lower jaws, elevation and fusion of palatal shelves, reduction of physiological umbilical hernia, descent of the testes, fusion of the urethral folds and separation of digits of the paws were significantly delayed in the STZ group. The consistent association of placental pathology with fetal growth retardation is suggestive of an alteration in placental function possibly contributing to IUGR in STZ-induced diabetes in rats.     

Fetal insulin and placental 3-O-methyl glucose clearance in near-term sheep

It is difficult, if not impossible, to measure the placental transfer of glucose directly because of placental glucose consumption and the low A-V glucose difference across the sheep placenta. We have approached the problem of quantifying placental hexose transfer by using a nonmetabolized glucose analogue (3-O-methyl glucose) which shares the glucose transport system. We have measured the clearance by using a multisample technique permitting least squares linear computing to avoid the errors implicit in the Fick principle. The placental clearance of 3-O-methyl glucose was measured in the control condition and after the administration of insulin to the fetal circulation. A glucose clamp technique was used to maintain constant transplacental glucose concentrations throughout the duration of the experiment. A control series was performed in which the only intervention was the infusion of normal saline. In these experiments the maternal and fetal glucose concentrations remained constant as did the volume of distribution of 3-O-methyl glucose in the fetus. The maternal insulin concentration remained constant and fetal insulin concentration changed from 11 +/- 2 microU/ml to 355 +/- 51 microU/ml (P less than 0.01). In the face of this large increase in fetal plasma insulin, there was no change in the placental clearance of 3-O-methyl glucose. In the control condition the clearance was 14.1 +/- 1.0 ml/min per kg and this was 13.8 +/- 1.0 ml/min per kg in the high insulin condition. Fetal insulin may change placental glucose flux by decreasing fetal plasma glucose concentrations but does not do so by changing the activity of the glucose transport system.     

Acute supplementation of amino acids increases net protein accretion in IUGR fetal sheep

Placental insufficiency decreases fetal amino acid uptake from the placenta, plasma insulin concentrations, and protein accretion, thus compromising normal fetal growth trajectory. We tested whether acute supplementation of amino acids or insulin into the fetus with intrauterine growth restriction (IUGR) would increase net fetal protein accretion rates. Late-gestation IUGR and control (CON) fetal sheep received acute, 3-h infusions of amino acids (with euinsulinemia), insulin (with euglycemia and euaminoacidemia), or saline. Fetal leucine metabolism was measured under steady-state conditions followed by a fetal muscle biopsy to quantify insulin signaling. In CON, increasing amino acid delivery rates to the fetus by 100% increased leucine oxidation rates by 100%. In IUGR, amino acid infusion completely suppressed fetal protein breakdown rates but increased leucine oxidation rate by only 25%, resulting in increased protein accretion rates by 150%. Acute insulin infusion, however, had very little effect on amino acid delivery rates, fetal leucine disposal rates, or fetal protein accretion rates in CON or IUGR fetuses despite robust signaling of the fetal skeletal muscle insulin-signaling cascade. These results indicate that, when amino acids are given directly into the fetal circulation independently of changes in insulin concentrations, IUGR fetal sheep have suppressed protein breakdown rates, thus increasing net fetal protein accretion.     

Glucose metabolic adaptations in the intrauterine growth-restricted adult female rat offspring

We studied glucose metabolic adaptations in the intrauterine growth-restricted (IUGR) rat offspring to decipher glucose homeostasis in metabolic programming. Glucose futile cycling (GFC), which is altered when there is imbalance between glucose production and utilization, was studied during a glucose tolerance test (GTT) in 2-day-old (n = 8), 2-mo-old (n = 22), and 15-mo-old (n = 22) female rat offspring. The IUGR rats exposed to either prenatal (CM/SP, n = 5 per age), postnatal (SM/CP, n = 6), or pre- and postnatal (SM/SP, n = 6) nutrient restriction were compared with age-matched controls (CM/CP, n = 5). At 2 days, IUGR pups (SP) were smaller and glucose intolerant and had increased hepatic glucose production and increased glucose disposal (P < 0.01) compared with controls (CP). At 2 mo, the GTT, glucose clearance, and GFC did not change. However, a decline in hepatic glucose-6-phosphatase (P < 0.05) and fructose-1,6-biphosphatase (P < 0.05) enzyme activities in the IUGR offspring was detected. At 15 mo, prenatal nutrient restriction (CM/SP) resulted in greater weight gain (P < 0.01) and hyperinsulinemia (P < 0.001) compared with postnatal nutrient restriction (SM/CP). A decline in GFC in the face of a normal GTT occurred in both the prenatal (CM/SP, P < 0.01) and postnatal calorie (SM/CP, P < 0.03) and growth-restricted offspring. The IUGR offspring with pre- and postnatal nutrient restriction (SM/SP) were smaller, hypoinsulinemic (P < 0.03), and hypoleptinemic (P < 0.03), with no change in GTT, hepatic glucose production, GFC, or glucose clearance. We conclude that there is pre- and postnatal programming that affects the postnatal compensatory adaptation of GFC and disposal initiated by changes in circulating insulin concentrations, thereby determining hepatic insulin sensitivity in a phenotype-specific manner.     

Effect of hypoxia on the initiation of secondary wool follicles in the fetus

The development of secondary wool follicles in single fetal sheep subjected to hypobaric hypoxaemia was studied. One group of pregnant ewes were exposed to 57.1 kPa from 30 to 135 days gestation. Fetal weights (mean +/- s.d.) for the hypoxaemic group (3.35 +/- 0.53 kg; n = 4) were significantly lower than for the controls (4.19 +/- 0.31 kg; n = 3, P less than 0.05). At 110 days gestation, a second group had arterial and venous catheters surgically implanted into the ewe and fetus and skin samples were taken from the fetus. At 120 days gestation (10 days after surgery) these animals were subjected to hypoxia for 20 days, at a level to maintain fetal carotid pO2 between 1.47 and 1.87 kPa (mean carotid pO2 for the control fetuses was 2.84 +/- 0.28 kPa). Fetal weight at 140 days was not significantly different in the hypoxaemic and control groups. Morphometric analysis revealed that the secondary to primary follicle ratio (S:P) was less in both groups of hypoxaemic fetuses than in their respective controls. Although hypoxia for 20 days did not significantly alter fetal weight, it produced a low S:P ratio similar to the longer-term hypoxaemic animals. It is concluded that hypoxia has a marked effect in reducing the initiation of secondary follicles in the last third of gestation.     

Intrauterine growth restriction decreases pulmonary alveolar and vessel growth and causes pulmonary artery endothelial cell dysfunction in vitro in fetal sheep

Intrauterine growth restriction (IUGR) increases the risk for bronchopulmonary dysplasia (BPD). Abnormal lung structure has been noted in animal models of IUGR, but whether IUGR adversely impacts fetal pulmonary vascular development and pulmonary artery endothelial cell (PAEC) function is unknown. We hypothesized that IUGR would decrease fetal pulmonary alveolarization, vascular growth, and in vitro PAEC function. Studies were performed in an established model of severe placental insufficiency and IUGR induced by exposing pregnant sheep to elevated temperatures. Alveolarization, quantified by radial alveolar counts, was decreased 20% (P < 0.005) in IUGR fetuses. Pulmonary vessel density was decreased 44% (P < 0.01) in IUGR fetuses. In vitro, insulin increased control PAEC migration, tube formation, and nitric oxide (NO) production. This response was absent in IUGR PAECs. VEGFA stimulated tube formation, and NO production also was absent. In control PAECs, insulin increased cell growth by 68% (P < 0.0001). Cell growth was reduced in IUGR PAECs by 29% at baseline (P < 0.01), and the response to insulin was attenuated (P < 0.005). Despite increased basal and insulin-stimulated Akt phosphorylation in IUGR PAECs, endothelial NO synthase (eNOS) protein expression as well as basal and insulin-stimulated eNOS phosphorylation were decreased in IUGR PAECs. Both VEGFA and VEGFR2 also were decreased in IUGR PAECs. We conclude that fetuses with IUGR are characterized by decreased alveolar and vascular growth and PAEC dysfunction in vitro. This may contribute to the increased risk for adverse respiratory outcomes and BPD in infants with IUGR.     

The kidney is resistant to chronic hypoglycaemia in late-gestation fetal sheep

We imposed a sustained reduction in glucose supply to late-gestation fetal sheep to see whether the reduction in glucose and insulin levels affected renal growth, renin expression and synthesis, and renal function. Maternal glucose concentrations were lowered to 1.7-1.9 mmol/L for 12-13 days by i.v. insulin infusion (n = 9, 121 days gestation, term = 150 days). Control ewes (n = 7) received vehicle. Maternal and fetal glucose concentrations were 40% and 31% lower than in controls (p < 0.001), respectively. Fetal plasma insulin levels fell 36% +/- 7% by day 7 (p < 0.05); IGF-I levels were unchanged. Arterial PO2 and pH increased and PCO2 fell (p < 0.05). Renal function was largely unaffected. Longitudinal growth was 28% slower and spleen weights were 36% smaller (p < 0.05); body and kidney weights were not affected. Renal renin levels and renin, angiotensinogen, and angiotensin receptor mRNA levels were similar to those of controls. Plasma renin levels increased from 2.1 +/- 0.6 to 7.6 +/- 2.8 ng angiotensin I.mL-1.h-1 (p = 0.01). Thus reductions in fetal glucose and insulin levels in late gestation that were sufficient to retard skeletal growth had no effect on kidney growth or function or the renal renin-angiotensin system, possibly because IGF-I levels were not reduced. There was, however, increased activity of the circulating renin-angiotensin system similar to that seen during insulin-induced hypoglycaemia.     

Effect of maternal exercise on fetal liver glycogen late in gestation in the rat

To determine the effect of maternal exercise on fetal liver glycogen content, fed and fasted rats that were pregnant for 20.5 or 21.5 days were run on a rodent treadmill for 60 min at 12 m/min with a 0% grade or 16 m/min up a 10% grade. The rats were anesthetized by intravenous injection of pentobarbital sodium, and fetal and maternal liver and plasma samples were collected and frozen. Fetal liver glycogenolysis did not occur as a result of maternal exercise. Fetal blood levels of lactate increased 22-60%, but glucose, plasma glucagon, and insulin were unchanged during maternal exercise. Maternal liver glycogen decreased as a result of exercise in all groups of rats except the fasted 20.5-day-pregnant group. Plasma free fatty acids increased in all groups and blood lactate increased in fed (20.5 days) and fasted (21.5 days) pregnant rats. Maternal glucose, glucagon, and insulin values remained constant during exercise. The fetus appears to be well-protected from metabolic stress during moderate-intensity maternal exercise.     

Developmental changes in ovine myocardial glucose transporters and insulin signaling following hyperthermia-induced intrauterine fetal growth restriction

Developmental changes in ovine myocardial glucose transporters and insulin signaling following hyperthermia-induced intrauterine fetal growth restriction (IUGR) were the focus of our study. Our objective was to test the hypothesis that the fetal ovine myocardium adapts during an IUGR gestation by increasing glucose transporter protein expression, plasma membrane-bound glucose transporter protein concentrations, and insulin signal transduction protein concentrations. Growth measurements and whole heart tissue were obtained at 55 days gestational age (dGA), 90 dGA, and 135 dGA (term = 145 dGA) in fetuses from control (C) and hyperthermic (HT) pregnant sheep. Additionally, in 135 dGA animals, arterial blood was obtained and Doppler ultrasound was used to determine umbilical artery systolic (S) and diastolic (D) flow velocity waveform profiles to calculate pulsatility (S - D/mean) and resistance (S - D/S) indices. Myocardial Glut-1, Glut-4, insulin signal transduction proteins involved in Glut-4 translocation, and glycogen content were measured. Compared to age-matched controls, HT 90-dGA fetal body weights and HT 135-dGA fetal weights and gross heart weights were lower. Heart weights as a percent of body weights were similar between C and HT sheep at 135 dGA. HT 135-dGA animals had (i) lower fetal arterial plasma glucose and insulin concentrations, (ii) lower arterial blood oxygen content and higher plasma lactate concentrations, (iii) higher myocardial Glut-4 plasma membrane (PM) protein and insulin receptor beta protein (IRbeta ) concentrations, (iv) higher myocardial glycogen content, and (v) higher umbilical artery Doppler pulsatility and resistance indices. The HT ovine fetal myocardium adapts to reduced circulating glucose and insulin concentrations by increasing plasma membrane Glut-4 and IRbeta protein concentrations. The increased myocardial Glut-4 PM and IRbeta protein concentrations likely contribute to or increase the intracellular delivery of glucose and, together with the increased lactate concentrations, enhance glycogen synthesis, which allows for maintained myocardial growth commensurate with fetal body growth.     

Effect of hyperinsulinemia on amino acid utilization and oxidation independent of glucose metabolism in the ovine fetus

We studied the effect of acute hyperinsulinemia on amino acid (AA) utilization and oxidation rates independent of insulin-enhanced glucose metabolism in fetal sheep. Metabolic studies were conducted in each fetus (n = 11) under three experimental periods. After control period (C) study, a fetal hyperinsulinemic-euglycemic-euaminoacidemic (HI-euG-euAA) clamp was established, followed by a hyperinsulinemic-hypoglycemic-euaminoacidemic (HI-hypoG-euAA) clamp to decrease glucose metabolic rates toward C values. Infusions of (3)H(2)0, L-[1-(13)C]leucine, and [(14)C(U)]glucose were administered to measure blood flow, leucine oxidation, and fetal glucose uptake, utilization, and oxidation in each period. Fetal glucose utilization rate increased 1.7-fold with hyperinsulinemia (C 5.8 +/- 0.8 mg.kg(-1).min(-1), HI-euG-euAA 10 +/- 1.3 mg.kg(-1).min(-1), P < 0.0001), returning to rates not different from C with hypoglycemia (HI-hypoG-euAA 7.1 +/- 0.9 mg.kg(-1).min(-1) vs. C value, P = 0.15). Fetal glucose oxidation rate increased 1.7-fold with hyperinsulinemia (C 3.1 +/- 0.2 mg.kg(-1).min(-1), HI-euG-euAA 5.4 +/- 0.4 mg.kg(-1).min(-1), P < 0.0001) and decreased to near control rates with hypoglycemia (4.0 +/- 0.3 HI-hypoG-euAA vs. C value, P = 0.006). AA utilization rates increased with hyperinsulinemia for all essential and most nonessential AAs (P < 0.001) and did not change when insulin-induced increases in glucose utilization returned to control rates. Leucine oxidation rate increased 1.7-fold with hyperinsulinemia (C 1.0 +/- 0.3 micromol.min(-1).kg(-1), HI-euG-euAA 1.7 +/- 0.3 micromol.min(-1).kg(-1), P < 0.002) and did not change when glucose oxidation rate was decreased with hypoglycemia. These results demonstrate that, in fetal sheep, insulin promotes AA utilization and oxidation independent of its simultaneous effects on glucose metabolism. In acute hyperinsulinemic conditions, AA oxidation does not change when insulin-induced glucose utilization is prevented.     

Ease of calving, blood chemistry, insulin and bovine growth hormone of newborn calves derived from embryos produced in vitro in culture systems with serum and co-culture or with PVA

Blood chemistry (pH, pCO2, pO2, glucose, lactate) as well as plasma insulin and growth hormone of calves derived from embryos produced under 2 different in vitro culture systems (modified SOFaa with 20% serum and co-culture with bovine oviduct epithelial cells [IVP serum, n=8] or with 3 mg/mL PVA [IVPdefined, n=6]) were compared with those of calves derived from AI (n=5). Calvings were classified according to the ease (unassisted, light traction, heavy traction). Blood samples were taken from the jugular vein of calves at 5, 15, 30 and 60 min, and at 2, 3, 6, 12, 18 and 24 h after delivery, then daily for 6 d. At the second day of life after 4 feedings and a 4-h fasting period, a glucose tolerance test was performed to evaluate glucose metabolism and insulin secretion. Calves in the IVP serum group had higher birth weights than AI calves (LS mean +/- SEM, IVP serum: 45.2 +/- 1.4 kg vs AI: 40.4 +/- 1.7 kg; P < 0.05), while the birth weights of calves in the IVP defined group were in between (IVPdefined: 41.9 +/- 1.6 kg). More IVP serum calves (75%) needed assistance than IVP defined (33%) or AI (40%) calves. The effect of ease of calving vs the effect of embryo culture was compared in relation to blood parameters at birth. There was an effect of ease of calving but not of embryo culture conditions on blood pH, lactate and PCO2. Calves requiring heavy traction had lower pH during the first 3 h after calving, a higher lactate during the first 60 min after calving and a higher pCO2 the first 2 h after calving than calves born unassisted. Calves requiring heavy traction also had lower pH the first 2 h and higher lactate the first 3 h after calving than calves born by light traction. IVP defined calves had lower lactate than IVP serum calves the first 60 min after calving. At 6 h after delivery, all blood parameters had stabilized. There was no effect of either embryo culture or ease of calving on basal insulin and growth hormone level, or the ability of the calves to handle glucose postnatally and during a glucose tolerance test.     

Effects of Maternal LPS Exposure during Pregnancy on Metabolic Phenotypes in Female Offspring

It is increasingly recognized that intra-uterine growth restriction (IUGR) is associated with an increased risk of metabolic disorders in late life. Previous studies showed that mice exposed to LPS in late gestation induced fetal IUGR. The present study investigated the effects of maternal LPS exposure during pregnancy on metabolic phenotypes in female adult offspring. Pregnant mice were intraperitoneally injected with LPS (50 µg/kg) daily from gestational day (GD)15 to GD17. After lactation, female pups were fed with standard-chow diets (SD) or high-fat diets (HFD). Glucose tolerance test (GTT) and insulin tolerance test (ITT) were assessed 8 and 12 weeks after diet intervention. Hepatic triglyceride content was examined 12 weeks after diet intervention. As expected, maternal LPS exposure during pregnancy resulted in fetal IUGR. Although there was an increasing trend on fat mass in female offspring whose dams were exposed to LPS during pregnancy, maternal LPS exposure during pregnancy did not elevate the levels of fasting blood glucose and serum insulin and hepatic triglyceride content in female adult offspring. Moreover, maternal LPS exposure during pregnancy did not alter insulin sensitivity in adipose tissue and liver in female adult offspring. Further analysis showed that maternal LPS exposure during pregnancy did not exacerbate HFD-induced glucose tolerance and insulin resistance in female adult offspring. In addition, maternal LPS exposure during pregnancy did not aggravate HFD-induced elevation of hepatic triglyceride content in female adult offspring. In conclusion, LPS-induced IUGR does not alter metabolic phenotypes in adulthood.     

Insulin-induced translocation of facilitative glucose transporters in fetal/neonatal rat skeletal muscle

We examined the effect of insulin on fetal/neonatal rat skeletal muscle GLUT-1 and GLUT-4 concentrations and subcellular distribution by employing immunohistochemical analysis and subcellular fractionation followed by Western blot analysis. We observed that insulin did not alter total GLUT-1 or GLUT-4 concentrations or the GLUT-1 subcellular distribution in fetal/neonatal or adult skeletal muscle in 60 min. The basal and insulin-induced changes in subcellular distribution of GLUT-4 were different between the fetal/neonatal and adult skeletal muscle. Under basal conditions, sarcolemma-associated GLUT-4 was higher in the newborn compared with the adult, translating into a higher glucose transport. In contrast, insulin-induced translocation of GLUT-4 to the sarcolemma- and insulin-induced glucose transport was lower in the newborn compared with the adult. This age-related change results in enhanced basal glucose transport to fuel myocytic proliferation and differentiation while relatively curbing the insulin-dependent glucose transport in the newborn.     

S(G), S(I), and EGP of exercise-trained middle-aged men estimated by a two-compartment labeled minimal model

To examine the effects of physical training on glucose effectiveness (S(G)), insulin sensitivity (S(I)), and endogenous glucose production (EGP) in middle-aged men, stable-labeled frequently sampled intravenous glucose tolerance tests (FSIGTT) were performed on 11 exercise-trained middle-aged men and 12 age-matched sedentary men. The time course of EGP during the FSIGTT was estimated by nonparametric stochastic deconvolution. Glucose uptake-specific indexes of glucose effectiveness (S(2*)(G) x 10(2): 0.81 +/- 0.08 vs. 0.60 +/- 0.05 dl. min(-1). kg(-1), P < 0.05) and insulin sensitivity [S(2*)(I) x 10(4): 24.59 +/- 2.98 vs. 11.89 +/- 2.36 dl. min(-1). (microU/ml)(-1). kg(-1), P < 0.01], which were analyzed using the two-compartment minimal model, were significantly greater in the trained group than in the sedentary group. Plasma clearance rate (PCR) of glucose was consistently greater in the trained men than in sedentary men throughout FSIGTT. Compared with sedentary controls, EGP of trained middle-aged men was higher before glucose load. The EGP of the two groups was similarly suppressed by approximately 70% within 10 min, followed by an additional suppression after insulin infusion. EGP returned to basal level at approximately 60 min in the trained men and at 100 min in the controls, followed by its overshoot, which was significantly greater in the trained men than in the controls. In addition, basal EGP was positively correlated with S(2*)(G) . The higher basal EGP and greater EGP overshoot in trained middle-aged men appear to compensate for the increased insulin-independent (S(2*)(G)) and -dependent (S(2*)(I)) glucose uptake to maintain glucose homeostasis.