Effect of increased substrate availability on fatty acid synthesis in the growth retarded fetus

The purpose of this study was to test the hypothesis that increased substrate (glucose) availability will enhance fatty acid synthesis in the growth retarded rat fetus. At 17 days of gestation, 19 time-dated pregnant rats had one uterine artery ligated, leading to growth retardation (IUGR) in the fetuses located on the uterine horn supplied by the ligated artery. The uterine artery of the opposite uterine horn was left untouched, resulting in appropriately grown fetuses, which served as controls. At 21 days of gestation the animals were infused with either 20% dextrose or 0.9% saline via a maternal jugular vein catheter for 4 hr. Fetal organ fatty acid synthesis was measured by maternal ³H₂O injection. In the growth retarded saline infused fetus, specific activity for ³H (representing rate of fatty acid synthesis) was significantly lower in fetal liver, lung and carcass. Dextrose infusion resulted in increased fatty acid synthesis in both control and IUGR fetuses in all tissues cited above. The specific activity in glucose infused IUGR fetal organs equalled that of saline infused control fetuses. The data indicate that maternal glucose infusion resulted in an increased rate of fatty acid synthesis, in IUGR fetuses; consequently, the deficit in fatty acid synthesis in the IUGR fetus (compared to appropriately grown control fetuses) was abolished.     

Circulating metabolite utilization by periuterine adipose tissue in situ in the pregnant rat

To study the use of glucose for lipid synthesis by the periuterine adipose tissue in situ, 14C-glucose was infused through the left uterine artery of anesthetized, fed pregnant and virgin control rats. A greater amount of 14C-lipid always appeared in the adipose tissue from the left uterine horn than in the tissue from the right uterine horn, indicating direct utilization of the infused 14C-glucose by the tissue. Glucose utilization for both glycerol and fatty acid synthesis increased from day 0 (virgin rats) to day 20 of gestation and then decreased dramatically on day 21. In virgin and 12-day pregnant rats, glucose was incorporated into either lipidic moiety at similar rates, whereas in late pregnant rats glucose utilization for glyceride glycerol synthesis was four to five times greater than for fatty acids. The utilization of circulating fatty acids and the lipoprotein triglyceride-derived fatty acids was studied by infusing 14C-palmitate or 14C-triolein-labeled very-low-density lipoprotein (VLDL) through the left uterine artery in both virgin and 20-day pregnant rats. Incorporation of fatty acids from either one of these plasma sources was significantly higher in the pregnant than in virgin rats. This high amount of fatty acid acquisition did not account for the very active glyceride glycerol synthesis observed in pregnant rats and can only be explained by the intracellular reesterification of some lipolytic fatty acids. The results suggest a highly accelerated triacylglycerol/fatty acid substrate cycle in adipose tissue during late pregnancy, which would allow active esterification (contributing to fat accumulation) and responsive lipolysis (permitting rapid fat mobilization) by the mother.     

Maternal-fetal fat transport versus new fat synthesis in the pregnant diabetic rat

Summary Rats were made diabetic by the injection of streptozotocin on day 12 of pregnancy and were investigated on days 17 and 20 of pregnancy. A significant correlation between both maternal plasma triglyceride and nonesterified fatty acid levels with placental or fetal triglyceride content was found, although fetal weight did not change significantly. In order to investigate the source of the placental and fetal fat the rats received, intragastrically 24 h earlier, 1-¹⁴C-triolein (as a preformed fatty acid tracer) and tritiated water (as a marker of de novo fatty acid synthesis). Several maternal tissues, placenta, and fetuses were extracted and analysed for fatty acid radioactivity. Compared with non-diabetic pregnant rats, maternal ¹⁴C-label storage was reduced. In contrast, the placental and fetal tissues demonstrated a significant rise in ¹⁴C-label, similar in magnitude to the rise in their triglyceride content. The pattern of ³H incorporation also indicated a pronounced decrease in maternal fatty acid synthesis, but no increase in de novo fatty acid synthesis in the fetus or placenta. The findings show that fetal lipids in the pregnant rat originate both from maternal fatty acids and those synthesized in situ. The diabetes-induced increment in fetal triglyceride content is derived, however, from preformed maternal triglycerides or non-esterified fatty acids secondary to the increase in their concentration in the maternal circulation.     

Role of the availability of substrates on hepatic and renal gluconeogenesis in the fasted late pregnant rat

Studies were conducted to examine the role of gluconeogenetic substrate availability on glucose production in the fasted late pregnant rat. Virgin and 21-day pregnant rats were studied after 24 hours' food deprivation. Pregnant animals showed decreased circulating glucose and gluconeogenic amino acid and increased plasma glycerol concentration. Glucose formation was studied in vivo two, five, and ten minutes after the intravenous administration of two concentrations of 14C-alanine, 14C-pyruvate, or 14C-glycerol. Concentrations of 0.2 mmols of 14C-glycerol or 14C-pyruvate, but not of 14C-alanine, enhanced 14C-glucose production in pregnant rats, whereas 1 mmol of any of the three 14C-substrates always enhanced 14C-glucose production in these rats. Both 1 mmol/L and 5 mmol/L 14C-alanine increased 14C-glucose formation in 90-minute-incubated liver slices of fasted pregnant rats, in spite of decreased cytosolic activity of alanine aminotransferase. The three substrates enhanced "in vitro" renal gluconeogenesis in pregnant rats. Under all experimental conditions studied, labeled glycerol was converted more efficiently into glucose than equivalent amounts of any other substrate used, and this difference was greater in pregnant, than in virgin animals. Results indicate that, in spite of enhanced gluconeogenetic activity, maternal glucose production in the fasted state at late gestation is limited by the deficiency of certain substrates, such as amino acids. It is proposed that glycerol derived from enhanced maternal adipose tissue lipolysis constitutes a preferential gluconeogenetic substrate in comparison with others, such as alanine, that are more efficiently transferred through the placenta to the fetus.     

Effect of insulin on glucose uptake by the maternal hindlimb and uterus, and by the fetus in conscious pregnant sheep

Previous studies have demonstrated the presence of insulin receptors on the maternal surface of the placenta in several species and the specific binding of insulin to the placenta in sheep. However, both in-vitro and in-vivo studies have produced conflicting evidence concerning the effect of insulin on placental glucose uptake. To clarify this problem, we measured maternal hindlimb, uterine and fetal glucose and oxygen extractions and glucose/oxygen quotients in chronically catheterized, non-stressed, late-gestation pregnant sheep over 1 h at a constant concentration of arterial plasma glucose, and again during the next 2 h at the same glucose level but at a higher insulin concentration using glucose 'clamp' methodology. Insulin produced a 4.9-fold increase in glucose extraction and a 3.5-fold increase in glucose/oxygen quotient across the hindlimb; in contrast, insulin did not significantly affect uterine or fetal glucose extraction or glucose/oxygen quotient. We conclude that in contrast to other tissues of the pregnant ewe, placental glucose uptake and transfer are insensitive to variations in maternal insulin concentration.     

Enzymatic determination of 1-14C-glucose in pig plasma

Summary A simple and cheap one-step enzymatic method has been developed for the determination of 1-¹⁴C-glucose in plasma. C-1 of glucose is cleaved off as CO₂ by treatment with hexokinase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconic dehydrogenase. True 1-¹⁴C-glucose activity is then calculated as the difference between total radioactivity and radioactivity remaining after enzyme treatment and evaporation. The reaction is shown to be quantitative and specific, thus eliminating both labelled metabolites and label recycled to other positions in glucose. Two different types of pig experiments show that 1-¹⁴C-glucose, when determined by this method, is as irreversible a tracer as the commonly used 3-³H-glucose.     

Glyburide crosses the placenta in vivo in pregnant rats

Summary Non-insulin-dependent diabetes mellitus (NIDDM) is normally treated by oral hypoglycaemic agents, but their use is excluded during pregnancy because of their potential teratogenic and hypoglycaemic effects on the fetus. This caveat was recently questioned as glyburide was shown to cross an isolated cotyledon in vitro in insignificant amounts. In the present study, placental transport of glyburide in vivo was examined as an indispensable step towards clinical trials. Tritiated glyburide, C¹⁴ albumin or C¹⁴-labelled diazepam were injected into 13, 9 and 11 pregnant rats, respectively and the radioactivity was measured thereafter in maternal blood and in whole fetal extracts. The ratios between radioactivity in fetal tissue to that in maternal blood for glyburide (0.535 ± 0.068) were similar to those of diazepam (0.641 ± 0.057) which readily crosses the placenta. However, they differed significantly from those for albumin (0.048 ± 0.0004) which does not cross. Moreover, glyburide in fetal tissue consistently reflected its concentration in maternal blood when measured at consecutive intervals after intravenous injection in the mother. In contrast, albumin in fetal tissue was low at all time points regardless of its levels in maternal blood when measured at different times after injection. These data suggest that glyburide crosses the placenta of pregnant rats and should therefore be considered with caution as a hypoglycaemic agent in the treatment of gestational diabetes. [Diabetologia (1995) 38: 753–756] Received: 9 June 1994 and in revised form: 6 December 1994     

Effects of dexamethasone on the glucogenic capacity of fetal, pregnant, and non-pregnant adult sheep

Fetal glucocorticoids have an important role in the pre-partum maturation of physiological systems essential for neonatal survival such as glucogenesis. Consequently, in clinical practice, synthetic glucocorticoids, like dexamethasone, are given routinely to pregnant women threatened with pre-term delivery to improve the viability of their infants. However, little is known about the effects of maternal dexamethasone treatment on the glucogenic capacity of either the fetus or mother. This study investigated the effects of dexamethasone treatment using a clinically relevant dose and regime on glycogen deposition and the activities of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) in the liver and kidney of pregnant ewes and their fetuses, and of non-pregnant ewes. Dexamethasone administration increased the glycogen content of both the fetal and adult liver within 36 h of beginning treatment. It also increased G6Pase activity in the liver and kidney of the fetuses but not of their mothers or the non-pregnant ewes. Neither hepatic nor renal PEPCK activity was affected by dexamethasone in any group of animals. These changes in glycogen content and G6Pase activity were accompanied by rises in the plasma glucose and insulin concentrations and by a fall in the plasma cortisol level in the fetus and both groups of adult animals. In addition, dexamethasone treatment raised fetal plasma tri-iodothyronine (T(3)) concentrations and reduced maternal levels of plasma T(3) and thyroxine, but had no effect on thyroid hormone concentrations in the non-pregnant ewes. These findings show that maternal dexamethasone treatment increases the glucogenic capacity of both the mother and fetus and has major implications for glucose availability both before and after birth.     

Effects of insulin at two dose levels on gluconeogenesis from alanine in fasting man

We have determined the effect of insulin infused at 1 and 5 mU/kg/min on gluconeogenesis from alanine in 48-hr fasted men. The conversion of alanine to glucose was measured by the arterial-hepatic venous catheterization technique combined with the infusion of ¹⁴C-alanine. During insulin infusion, euglycemia was maintained by variable glucose infusion. When insulin was infused at 1 mU/kg/min the net splanchnic production of ¹⁴C-glucose was suppressed by 80% but glucagon infused at the end of the study resulted in substantial release of ¹⁴C-glucose from the liver suggesting marked accumulation of labeled glucose in glycogen. When insulin was infused at 5 mU/kg/min the splanchnic release of ¹⁴C-glucose was also markedly suppressed but in contrast to the lower insulin dose very little labeled glucose accumulated in glycogen. Neither the high nor the low dose insulin infusion had any effect on net splanchnic alanine uptake and plasma glucagon levels fell by 35% in both protocols. These data demonstrate that in 48-hr fasted man, (1) a small increment in insulin concentration will suppress glucose production but mostly by diverting the newly formed glucose into glycogen; (2) at higher concentrations, insulin will inhibit glucose production mainly by suppressing gluconeogenesis; and (3) this insulin-induced suppression of gluconeogenesis is due to an intrahepatic effect rather than an effect on the splanchnic extraction of alanine.     

Adipose tissue-derived FABP4 mediates glucagon-stimulated hepatic glucose production in gestational diabetes

Aims

One of the most common complications of pregnancy is gestational diabetes mellitus (GDM), which may result in significant health threats of the mother, fetus and the newborn. Fatty acid-binding protein 4 (FABP4) is an adipokine that regulates glucose homeostasis by promoting glucose production and liver insulin resistance in mouse models. FABP4 levels are increased in GDM and correlates with maternal indices of insulin resistance, with a rapid decline post-partum. We therefore aimed to determine the tissue origin of elevated circulating FABP4 levels in GDM and to assess its potential contribution in promoting glucagon-induced hepatic glucose production.

Materials and Methods

FABP4 protein and gene expression was determined in biopsies from placenta, subcutaneous (sWAT) and visceral (vWAT) white adipose tissues from GDM and normoglycaemic pregnant women. FABP4 differential contribution in glucagon-stimulated hepatic glucose production was tested in conditioned media before and after its immune clearance.

Results

We showed that FABP4 is expressed in placenta, sWAT and vWAT of pregnant women at term, with a significant increase in its secretion from vWAT of women with GDM compared with normoglycaemic pregnant women. Neutralizing FABP4 from both normoglycaemic pregnant women and GDM vWAT secretome, resulted in a decrease in glucagon-stimulated hepatic glucose production.

Conclusions

This study provides new insights into the role of adipose tissue-derived FABP4 in GDM, highlighting this adipokine, as a potential co-activator of glucagon-stimulated hepatic glucose production during pregnancy.     

The in vivo metabolism of 14C-glucose and 14C-glycine in insulin-treated northern pike (Esox lucius L.)

The effects of codfish insulin (2 IU/kg) on ¹⁴C-glucose and ¹⁴C-glycine metabolism in vivo were studied in cannulated Northern pike (Esox lucius L.). Insulin significantly reduced plasma glucose levels and increased the incorporation of ¹⁴C-glucose carbon into liver and muscle lipid and muscle protein, and of ¹⁴C-glycine carbon into muscle protein. These results suggest that the metabolic role of insulin in pike is similar to that observed in mammals.     

Insulin sensitivity of adipose tissue in vitro and the response to exogenous insulin in obese human subjects

The effect of varying concentrations of insulin on 1-¹⁴C-glucose conversion to ¹⁴CO₂ was measured in subcutaneous adipose tissue samples obtained from 16 obese human subjects (10 nondiabetic, 6 diabetic). An index of insulin sensitivity in vitro, K_ins, was calculated as the concentration of insulin stimulating one-half maximal ¹⁴CO₂ production. An index of insulin sensitivity in vivo, K_itt, was calculated as the rate constant for decrease in blood glucose after rapid intravenous administration of 0.05 U/kg insulin. There was, over-all, a significant correlation between K_ins and K_itt, indicating that insulin sensitivity of 1-¹⁴C-glucose oxidation by adipose tissue in vitro reflects the general state of sensitivity of glucose metabolism to insulin in vivo in obese human subjects. The mean values for both K_ins and K_itt in the nondiabetic subjects were significantly different from those in the diabetic subjects, indicating greater sensitivity to insulin in the former group. The nondiabetic group was also distinguished by a significantly greater plasma insulin: blood glucose ratio in the oral glucose tolerance test. These results support the view that tissue insulin sensitivity as well as pancreatic beta cell response play an important role in determining glucose tolerance in obesity.     

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

Summary 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 μmol · 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. [Diabetologia (1996) 39: 785–792] Received: 2 October 1995 and in final revised form: 1 February 1996     

Development of phosphatidyl glycerol biosynthesis in the lungs of fetuses of diabetic rats

Summary The lungs of fetuses of streptozotocin-diabetic rats were examined for their ability to incorporate U-¹⁴C-glucose into phosphatidyl choline, phosphatidyl glycerol, phosphatidyl inositol and lysophosphatidyl choline. In the lungs of control rats an increased biosynthesis of phosphatidyl glycerol in late pregnancy suggested a close association between the production of this phospholipid and the terminal maturation of the fetal lung. In the offspring of diabetic rats the incorporation of ¹⁴C-glucose into phosphatidyl choline, lysophosphatidyl choline and phosphatidyl glycerol was markedly decreased compared with the control rats on gestational day 20, whereas no difference was seen at day 22. Insulin treatment of the pregnant rats restored the biosynthesis of phosphatidyl choline and lysophosphatidyl choline towards normal on gestational day 20, while the ratio of phosphatidyl glycerol to phosphatidyl inositol incorporation of ¹⁴C-glucose was decreased, suggesting that the biosynthesis of phosphatidyl glycerol is more sensitive than that of phosphatidyl choline and lysophosphatidyl choline to the metabolic disturbances inherent in maternal diabetes. The delayed fetal pulmonary maturation occurred without fetal hyperinsulinism which suggests that this latter feature may not be of crucial significance in the aetiology of the respiratory distress syndrome.     

Placental transfer and uptake of 2-deoxyglucose in control and diabetic rats.

Placental glucose transfer and sequestration were investigated in anesthetized control and streptozotocin-diabetic rats by perfusing the fetal side of one placenta in situ while infusing a mixture of [3H]D-glucose (to measure net transfer after metabolism) and [14C]2-deoxyglucose (to estimate tissue sequestration) into the maternal circulation. No difference was found between transfer ratios (perfusate/simultaneous maternal plasma ratio) of [3H]D-glucose (0.35 +/- 0.06, mean +/- SD) and [14C]2-deoxyglucose (0.36 +/- 0.06) in control rats. Ratios were reduced (P < .001) to the same extent in diabetic rats ([3H]D-glucose, 0.13 +/- 0.06; [14C]2-deoxyglucose, 0.15 +/- 0.07). Placental glucose utilization, estimated by the quantity of [14C]2-deoxyglucose-6-phosphate present, was increased from 66 nmol.min-1.g-1 in control to 595 nmol.min-1.g-1 (P < .001) in diabetic rats. Transfer to the perfusion fluid of unlabeled D-glucose was increased (P < .001) in diabetic rats (2.32 mumol/mL) compared with control rats (0.77 mumol/mL) due to elevated (P < .001) maternal plasma glucose levels. Upon phosphorylation, 2-deoxyglucose becomes trapped within the placenta, and therefore these results indicate that all the glucose destined for direct transfer to the fetus is protected from phosphorylation while traversing the placenta, and that diabetes appears to increase placental glucose utilization, but does not induce futile cycling of glucose in an attempt to protect the fetus from an excessive influx of glucose from the mother in the rat.     

The placental lactogen receptor in maternal and fetal sheep liver: regulation by glucose and role in the pathogenesis of fasting during pregnancy.

To clarify the roles of glucose and insulin in the regulation of the PL receptor in fetal and maternal sheep liver, we administered iv glucose to pregnant ewes during a 72-h fast. The binding of ovine PL (oPL) to hepatic membranes from glucose-infused ewes and their fetuses was compared with the binding of oPL to tissues of fasted, saline-infused sheep and sheep fed normally ad libitum. Fasting of pregnant ewes caused a 58-70% reduction in the number of PL receptors in fetal and maternal liver. Intravenous administration of glucose during fasting increased the number of PL receptors in fetal liver by 137.4%. In contrast, glucose administration during fasting had no effect on the number of PL receptors in maternal liver. The number of PL binding sites in fetal liver correlated positively with fetal weight (r = 0.59) and length (r = 0.54) and with fetal plasma glucose (r = 0.69) and insulin (r = 0.55) concentrations. In contrast, PL binding was inversely related to fetal plasma oPL concentrations (r = -0.70). These findings suggested that glucose, insulin, and/or oPL may regulate PL binding in the ovine fetus. To determine whether glucose or insulin exert direct effects on the PL receptor in ovine fetal tissues, we examined the binding of radiolabeled oPL to ovine fetal hepatocytes and fibroblasts in culture. The specific binding of oPL to fetal hepatocytes was low and variable (1.0 +/- 0.5%) and it was not possible to assess reliably the effects of glucose or insulin supplementation. The specific binding of oPL to fetal fibroblasts (5.4 +/- 0.6%/mg) was unaffected by variations in media glucose concentrations (5.5-16.5 mM) or by pretreatment with insulin (10-1000 ng/ml). The results of these studies demonstrate that glucose and other nutritional factors regulate the expression of the PL receptor in fetal and maternal sheep liver. Alterations in PL binding play roles in the metabolic adaptation of the mother and fetus to nutritional deprivation and stress.     

Fetal plasma insulin and thyroid hormone levels during acute in utero ethanol exposure in a maternal-fetal sheep model

The effects of acute in utero ethanol (ETOH) treatment on basal and stimulated thyroid and insulin levels in fetal plasma were studied in chronically cannulated fetal sheep. In test situations, pregnant ewes (0.78-0.88 gestation) which were chronically cannulated received 2 g/kg ETOH [25% (vol/vol) in isotonic saline] for 2 h; this was followed by a maintenance iv infusion of 0.13 g/kg ETOH. Control animals received isovolemic infusions of isotonic saline. Fetal arterial plasma samples were obtained after the 2-h infusion, and basal levels of T3, T4, glucose, and insulin were measured. The 2-h ETOH infusion did not influence fetal basal plasma T3, T4, insulin, or glucose. Fetal thyroid responses to an intraarterial injection of 0.01, 0.10, 1.00, or 10.00 micrograms/kg TRH or of 5 mU/kg TSH through the fetal catheters were studied in the presence or absence of high plasma ETOH concentrations. Fetal T4 or T3 levels during the 4 h following any of these stimuli were not significantly different in ethanol-treated and control animals. The effects of acute ETOH exposure on insulin responses to a glucose challenge were studied in six chronically cannulated ewes and their fetuses using a cross-over experimental design. After the 2-h ETOH infusion, ewes received a bolus injection of 600 mg/kg 50% glucose, followed by a 1-h infusion of 624 mg/kg 50% glucose and 0.13 g/kg ETOH. In control situations, ewes received saline plus glucose. Acute ETOH treatment did not influence maternal or fetal plasma glucose levels at any time, but enhanced both maternal and fetal insulin responses to glucose. Total insulin release, as measured by the area under the insulin response curve, was greater during ETOH exposure in both mother (ETOH, 4740 +/- 1475 microU/ml X min; control, 2807 +/- 766 microU/ml X min; P = 0.05) and fetus (ETOH, 562 +/- 94 microU/ml X min; control, 363 +/- 46 microU/ml X min; P less than 0.05). Thus acute in utero ETOH exposure does not diminish plasma levels of either thyroid hormones or insulin, two important hormones for fetal growth and development. However, ethanol exposure enhances the insulin response to increases in blood glucose in both mother and fetus.     

Placental transport of low molecular weight heparin in the pregnant sheep

Standard heparin, an effective treatment for antepartum thromboembolic disease, is thought to be safe for the fetus since it does not cross the placenta. Recently, a number of low molecular weight heparins have been prepared which have been shown to produce less bleeding than standard heparin for an equivalent antithrombotic effect in experimental animals. These observations suggest that the low molecular weight heparins may also provide superior antithrombotic therapy in antepartum thromboembolic disease. However, it is not known whether the low molecular weight heparins cross the placenta. To determine this, we examined the pharmacokinetics of 125I-labelled standard heparin and a low molecular weight heparin, and their anticoagulant effects in mother and fetus, using a pregnant sheep model. Catheters were inserted into maternal and fetal femoral arteries at 108-119 d gestation (term: 147 d). 1-3 days later the mothers were given a bolus i.v. injection of 5000 anti-Xa units of 125I-labelled standard heparin or low molecular weight heparin, CY 222. Nine serial blood samples were collected over 4 h from both mother and fetus for measurements of radioactivity, anti-Xa activity (chromogenic) and activated partial thromboplastin times. When therapeutic levels of standard and CY 222 heparins were achieved in the mother, there was no detectable radioactivity or anticoagulant effect in the fetus. We conclude that standard heparin and the low molecular weight CY 222 do not cross the placenta in the pregnant sheep.     

Ghrelin gene expression is markedly higher in fetal pancreas compared with fetal stomach: effect of maternal fasting

Ghrelin is an orexigenic peptide secreted mainly by the stomach in adult rats. Ghrelin concentrations increase with fasting and decrease after food intake. Ghrelin is also present in the placenta and in the fetal stomach, but the role of fetal ghrelin remains unclear. In this study, we compared changes in plasma ghrelin, insulin, and glucose concentrations and in ghrelin gene expression in stomach, pancreas, and placenta in response to fasting and feeding in adult nonpregnant rats and in 20-d pregnant dams and their fetuses. Plasma total ghrelin concentrations were three times higher in the fetus than in the dam but did not increase in response to fasting. In contrast to total ghrelin, plasma active ghrelin concentrations wee 50% lower in the fetus compared with the adult pregnant rat. Ghrelin mRNA and total ghrelin were markedly elevated in the fetal pancreas and six to seven times greater than in the fetal stomach but were not affected by fasting. In contrast, fetal pancreas and stomach active ghrelin concentrations increased two to three times after maternal fasting. Ghrelin receptor mRNA was present in all fetal pancreas samples. Placenta ghrelin gene expression was detectable but low. These data raise the possibility that in the fetus, in contrast to the adult, the pancreas and not the stomach is a major source of circulating immunoreactive ghrelin. Furthermore, the presence of a strong ghrelin gene expression and of ghrelin receptor mRNA in the fetal pancreas is intriguing and suggests that ghrelin may play an important role in beta-cell development.     

Studies of insulin sensitivity in vivo in weanling rats with hypothalamic obesity

Studies were performed in weanling male rats with bilateral lesions in the ventromedial hypothalamic nuclei (VMN) and sham-operated controls to evaluate (1) the endogenous insulin response to glucose, and (2) the sensitivity to exogenous insulin as manifested by both hypoglycemia and the utilization of simultaneously injected ¹⁴C-glucose. VMN rats exhibited basal hyperinsulinemia and an increased insulin secretory response to glucose. VMN and control rats exhibited similar hypoglycemic responses to exogenous insulin. Utilization of intraperitoneally injected ¹⁴C-glucose by epididymal adipose tissue and diaphragm was similarly increased by insulin in the two groups of animals. The results exclude peripheral insulin resistance as the basis for hyperinsulinemia and support the belief that it is a direct consequence of the hypothalamic lesion.