Effects of insulin and maternal diabetes on fetal lipogenesis in the rat

Offspring of diabetic mothers have been investigated with regard to fetal hepatic and brown adipose tissue lipogenesis in the rat. Results, which cannot be explained by existing theory, are obtained from offspring of subdiabetic mothers and manifest diabetic mothers. In re-evaluating the effect of exogenous insulin on perinatal lipogenesis, we find important differences in hormone sensitivity between liver and brown adipose tissue.     

Effect of glycerol and dihydroxyacetone on hepatic lipogenesis

Glycerol is a dietary component which is metabolized primarily by the liver and kidney where it is used mainly for glucose synthesis. The metabolism of glycerol is very similar to that of dihydroxyacetone which can be considered its more oxidized counterpart. The effects of these substrates on hepatic lipogenesis and gluconeogenesis were examined. In isolated hepatocytes, 10 mM dihydroxyacetone caused a large increase in glucose output and stimulated lipogenesis without affecting the lactate/pyruvate ratio or the total ATP content of the cells. (As compared to dihydroxyacetone, 10 mM glycerol was less effective as a gluconeogenic substrate, increased the lactate/pyruvate ratio, caused a slight decrease in the total ATP content, and inhibited lipogenesis by at least 40% depending on the type of diet fed to the rats.) The fall in ATP levels was very small and did not correlate with the changes in fatty acid synthesis. The immediate cause of the inhibition of lipogenesis, brought about by glycerol in hepatocytes from sucrose fed rats, seemed to be a large decrease in pyruvate levels. This did not result from impairment of glycolysis but from a rise in the cytosolic NADH/NAD ratio.     

Effects of maternal fasting on hepatic gluconeogenesis and glucose metabolism in fetal lambs.

In unstressed, normoglycaemic fetal lambs, the liver produces little glucose, and gluconeogenesis is insignificant. Indirect measurements have suggested that the fetus may produce glucose endogenously during hypoglycaemia induced by prolonged maternal starvation. In eight fetal lambs we directly measured total and radiolabelled substrate concentration differences across the liver to determine whether the fetal liver produces glucose after four days of fasting-induced hypoglycaemia. Simultaneously we measured umbilical glucose uptake and fetal glucose utilization. Glucose concentrations in ewes (1.78 +/- 0.44 mmol.-1) and fetuses (0.61 +/- 0.17 mmol.l-1) were decreased. Fetal glucose utilization rate (21.7 +/- 8.9 mumol.min-1.kg-1) was not significantly different from umbilical glucose uptake (17.2 +/- 8.9 mumol.min-1.kg-1). Hepatic glucose production (8.9 +/- 17.2 mumol.min-1.100 g-1) and gluconeogenesis (6.1 +/- 4.4 mumol.min-1.100 g-1) were present, but could account for only 13% and 8% of fetal glucose requirements, respectively. To determine whether glucose output by the fetal liver was limited by substrate availability, we infused lactate, acetate, and acetone into the umbilical veins of four fasted animals, increasing hepatic substrate delivery. Hepatic glucose output did not increase during infusion of gluconeogenic substrates, indicating that substrate availability did not limit gluconeogenesis. We conclude that the gluconeogenic pathway is intact in late-gestation fetal lambs and that the fetal liver is capable of gluconeogenesis. However, the primary change in fetal metabolism during maternal starvation is the reduction in fetal glucose utilization, obviating the need for substantial hepatic glucose production. The factors stimulating this modest increase in fetal hepatic glucose production remain to be elucidated.     

Impact of a cholesterol enriched diet on maternal and fetal plasma lipids and fetal deposition in pregnant rabbits.

Pregnancy is associated with a hypercholesterolemic and a hyperlipidemic state. The totality of the essential fatty acids and 50% of the lipids needed by the fetus are transferred by the placenta from the maternal circulation. The hypothesis of this study is that an augmentation of the maternal plasmatic cholesterol is modifying the fetal lipids accumulation and development during rabbit pregnancy. To demonstrate the impact of a cholesterol enriched diet on plasma lipids during rabbit's pregnancy and on their fetus, we have established two groups: control and hypercholesterolemic rabbits (fed with a 0.2% cholesterol diet). Blood samples were collected before mating and at each trimester of pregnancy for analysis of lipid fractions and their lipoproteins. Plasma analysis shows that starting the 10th day of pregnancy the concentration of total-cholesterol and lipoproteins decreases for both groups. We have demonstrated that for the hypercholesterolemic group, concentrations of total-cholesterol (631%) and lipoproteins are significantly higher at the end of pregnancy than those for the control group. For both groups, after 20 days of pregnancy, triglycerides metabolism was biphasic showing a significant increase followed by a diminution in their concentration. In both groups, free fatty acids increases significantly at the end of the pregnancy (537.5% for the control group and 462.5% for the hypercholesterolemic group). Furthermore, the offsprings of hypercholesterolemic dams manifest a lower birth weight (15.5%) than those of control group. Our results demonstrate that a cholesterol enriched diet modifies greatly the fetal development and lipid metabolism during rabbit's pregnancy. These modifications could be useful for the understanding of the interaction between diet and fetal development in rabbit and probably during human pregnancy.     

Effect of alcoholization upon the maternal and fetal hepatic DNA and the maternal serum-proteins in pregnant albino rats

Experiments were performed on pregnant albino rats (Wistar strain) of 150-200 g b.w. Biochemical investigations involved the determination of maternal and fetal hepatic DNA content (Spirin's method), of maternal serum proteins (total protein content and electrophoretic fractions). The mean litter size, early resorptions, fetal mortality, and some biochemical data of fetuses were also determined. The main statements were as follows: The chronic, peroral administration of 20% ethanol to pregnant albino rats before and during pregnancy induced changes of the biosynthesis of hepatic DNA: a nonsignificant increase as compared with the control group was recorded. The control of serum proteins revealed an increase of the total protein content and of the total electrophoretic serumglobulin fractions. Within the globulin fraction, a hyper-alpha-globulinemia, and a hypo-beta and gamma globulinemia were detected. In the fetuses of the experimental group a slight but statistically significant increase of the hepatic DNA content appeared. In the experimental group the early resorption rate (10.97%) and the fetal mortality (2.43%) was increased in comparison with the control group (0%). In the alcoholized mothers a nonsignificant decrease of the crown-rump length and a significant decrease of fetal and placental weight could be observed.     

Proline and hepatic lipogenesis

The effects of proline on lipogenesis in isolated rat hepatocytes were determined and compared with those of lactate, an established lipogenic precursor. Proline or lactate plus pyruvate increased lipogenesis (measured with 3H2O) in hepatocytes from fed rats depleted of glycogen in vitro and in hepatocytes from starved rats. Lactate plus pyruvate but not proline increased lipogenesis in hepatocytes from starved rats. ( - )-Hydroxycitrate, an inhibitor of ATP-citrate lyase, partially inhibited incorporation into saponifiable fatty acid of 3H from 3H2O and 14C from [U-14C]lactate with hepatocytes from fed rats. Incorporation of 14C from [U-14C]proline was completely inhibited. Similar complete inhibition of incorporation of 14C from [U-14C]proline by ( - )-hydroxycitrate was observed with glycogen-depleted hepatocytes or hepatocytes from starved rats. Inhibition of phosphoenolpyruvate carboxykinase by 3-mercaptopicolinate did not inhibit the incorporation into saponifiable fatty acid of 3H from 3H2O or 14C from [U-14C]proline or [U-14C]lactate. Both 3-mercaptopicolinate and ( - )-hydroxycitrate increased lipogenesis (measured with 3H2O) in the absence or presence of lactate or proline with hepatocytes from starved rats. The results are discussed with reference to the roles of phosphoenolpyruvate carboxykinase, mitochondrial citrate efflux, ATP-citrate lyase and acetyl-CoA carboxylase in proline- or lactate-stimulated lipogenesis.     

Effect of prolonged ethanol ingestion on hepatic lipogenesis and related enzyme activities

1. Hepatic lipogenesis in vivo and the activities of enzymes associated with fatty acid synthesis in the liver were studied in rats fed for 21 days on liquid diets containing ethanol. 2. The ethanol-fed rats developed a moderate hepatic triacylglycerol accumulation during this period. When carbohydrate was replaced by ethanol in the diet, the rate of fatty acid synthesis was slower in the ethanol-fed rats on low-, medium- and high-fat diets than in the appropriate controls. However, when the fat/carbohydrate ratio was kept the same in the ethanol-fed and control rats, ethanol had no influence on the rate of fatty acid synthesis. 3. Glucose 6-phosphate dehydrogenase activity was lower in the ethanol-fed group. ;Malic' enzyme activity did not change during the ethanol treatment when the fat/carbohydrate ratio was kept unchanged. 4. The ATP citrate lyase activity was lower in the ethanol-fed rats on all diets, whereas acetyl-CoA synthetase activity was independent of the composition of the control diet, but was lower in the ethanol-fed rats, in which the concentration of the active form of pyruvate dehydrogenase was also lower. 5. It is concluded that hepatic fatty acid synthesis does not play any major role in ethanol-induced triacylglycerol accumulation. Careful design of the diets is necessary to reveal the specific effects of ethanol on the enzymes associated with lipogenesis.     

Effect of maternal restraint stress on fetal development of ICR mice.

The present study was conducted to elucidate the susceptibility of embryos and fetuses at different gestational stages to the maternal stress in mice. Groups of pregnant ICR mice were subjected to daily 12-h restraint stress, taped in the supine position on a plastic board, on gestational days (GD) 1-4, 5-8, 9-12 and 13-16, respectively. Caesarean sections were performed on gestational day 18, and the fetuses were weighed and examined for morphological defects. During the daily restraint for 4 days, the maternal body weights markedly decreased. Although the body weights recovered gradually after termination of the stress, the recovery was not full until the final stage of pregnancy. Interestingly, restraint stress caused growth retardation of the fetuses, leading to a significant decrease in their body weights, and increased early and late resorptions of embryos and fetuses according to the stress periods. Although the preceding (GD1-4) and concurrent (GD5-8) stresses did not affect embryonic implantation, restraint stress on GD9-12 caused cleft palate. Whereas vertebral abnormalities, mainly bipartite ossification, were observed only in animals stressed on GD5-8, abnormalities of sternebrae, exhibiting asymmetric or bipartite ossification, were enhanced by the stress at all of the gestational stages. On the other hand, the incidence of other malformations including renal malposition and costal abnormalities was not increased by stress at any of the 4 stages. Taken together, the results suggest that intensive restraint stress influences the maternal body weight resulting in growth retardation and increased mortality of embryos and fetuses, in addition to gestational stage-specific ventricular dilatation, cleft palate and sternal abnormalities.     

Effect of maternal thyroparathyroidectomy before gestation on fetal development in rats.

Female rats were thyroparathyroidectomized (TPTX) at 24 (immature), 40 (pubertal) and 75 (matured) days of age, at least 21 days before mating. Thyroxine (2.5 microgram/kg) or parathyroid hormone (150 USP units/kg x 2) was replaced in two TPTX groups. Thyroxine deficient groups of all ages had reduced body weight, litter size and serum thyroxine and calcium level. Fetal weights at 20 days of gestation in all thyroxine deficient groups were significantly reduced but placental weight was generally increased. Maternal serum thyroxine and fetal weight was positively related when all groups were taken together, but maternal serum calcium and fetal weight was not related. There were no significant differences in gross, visceral or skeletal anomalies in the fetuses in any group.     

Effect of dexamethasone on fetal hepatic glutamine-glutamate exchange

Intravenous infusion of dexamethasone (Dex) in the fetal lamb causes a two- to threefold increase in plasma glutamine and other glucogenic amino acids and a decrease of plasma glutamate to approximately one-third of normal. To explore the underlying mechanisms, hepatic amino acid uptake and conversion of L-[1-(13)C]glutamine to L-[1-(13)C]glutamate and (13)CO(2) were measured in six sheep fetuses before and in the last 2 h of a 26-h Dex infusion. Dex decreased hepatic glutamine and alanine uptakes (P < 0.01) and hepatic glutamate output (P < 0.001). Hepatic outputs of the glutamate (R(Glu,Gln)) and CO(2) formed from plasma glutamine decreased to 21 (P < 0.001) and 53% (P = 0.009) of control, respectively. R(Glu,Gln), expressed as a fraction of both outputs, decreased (P < 0.001) from 0.36 +/- 0.02 to 0.18 +/- 0.04. Hepatic glucose output remained virtually zero throughout the experiment. We conclude that Dex decreases fetal hepatic glutamate output by increasing the routing of glutamate carbon into the citric acid cycle and by decreasing the hepatic uptake of glucogenic amino acids.     

Effect of maternal malnutrition on surface activity of fetal lungs in rats.

The effects of maternal malnutrition on fetal lung growth and surface forces were studied in albino rats. Pregnant albino rats were subjected to one of the following diets: rat chow ad lib. (controls), partial food deprivation (intake one-half that of the controls), complete food deprivation for 4 days (on gestation day 3-7, 9-13, or 17-21), low protein (8%), and fat free. The fetal lungs were studied on the 21st day of gestation (delivered by cesarean section) or at birth (gestation day 22). Fetuses and neonates after maternal food deprivation (FD) on the 17-21 day of pregnancy, and after a low-protein (LP) diet during pregnancy, had significantly smaller body weight and lung wet or dry weight/body weight ratio (hypocellular lungs). The minimum surface tension (gamma min) of fetal lung extracts was significantly increased with FD and LP. This was associated with a reduction of about 35% in lung lecithin content, expressed per lung DNA. The earlier in pregnancy the rat was subjected to 4-day food deprivation the less the effect on the fetus. At birth the gamma min and the lung lecithin content reached control values. This recovery occurred after birth (at age 4-10 h) and prior to first feeding. However, the lungs remained small and hypocellular. The results indicate that the nutritional status of the pregnant rat influences the surface activity and the growth of the fetal lung.     

Effect of a linseed diet on lipogenesis, fatty acid composition and stearoyl-CoA-desaturase in rabbits

The aim of the study was to examine the effect of a linseed diet on meat quality and on lipogenesis in rabbits. Twelve rabbits were fed a control or a linseed diet. There was no diet effect on growth, food consumption, carcass characteristics and meat ultimate pH and colour. Feeding the linseed diet increased the n-3 polyunsaturated fatty acids (PUFA) levels in perirenal and interscapular fats, in the Longissimus dorsi muscle and in the liver. The linseed diet produced lower linoleic acid/α-linolenic acid ratios in adipose tissues and in the Longissimus dorsi muscle, but not in the liver. Diet did not affect lipogenic enzyme activities in the Longissimus dorsi muscle, whereas the linseed diet decreased the lipogenic potential in perirenal and interscapular fats, and in the liver. Feeding rabbits with a high n-3 PUFA diet led to a decrease in the oxidative stability of perirenal fat and the Longissimus dorsi muscle, and to an inhibition of stearoyl-CoA-desaturase activity in liver and in adipose tissues, but not in muscle.     

Stearolyl-CoA desaturase: a control enzyme in hepatic lipogenesis.

1. Hepatocytes were isolated by perfusion of the liver with collagenase/salt solutions and incubated in culture after attachment to plastic culture dishes for periods up to 48 h. 2. The cells, when incubated in serum-free culture medium in the presence of insulin, showed enhanced stearolyl-CoA desaturase activity which was not observed when 50 muM cycloheximide was included. When insulin was omitted from the medium, the cells lost 80% of their original desaturase activity. 3. Cells isolated from animals fed 20% (w/w) sucrose for two weeks prior to sacrifice, showed high levels of fatty acid synthesis, stearolyl-CoA desaturase activity and triacylglycerol synthesis when compared with cells isolated from animals fed a corn oil supplemental diet. 4. The observations are discussed in terms of the influence of stearoyl-CoA desaturase activity on hepatic lipogenesis.     

Effect of maternal hypercholesterolemia on fetal sterol metabolism in the Golden Syrian hamster.

The fetus obtains a significant amount of cholesterol from de novo synthesis. Studies have suggested that maternal cholesterol may also contribute to the cholesterol accrued in the fetus. Thus, the present studies were completed to determine whether diet-induced maternal hypercholesterolemia would affect fetal sterol metabolism. To accomplish this, maternal plasma cholesterol concentrations were increased sequentially by feeding hamsters 0.0%, 0.12%, 0.5%, and 2.0% cholesterol. At 11 days into a gestational period of 15.5 days, cholesterol concentrations and sterol synthesis rates were measured in the three fetal tissues: the placenta, yolk sac, and fetus. In the placenta and yolk sac, the cholesterol concentration increased significantly when dams were fed as little as 0.12% cholesterol (P < 0.0167), and sterol synthesis rates decreased in dams fed at least 0.5% or 2% cholesterol, respectively (P < 0.0167). In the fetus, changes in fetal cholesterol concentration and sterol synthesis rates occurred only when dams were fed at least 0.5% cholesterol, which corresponded to a greater than 2-fold increase in maternal plasma cholesterol concentrations. When the cholesterol concentration in the fetal tissues in each animal was plotted as a function of maternal plasma cholesterol concentration, a linear relationship was found (P < 0.001).These studies demonstrate that sterol homeostasis in fetal tissues, including the fetus, is affected by maternal plasma cholesterol concentration in a gradient fashion and that sterol metabolism in the fetus is dependent on sterol homeostasis in the yolk sac and/or placenta.     

Effects of the diet consumed during the pregnancy on the lipids content in maternal and fetal rat lungs.

This study was designed to determine if the quantity of lipids in the diet fed to pregnant rats would affect the deposition of fat in the fetal lung. Wistar rats were fed with two different diets during pregnancy: Standard Diet (StD; 4.000 cal/g) and High Fat Carbohydrate Free Diet (HFCFD; 6.000 cal/g). The rats consumed daily the same amount of calories from these different diets. The concentrations of triglycerides (TG), phospholipids (PL), total, esterified and free cholesterol (TC, EC and FC, respectively) were determined in serum and lung from pregnant rats as well as from their 19 day old fetuses. In the serum of rats fed with HFCFD, the cholesterol concentration increased in relation to that of rats fed with StD. In pregnant rat lung, the PL concentrations decreased and the TC, EC and FC concentrations increased with HFCFD in relation to StD. The triglycerides were not modified in any case. The lipidic composition of the sera and fetal lung were not changed by the two diets consumed by pregnant rats. This may be a biological protective mechanism to assure an adequate synthesis of alveolar surfactant.     

Effect of maternal ethanol consumption on foetal and neonatal rat hepatic protein synthesis.

Effects of maternal ethanol consumption were investigated on the rates of protein synthehsis by livers of foetal and neonatal rats both in vivo and in vitro, and on the activities of enzymes involved in protein synthesis and degradation. The rates of general protein synthesis by ribosomes in vitro studied by measuring the incorporation of [14C]leucine into ribosomal protein showed that maternal ethanol consumption resulted in an inhibition of the rates of protein synthesis by both foetal and neonatal livers from the ethanol-fed group. The rates of incorporation of intravenously injected [14C]leucine into hepatic proteins were also significantly lower in the foetal, neonatal and adult livers from the ethanol-fed group. Incubation of adult-rat liver slices with ethanol resulted in an inhibition of the incorporation of [14C]leucine into hepatic proteins; however, this effect was not observed in the foetal liver slices. This effect of externally added ethanol was at least partially prevented by the addition of pyrazole to the adult liver slices. Pyrazole addition to foetal liver slices was without significant effect on the rates of protein synthesis. Cross-mixing experiments showed that the capacity of both hepatic ribosomes and pH5 enzyme fractions to synthesize proteins was decreased in the foetal liver from the ethanol-fed group. Maternal ethanol consumption resulted in a decrease in hepatic total RNA content, RNA/DNA ratio and ribosomal protein content in the foetal liver. Foetal hepatic DNA content was not significantly affected. Ethanol consumption resulted in a significant decrease in proteolytic activity and the activity of tryptophan oxygenase in the foetal, neonatal and adult livers. It is possible that the mechanisms of inhibition of protein synthesis observed here in the foetal liver after maternal ethanol consumption may be responsible for at least some of the changes observed in 'foetal alcohol syndrome'.