Hepatic metabolism of [1-14C]oleate in pregnancy

The effect of iron deficiency on the temporal changes in the expression of genes associated with fat metabolism in the pregnant rat

Iron is essential for the oxidative metabolism of lipids. Lipid metabolism changes during gestation to meet the requirements of the growing fetus and to prepare for lactation. The temporal effects of iron deficiency during gestation were studied in female rats fed complete or iron‐deficient diets. Plasma triglycerides were elevated in the iron‐deficient group throughout gestation. There were time‐dependent changes in the triglyceride content of the maternal liver, falling at the midpoint of gestation and then increasing on d21.5. Compared to the control, triglycerides in the maternal liver were not different in the iron‐deficient group prior to pregnancy and on d12.5, but were markedly reduced by d21.5. The abundance of mRNAs in the maternal liver suggests that lipogenesis is unchanged and beta‐oxidation is reduced on d21.5 by iron deficiency. On d21.5 of gestation, the expression of placental lipase was unchanged by iron deficiency, however, the abundance of mRNAs for SREBP‐1c, FABP4 were reduced, suggesting that there were changes in fatty acid handling. In the fetal liver, iron deficiency produced a marked decrease in the abundance of the L‐CPT‐1 mRNA, suggesting that beta‐oxidation is reduced. This study shows that the major effect of iron deficiency on maternal lipid metabolism occurs late in gestation and that perturbed lipid metabolism may be a common feature of models of fetal programming.

High Fat Diet Administration during Specific Periods of Pregnancy Alters Maternal Fatty Acid Profiles in the Near-Term Rat

Excessive fat intake is a global health concern as women of childbearing age increasingly ingest high fat diets (HFDs). We therefore determined the maternal fatty acid (FA) profiles in metabolic organs after HFD administration during specific periods of gestation. Rats were fed a HFD for the first (HF1), second (HF2), or third (HF3) week, or for all three weeks (HFG) of gestation. Total maternal plasma non-esterified fatty acid (NEFA) concentrations were monitored throughout pregnancy. At day 20 of gestation, maternal plasma, liver, adipose tissue, and placenta FA profiles were determined. In HF3 mothers, plasma myristic and stearic acid concentrations were elevated, whereas docosahexaenoic acid (DHA) was reduced in both HF3 and HFG mothers. In HF3 and HFG mothers, hepatic stearic and oleic acid proportions were elevated; conversely, DHA and linoleic acid (LA) proportions were reduced. In adipose tissue, myristic acid was elevated, whereas DHA and LA proportions were reduced in all mothers. Further, adipose tissue stearic acid proportions were elevated in HF2, HF3, and HFG mothers; with oleic acid increased in HF1 and HFG mothers. In HF3 and HFG mothers, placental neutral myristic acid proportions were elevated, whereas DHA was reduced. Further, placental phospholipid DHA proportions were reduced in HF3 and HFG mothers. Maintenance on a diet, high in saturated fat, but low in DHA and LA proportions, during late or throughout gestation, perpetuated reduced DHA across metabolic organs that adapt during pregnancy. Therefore a diet, with normal DHA proportions during gestation, may be important for balancing maternal FA status.

Decreased nuclear hormone receptor expression in the livers of mice in late pregnancy

During the third trimester of pregnancy, there is an increase in serum triglyceride and cholesterol levels. The mechanisms accounting for these changes in lipid metabolism during pregnancy are unknown. We hypothesized that, during pregnancy, the expression of nuclear hormone receptors involved in regulating lipid metabolism would decrease. In 19-day pregnant mice, serum triglyceride and non-HDL cholesterol levels were significantly increased, whereas total cholesterol was slightly decreased, because of a decrease in the HDL fraction. Peroxisome proliferator-activated receptor (PPAR)alpha, PPARbeta/delta, and PPARgamma, liver X receptor (LXR)alpha and LXRbeta, farnesoid X receptor (FXR), and retinoid X receptor (RXR)alpha, RXRbeta, and RXRgamma mRNA levels were significantly decreased in the livers of 19-day pregnant mice. Additionally, the expressions of thyroid receptor (TR)alpha, pregnane X receptor, sterol regulatory element-binding proteins (SREBP)-1a, SREBP-1c, SREBP-2, and liver receptor homolog 1 were also decreased, whereas the expression of TRbeta, constitutive androstane receptor, and hepatic nuclear factor 4 showed no significant change. mRNA levels of the PPAR target genes carnitine-palmitoyl transferase 1alpha and acyl-CoA oxidase, the LXR target genes SREBP1c, ATP-binding cassettes G5 and G8, the FXR target gene SHP, and the TR target genes malic enzyme and Spot14 were all significantly decreased. Finally, the expressions of PPARgamma coactivator (PGC)-1alpha and PGC-1beta, known activators of a number of nuclear hormone receptors, were also significantly decreased. The decreases in expression of RXRs, PPARs, LXRs, FXR, TRs, SREBPs, and PGC-1s could contribute to the alterations in lipid metabolism during late pregnancy.

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.

A cholesterol-rich diet causes a greater hypercholesterolemic response in pregnant than in nonpregnant rats and does not modify fetal lipoprotein profile

To determine whether pregnancy modifies the hyperlipidemic response to a cholesterol-rich diet, pregnant and virgin rats were fed a semisynthetic diet supplemented (CRD) or not (CD) with 2% cholesterol and 1% cholic acid and studied at d 20 of treatment and/or gestation. Plasma triglycerides, free fatty acids and glycerol and liver triglycerides were greater in pregnant than in virgin rats fed CRD. The increase in both plasma and liver cholesterol caused by CRD did not differ in the two groups. In rats fed CD, hepatic lipase activity in liver was lower in pregnant than in virgin rats, while in those fed CRD, virgin rats had lower activity than those fed CD. Plasma VLDL-triglycerides were higher and LDL-triglycerides lower in pregnant than in virgin rats fed CD. Among those fed CRD, pregnant rats had a higher triglyceride concentration in VLDL and HDL than virgin rats. Cholesterol concentration was higher in VLDL and IDL and lower in HDL in both groups fed CRD than in those fed CD, while cholesterol level in LDL was higher only in pregnant rats fed CRD than in those fed CD. Whereas placental cholesterol concentration was higher in pregnant rats fed CRD than CD, maternal CRD intake did not modify fetal plasma lipoprotein concentrations, fetal body weight or litter size, indicating a lack of cholesterol transfer by the rat placenta. Results therefore show a greater responsiveness to CRD in pregnant than in virgin rats, and we propose that CRD promotes greater liver VLDL-production and lower LDL removal in pregnant than in virgin rats.

Expression of fatty acid binding protein in the liver during pregnancy and lactation in the rat

Expression of the liver fatty acid binding protein (L-FABP) has been studied in the liver of pregnant and lactating rats. The L-FABP concentration found in the cytosol by immuno-enzymatic assay (ELISA) was consistently higher in the dams during the pregnancy and the lactation than in the age-matched virgin females. Paradoxically, a decrease in the L-FABP mRNA level occurred in the maternal liver during the last days of the gestation. This level remained low on days 7 and 14 of the lactation. Since the transcription rate of the L-FABP gene was unchanged in the maternal liver, these data suggest a post-transcriptional regulation of the L-FABP during pregnancy and lactation in the rat. The nutritional adaptations occurring during pregnancy and lactation are not involved in this regulation since a chronic maternal food-restriction failed to correct these modifications. The mechanism of this regulation is presently unknown, but possibilities include hormonally mediated effects.

Effect of starvation on lipoprotein lipase activity in different tissues during gestation in the rat

This study was addressed to determine whether the tissue-specific LPL activity response to fasting differs between nonpregnant and pregnant rats over the course of pregnancy. Fed and 24-h fasted rats were studied at days 12, 15 or 20 of gestation and were compared to virgin controls. In fed rats at days 15 and 20 of gestation LPL activity decreased in lumbar adipose tissue and the heart and liver, and increased in mammary gland tissue. Fasting decreased LPL activity in lumbar adipose tissue in 12 day pregnant and virgin rats and in mammary gland tissue in pregnant rats at 15 and 20 days of gestation and in virgin rats, whereas it increased LPL activity in heart tissue in rats at day 15 and 20 and in liver at day 20 of gestation. Plasma triacylglycerols were higher in 20 day pregnant rats than in the other groups when fed and this difference was even more noticeable in the fasting condition where the plasma beta-hydroxybutyrate level also reached the highest value in the 20 day pregnant rats. Since tissue LPL activity controls the hydrolysis and uptake of circulating triacylgylcerols, the present results indicate that in fed rats after the 15th day of gestation circulating triacylglycerols are preferentially taken up by the mammary gland instead of being taken up by adipose tissue and heart. However, after fasting, circulating triacylglycerols are driven to the heart and liver in the late pregnant rat, and become a major source for fatty acid oxidation, an effect that seems to be specially evident in the liver of the 20 day pregnant rat where there is an intense increase in LPL activity and the triacylglycerols become preferential substrates for ketone body production.

Changes in cholesteryl ester transfer protein activity during normal gestation and postpartum

Cholesteryl ester transfer protein (CETP) activity was measured in a d > 1.21 kg/L plasma fraction collected from healthy women at different times during gestation, postpartum, and in control women. CETP activity was highest in the second trimester of gestation, declined at the third trimester, and was lowest at postpartum. Only the value at the second trimester was significantly different from that of control women. This trend differed from that of circulating lipoproteins: very low-density lipoprotein (VLDL)-lipids, including triglycerides and cholesterol, increased progressively from the first to the third trimester, and then declined at postpartum. Low-density lipoprotein (LDL)-cholesterol levels, like VLDL levels, rose during gestation but then remained elevated at postpartum. High-density lipoprotein (HDL)-cholesterol as well as HDL-phospholipids and apolipoprotein A-I, peaked in the second trimester, remaining elevated in the third trimester and then fell at postpartum. Finally, HDL-triglyceride increased markedly from the first to the second trimester, rose somewhat higher during the third trimester, and declined at postpartum. When all the samples from pregnant women were considered together, CETP activity correlated significantly with HDL-triglyceride levels and the changes in CETP activity during gestation and postpartum paralleled those of the HDL-triglyceride/VLDL-triglyceride ratio. These results suggest that CETP contributes to the exaggerated accumulation of triglycerides in HDL that begins in the second trimester of human gestation.

Gestational hyperlipidemia in the rat is characterized by accumulation of n - 6 and n - 3 fatty acids, especially docosahexaenoic acid

We have evaluated the relative and quantitative changes in long-chain fatty acids in maternal liver, serum, carcass and conceptus (fetuses plus placentae) during pregnancy in the rat, to ascertain whether previous concern over lower proportions of n - 6 and n - 3 fatty acids in maternal serum could be indicative of suboptimal n - 6 or n - 3 fatty acid status. Gestational hyperlipidemia was characterized by proportional decreases in linoleic, stearic and arachidonic acids but increases in palmitic and docosahexaenoic acids. However, the quantitative amount (microgram/ml) of linoleic, arachidonic and docosahexaenoic acids in serum lipids actually increased 2-5-fold from mid-pregnancy to term. Compared to non-pregnant rats, gestational hyperlipidemia was also associated with a lower proportion but similar quantity of linoleic acid in maternal carcass and adipose stores. We conclude that gestational hyperlipidemia in the rat is characterized by a relative but not quantitative decrease in whole-body stores of n - 6 fatty acids and a marked proportional and quantitative increase in docosahexaenoic acid in maternal organs and in the conceptus.

Appearance of circulating and tissue 14C-lipids after oral 14C-tripalmitate administration in the late pregnant rat

Studies were performed to determine whether and/or how dietary lipids participate in maternal hypertriglyceridemia during late gestation in the rat. After oral administration of glycerol-tri(1-14C)-palmitate, total radioactivity in plasma increased more rapidly in 20-day pregnant rats than in either 19-day pregnant rats or virgin controls. At the peak of plasma radioactivity, four hours after the tracer was administered, most of the plasma label corresponded to 14C-lipids in triglyceride-rich lipoproteins (d less than 1.006), and when expressed per micromol of triglyceride, values were higher in pregnant than in virgin rats. The difference was less after 24 hours, although at this time the level of 14C-lipids in d less than 1.006 lipoproteins was still higher in 20-day pregnant rats than in virgins. Tissue 14C-lipids, as expressed per gram of fresh weight, were similar in pregnant and virgin rats, but the values in mammary glands were much higher in the former group. Estimated recovery of administered radioactivity four hours after tracer in total white adipose tissue, mammary glands, and plasma lipids was higher in pregnant than in virgin rats. No difference was found between 20-day pregnant and virgin rats either in the label retained in the gastrointestinal tract or in that exhaled as 14C-CO2 during the first four hours following oral administration of 14C-tripalmitate. These findings plus the known maternal hyperphagia, indicate that in the rat at late pregnancy triglyceride intestinal absorption is unchanged or even enhanced and that dietary lipids actively contribute to both maternal hypertriglyceridemia and lipid uptake by the mammary gland.

Comparative utilization of glycerol and alanine as liver gluconeogenic substrates in the fed late pregnant rat

The appearance of plasma [14C]glucose in the inferior cava vein after a pulse of 0.2 mmol of [U-14C]L-alanine or [U-14C]glycerol/200 g body wt given through the portal vein was studied in fed 21 day pregnant rats and virgin controls under pentobarbital anesthesia. In both groups values were much higher when [U-14C]glycerol was the administered tracer than when [U-14C]L-alanine, and they were augmented in pregnant versus virgin animals at 1 min when receiving [U-14C]glycerol and at 2 min when receiving [U-14C]L-alanine. 20 min after the tracers rats receiving [U-14C]glycerol showed much higher liver [14C]glycogen and [14C]glyceride glycerol than those receiving [U-14C]L-alanine. Radioactivity present in liver as [14C]glyceride glycerol was greater in pregnant than in virgin rats receiving [U-14C]glycerol whereas radioactivity corresponding to [14C]fatty acids was lower in the former group receiving either tracer. At 20 min after maternal treatments fetuses showed lower plasma [14C]glycerol than [14C]alanine values but plasma [14C]glucose and liver [14C]glycogen values were much greater in fetuses from mothers receiving [U-14C]glycerol than [U-14C]L-amine. Besides showing the higher gluconeogenic efficiency in pregnant than in virgin rats, results indicate that at late gestation glycerol is used as a preferential substrate for both glucose and glyceride glycerol synthesis in liver.

The effect of altered thyroid status on lipid metabolism in Nubian goats

The effects of triiodothyronine (T3)-induced hyperthyroidism and of carbimazole (CZ)-produced hypothyroidism on lipid metabolism were studied in Nubian goats (Capra hircus). T3 treatment decreased the serum, liver and heart triglyceride, cholesterol and phospholipid concentrations. These changes were accompanied by an increase in the activity of lipoprotein lipase (LPL) in the heart and skeletal muscles. CZ treatment at a dose of 90 mg/goat significantly increased the serum triglyceride, liver cholesterol and heart phospholipid. CZ treatment significantly increased the liver and heart triglyceride concentration but the activity of LPL was not affected.

Response to starvation of hepatic carnitine palmitoyltransferase activity and its regulation by malonyl-CoA. Sex differences and effects of pregnancy

1. Hepatic carnitine palmitoyltransferase activity was measured over a range of concentrations of palmitoyl-CoA and in the presence of several concentrations of the inhibitor malonyl-CoA. These measurements were made in mitochondria obtained from the livers of fed and starved (24 h) virgin female and fed and starved pregnant rats. 2. In the fed state overt carnitine palmitoyltransferase activity was significantly lower in virgin females than in age-matched male rats. 3. Starvation increased overt carnitine palmitoyltransferase activity in both virgin and pregnant females. This increase was larger than in the male and was greater in pregnant than in virgin females. 4. In the fed state pregnancy had no effect on the Hill coefficient or the [S]0.5 when palmitoyl-CoA was varied as substrate. Pregnancy did not alter the sensitivity of the enzyme to inhibition by malonyl-CoA. 5. Starvation decreased the sensitivity of the enzyme to malonyl-CoA. The change in sensitivity was similar in male, virgin female and pregnant rats. 6. The possible relevance of these findings to known sex differences and changes with pregnancy in hepatic fatty acid oxidation and esterification are discussed.

Plasma unesterified fatty acid and triacylglycerol concentration of the goat (Capra hircus) during pregnancy and lactation

1. The concentrations of unesterified fatty acids and triacylglycerol were measured in plasma obtained from goats at various stages of pregnancy and lactation. 2. The plasma unesterified fatty acid concentration increased during the last third of pregnancy: highest concentrations were found at parturition and during early lactation. 3. The plasma triacylglycerol concentration showed a transient increase during mid-pregnancy: the concentration fell around parturition and no evidence for hypertriglyceridemia was found during late-pregnancy. 4. Results are compared with those of other studies of ruminant and non-ruminant species.

Regulation of hepatic fatty acid metabolism. The activities of mitochondrial and microsomal acyl-CoA:sn-glycerol 3-phosphate O-acyltransferase and the concentrations of malonyl-CoA, non-esterified and esterified carnitine, glycerol 3-phosphate, ketone bodies and long-chain acyl-CoA esters in livers of fed or starved pregnant, lactating and weaned rats

1. The concentrations of malonyl-CoA, glycerol 3-phosphate, non-esterified carnitine, acid-soluble and acid-insoluble acylcarnitines, acetoacetate, 3-hydroxybutyrate and acid-insoluble acyl-CoA were measured in rapidly-frozen liver samples from fed or starved (24h) virgin, pregnant (19-20 days), lactating (2, 10-12 and 18-20 days) and weaned (for 24h, on 10th day of lactation) rats. The activities of total and N-ethylmaleimide-sensitive and -insensitive glycerophosphate acyltransferase (acyl-CoA:sn-glycerol 3-phosphate O-acyltransferase; EC 2.3.1.15) were also measured. 2. The concentration of malonyl-CoA was significantly higher in liver of fed pregnant, mid- and late-lactating rats than in liver of fed virgin rats. After starvation for 24h hepatic malonyl-CoA concentrations were higher in mid-lactating rats and lower in pregnant and weaned rats than in virgin animals. 3. After starvation for 24h the hepatic concentrations of glycerol 3-phosphate, ketone bodies, acid-soluble acylcarnitines and the value for the [3-hydroxybutyrate]/[acetoacetate] ratio were all highest in pregnant rats, intermediate in virgin, 2-day lactating and weaned animals and lowest in mid- and late-lactating rats. The concentrations of acid-insoluble acylcarnitines also increased most in pregnant rats, after starvation. The concentration of acid-insoluble acyl-CoA increased equally after starvation in virgin and pregnant animals but did not increase significantly in all other animals studied. 4. The total concentration of carnitine was similar in livers of fed virgin, pregnant and 2-day lactating animals but fell markedly by the 10th day of lactation and remained low in late-lactating animals. The concentration of non-esterified carnitine followed the same pattern. After starvation for 24h the hepatic concentration of non-esterified carnitine decreased significantly in virgin, pregnant and 2-day lactating animals, but remained unchanged in mid- and late-lactating or weaned animals. 5. The activities of N-ethylmaleimide-sensitive and -insensitive glycerophosphate acyltransferase both increased significantly in livers of mid-lactating animals. After starvation for 24h the activity of the N-ethylmaleimide-insensitive O-acyltransferase decreased in livers of virgin, pregnant and mid-lactating animals, whereas the activity of the N-ethylmaleimide-sensitive O-acyltransferase was unchanged in virgin animals but decreased markedly in livers of pregnant and lactating rats. 6. The results are discussed in relation to the importance of different metabolic parameters in the regulation of long-chain acyl-CoA metabolism in the liver.