Body composition and fat distribution during the first 2 weeks of gestation in ad lib.-fed and energy-restricted rats

Changes in hepatic triglyceride content with the activation of ER stress and increased FGF21 secretion during pregnancy

Background

To meet the needs of foetal growth and development, marked changes in lipid profiles occur during pregnancy. Abnormal lipid metabolism is often accompanied by adverse pregnancy outcomes, which seriously affect maternal and infant health. Further understanding of the mechanism of lipid metabolism during pregnancy would be helpful to reduce the incidence of adverse pregnancy outcomes.

Methods

Pregnant mice were euthanized in the virgin (V) state, on day 5 of pregnancy (P5), on day 12 of pregnancy (P12), on day 19 of pregnancy (P19) and on lactation day 2 (L2). Body weight and energy expenditure were assessed to evaluate the general condition of the mice. Triglyceride (TG) levels, the cholesterol content in the liver, liver histopathology, serum lipid profiles, serum β-hydroxybutyrate levels, fibroblast growth factor-21 (FGF21) levels and the levels of relevant target genes were analysed.

Results

During early pregnancy, anabolism was found to play a major role in liver lipid deposition. In contrast, advanced pregnancy is an overall catabolic condition associated with both increased energy expenditure and reduced lipogenesis. Moreover, the accumulation of hepatic TG did not appear until P12, after the onset of endoplasmic reticulum (ER) stress on P5. Then, catabolism was enhanced, and FGF21 secretion was increased in the livers of female mice in late pregnancy. We further found that the expression of sec23a, which as the coat protein complex II (COPII) vesicle coat proteins regulates the secretion of FGF21, in the liver was decreased on P19.

Conclusion

With the activation of ER stress and increased FGF21 secretion during pregnancy, the hepatic TG content changes, suggesting that ER stress and FGF21 may play an important role in balancing lipid homeostasis and meeting maternal and infant energy requirements in late pregnancy.

Possible effects of pollock and herring on the growth and reproductive success of Steller sea lions (Eumetopias jubatus): insights from feeding experiments using an alternative animal model, Rattus norvegicus

The decline of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska appears to have been associated with a switch of diet from one dominated by fatty forage fishes (such as herring; Clupea pallasi) to one dominated by low-fat fish (such as pollock; Theragra chalcogramma). Observations made during the decline include reduced body size of sea lions, low pregnancy rates, and high mortality. We used the general mammalian model, the laboratory rat (Rattus norvegicus), to test whether changing the quality of prey consumed could cause changes in size and reproductive performance. Five groups of twelve female, weanling rats were fed diets composed of herring (H), pollock (P), pollock supplemented with herring oil (PH), pollock supplemented with pollock oil (PP), or a semi-purified diet (ICN). Mean body weights were greatest for H, followed by PH, P, PP and finally ICN, although ICN was the only group significantly different from the others (P<0.05). Food intakes before mating were 10 % higher for groups on the lower-fat diets (P and ICN), resulting in similar energy intakes in all groups. The protein efficiency ratio was highest for the H diet, slightly lower for all pollock diets, and significantly lower for ICN (P<0.05). The fetal weights for mothers fed P were significantly reduced (P<0.05). The present study shows that the energy content was a major limiting factor in the nutritional quality of pollock. When food intake was adjusted to meet energetic requirements, there were no detrimental consequences from eating pollock. However, supplementation of pollock meal with additional pollock oil may reduce growth and reproductive performance, although the reasons for this were not apparent.

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.

Maternal nutrition affects the ability of treatment with IGF-I and IGF-II to increase growth of the placenta and fetus, in guinea pigs

The aim of this study was to investigate how administration of IGF-I and IGF-II, during early to mid pregnancy, affects maternal growth and body composition as well as fetal and placental growth, in ad libitum fed, and in moderately, chronically food restricted guinea pigs. From day 20 of gestation, mothers (3-4 months old) were infused with IGF-I, IGF-II (565 microg/day) or vehicle for 17 days and then killed on day 40 of gestation. Maternal organ weights, fetal and placental weights were assessed. Treatment with IGFs did not alter body weight gain and had small effects on body composition in the mothers. Both IGF-I and IGF-II increased fetal and placental weights in ad libitum fed dams and IGF-I increased placental weight in food restricted dams. In conclusion, treatment with IGF-I during the first half of pregnancy stimulates placental growth in both ad libitum fed and food restricted guinea pigs without affecting maternal growth while fetal growth is stimulated by IGF treatment only in ad libitum fed animals.

Food restriction alters pregnancy-associated changes in IGF and IGFBP in the guinea pig

The effect of moderate food restriction on pregnancy-associated changes in weight gain, body composition, and circulating insulin-like growth factors (IGF) I and II and IGF-binding proteins (IGFBP)-1 through-4 and their relationship was determined in the guinea pig. Pregnancy did not stimulate weight gain but reduced fat deposition in ad libitum-fed animals and increased weight gain and fat deposition in food-restricted animals relative to their respective virginal group. Pregnancy increased the abundance of circulating IGF-I regardless of food intake and increased that of IGF-II in food-restricted animals only. Pregnancy also increased circulating IGFBP-1 and -2 in ad libitum-fed and food-restricted animals and IGFBP-4 in ad libitum-fed animals. Multiple regression analysis showed that maternal weight gain was negatively associated with circulating IGF-II and IGFBP-2. Fetal weight was positively associated with maternal circulating IGF-II and negatively associated with maternal circulating IGFBP-1 and -2. Significant interactions indicate, however, that the role of IGF-II and IGFBP-1 on fetal growth is dependent on the nutritional status of the mother.

Consumption of a high fat diet impairs reproductive performance in Sprague-Dawley rats

Rats made obese by cafeteria feeding have poor reproductive outcomes. To investigate this phenomenon in animals fed a more nutritionally adequate diet, female rats were fed either a high fat (HF) (modified AIN-76A, 35 g fat/100 g diet) or a control (C) (AIN-76A, 5 g fat/100 g diet), diet, beginning at 27 d of age. To assess reproductive performance, rats were studied at d 0, 5 and 18 of pregnancy and on d 3 of lactation. Pregnancy rates were significantly (P < 0.001) lower in the high fat-fed rats than in the control-fed rats (56.4 and 89.1%, respectively). There was no difference between groups in total pregnancy weight gain or the proportion of weight gained during pregnancy that was retained by the dam. High fat-fed dams tended to gain weight more rapidly early in gestation than control-fed dams and then less rapidly than control-fed dams during the last week of gestation. Litter number and pup weight at birth did not differ between groups, but of high fat-fed pups had significantly higher (P < 0.04) mortality rates than pups of control-fed dams (16.5 and 7.7%, respectively) over the first 3 d of life. Control-fed dams experienced the expected reduction (P < 0.05) in plasma insulin concentrations between the end of pregnancy and early lactation, but high fat-fed dams did not. Thus, physiological mechanisms controlling distribution of metabolic fuels may not be functioning properly in high fat-fed dams. Therefore, consuming a high fat diet reduces a rat's capacity to conceive and ability to maintain her litter during the perinatal period.