Effect of dietary protein and energy on protein synthesis during lactation in rats

A series of experiments was carried out in which effects of dietary protein and energy on protein synthesis during lactation were evaluated. Purified diets were fed to female rats from conception until d 15 of lactation. Protein supplied by wheat gluten, gluten + lysine + threonine or casein + methionine was fed at 20 or 25% in the diet. Protein synthesis in mammary gland and liver was measured with a large dose of L-[4-3H]phenylalanine. As lactation proceeded, protein absolute synthesis rates (ASRs) in casein-fed dams increased from 1056 to 2246 mg/d in mammary gland but remained unchanged in liver. In contrast, ASRs in wheat gluten-fed dams remained unchanged in both tissues. Feeding a protein-free diet or starving dams for 3 d reduced ASR in mammary gland 59 and 72%, respectively, when measured on d 15 of lactation. The corresponding reductions in liver ASR were 41 and 46%. A 20% restriction of dietary energy at a constant protein intake reduced protein synthesis in mammary glands 34, 55 and 28% in dams fed gluten, gluten + lysine + threonine or casein, respectively. In summary, protein synthesis during lactation was reduced less in liver than in mammary gland in response to dietary restriction of protein or energy.     

Response of rat mammary gland transferrin receptors to maternal dietary iron during pregnancy and lactation

Mammalian milk iron (MFe) concentration decreases during lactation. In human attempts to increase MFe through supplementing the mother with iron during lactation have failed and no correlation between maternal iron status or intake and MFe has been determined, suggesting a regulatory mechanism. In contrast MFe in lactating rats can be affected by very high or low amounts of ingested iron. We previously described a transferrin receptor (TfR) mechanism that controls iron entry into rat mammary tissue. In this study lactating rats were used to determine effects of varying dietary iron during gestation and lactation on mammary TfR and MFe. Dams fed low-iron diets had a small increase in TfR, lower hematological indices (p less than 0.005), and lower MFe (p less than 0.005) than did controls or dams fed high iron. Dams fed the high-iron diet had a significant increase in TfR without a concomitant increase in MFe. There was no correlation between MFe and TfR. These findings suggest that control of MFe lies after iron entry into mammary tissue.     

The effects of a dietary zinc supplement during lactation on longitudinal changes in maternal zinc status and milk zinc concentrations

Dietary zinc intakes, selected biochemical indices of zinc status, and milk zinc concentrations were determined at monthly intervals throughout lactation for 53 middle-income lactating women, 14 of whom received a daily supplement of 15 mg zinc. Overall mean dietary zinc intake for the non-supplemented group (NZS) was 10.7 +/- 4.1 mg/day (mean +/- SD). The mean dietary zinc intake of the zinc supplemented group (ZS) was 12.2 +/- 3.5 mg/day, with an additional 12.8 +/- 1.5 mg/day from the supplement. For the NZS group, the highest mean plasma zinc concentration of 79 +/- 10 mu/dl, which occurred at month 4, was significantly less than the mean for non-lactating control women (86 +/- 10 micrograms/dl). ZS plasma zinc levels had a pattern similar to that of the NZS group for months 1-7. The rate of decline in milk zinc during lactation was significantly less for the ZS group compared to that of the NZS group (p = 0.02). It is concluded that milk zinc concentrations are influenced by maternal zinc intake within a physiological range and that the effects of low maternal intakes are most apparent with prolonged lactation.     

Iron status of suckling rats as influenced by maternal diet during gestation and lactation

1. Two experiments are reported. In Expt 1, pregnant Sprague-Dawley rats (200-220 g) were given purified diets containing 35, 75, 150 or 300 mg Fe/kg throughout gestation and lactation. In Expt 2, the levels of Fe given were 250 and 300 mg/kg diet. 2. Litters were standardized at birth to contain seven pups. On day 20 of lactation blood, milk, spleen and liver were collected for Fe analysis. 3. A dietary Fe concentration of 35 mg/kg maintained maximum weight gain, food intake, liver and spleen weight, haemoglobin concentration and packed cell volume in the growing maternal rat through 20 d of lactation. Dam liver and spleen Fe concentrations were maximized between 75 and 250 mg Fe/kg diet. 4. Pups (20-d-old) nursed by dams given 35 mg Fe/kg tended to have lower body and organ weights compared to other groups. Liver and spleen Fe concentrations increased with increasing maternal dietary Fe and were significantly increased between 150 and 250 mg Fe/kg.     

The quantitative effects of maternal dietary energy intake on pregnancy and lactation in rural Gambian women

The quantitative relationships between dietary energy intake and weight gain in pregnancy, birthweight and lactation performance during the first three months of infancy have been studied in such a way as to take account of major differences in the patterns of heavy manual labour at different times of the year in a subsistence farming community. Maternal weight gain and the accumulation of subcutaneous fat were significantly lower when the last trimester of pregnancy fell during the time of heaviest farm work and lowest energy intakes. The birth-weight of babies was also significantly correlated with differences in energy intake throughout the year. During early lactation breast milk yields were significantly related to concomitant alterations in the subcutaneous fat stores. Evidence has been produced which suggests that in undernourished nursing women there could be a competition for dietary energy between the repleting maternal subcutaneous fat organs and the mammary glands at the expense of milk production.     

Intrauterine device and maternal copper metabolism during lactation

The effects of intrauterine device (IUD) on maternal copper (Cu) metabolism during breastfeeding was studied in 95 volunteer mothers who chose to use non-hormonal contraceptive methods. They were divided into two groups that were inserted with the IUD-Cu 380A (n = 33), IUD-Cu 200B (n = 29), and a third group that did not use any IUDs served as control (n = 33). Endometrial biopsies, blood, and milk samples were collected before (at 10 weeks postpartum) and 6 weeks after insertion of device for the determination of metabolites associated with copper metabolism, namely, serum ceruloplasmin, and copper concentrations in breast milk and endometrium. Endometrial copper concentration increased in women using IUDs, but was statistically significant (p = 0.001) only in the IUD-Cu 380A group. The increase in endometrial copper concentration did not affect serum ceruloplasmin or milk copper concentrations.     

Fructose and sucrose feeding during pregnancy and lactation in rats changes maternal and pup fuel metabolism

We examined the effects of feeding a fructose, sucrose or reference diet during gestation and lactation on blood substrate levels and insulin sensitivity in rat adipose tissue. Female rats were fed either 50% fructose or 50% sucrose purified diets or a nonpurified diet ad libitum during gestation and lactation. Fasting blood samples were taken on d 10 of gestation and one oral glucose tolerance test was conducted on d 19 of gestation, with a second test performed on the day of weaning. All dams were killed 2 d after weaning. During gestation, fructose feeding induced hyperglycemia and hypertriglyceridemia in early pregnancy (d 10) relative to sucrose-fed rats, and hypotriglyceridemia in late pregnancy (d 19) as compared with the group fed the reference diet. Compared with the reference group, sucrose feeding also caused hypotriglyceridemia during late pregnancy. Pups delivered to fructose-fed dams were hyperglycemic at birth. In comparison with the reference group, fructose-fed dams were hypoglycemic, whereas sucrose-fed dams were hypertriglyceridemic at weaning. There was no difference in each of the two oral glucose tolerance test responses between the three groups after adjusting for the baseline difference in glucose levels. However, lipid synthesis in isolated fat cells in response to insulin stimulation was significantly lower in fructose-fed and sucrose-fed rats relative to the reference group.     

Maternal dietary restriction during pregnancy and lactation: effect on digestive organ development in suckling rats

To examine the relative effects of maternal malnutrition during pregnancy and lactation on development of the pancreas and small intestine in suckling pups, rats were restricted to 50% of control (C) intake beginning at day 5 of pregnancy. Immediately after birth, some litters were exchanged such that some C dams were suckling pups born to 50%-restricted dams (C/50) and vice versa (50/C). Other litters were allowed to stay with their own mothers, which received a control or restricted diet as during pregnancy (C/C and 50/50). Pups nurtured by restricted dams had reduced body weights, intestinal lengths, hepatic and pancreatic weights, and specific activities of pancreatic lipase and small intestinal brush border sucrase and maltase. Small intestinal lactase levels were higher in the groups of pups from mothers restricted during lactation. In nearly all cases, the 50/C group was the most severely affected while the C/50 group was intermediate between the C/C and 50/50 groups.     

Alterations in immune function in rats caused by dietary lipotrope deficiency: effect of age

Weanling male Sprague-Dawley rats were maintained on a control (C), folacin-deficient (F) or marginal methionine-choline diet (M/C) for 3 weeks, 3 months or 12 months. The immunocompetence of the animals was determined by in vivo (response to infection with salmonella typhimurium) and in vitro (lymphocyte transformation assay) methods. It was found that young animals were most sensitive to dietary lipotrope deficiency, and the in vivo response to bacterial infection did not always correlate with in vitro assessment of immune function. Histopathologic examination of spleens from S. typhimurium-infected rats maintained for 3 weeks on the experimental diets showed an overall decreased cellularity especially in the follicular areas, compared to controls. No differences were seen in the spleens of infected animals at later time points. A short-term (3-week) lipotrope deficiency resulted in a depressed lymphocyte transformation response to concanavalin A (Con A) in the spleen, thymus and lymph nodes; to phytohemagglutinin A (PHA) in the spleen and lymph nodes only. After 3 months on the F or M/C diets, a depressed Con A-induced transformation response was still seen in the spleen, but the normal aging-induced immunosuppression resulted in a low response in all animals, with few significant differences existing among groups.     

Biotin concentrations in maternal plasma and milk during prolonged lactation

We followed a group of exclusively breast feeding mothers for 12 months after delivery. They numbered 200 at delivery, 140 at 4 months of lactation, 116 at 6, 36 at 9 and 7 at 12 months. The milk concentration of biotin was very low at delivery and subsequently the (geometric) mean value remained at around 4.5 micrograms/l. The mean plasma value was 250 ng/l at delivery and stable (around 330 ng/l) throughout the lactation. There were large intra- and interindividual variations in the concentrations in both milk (from 0 to 27 micrograms/l) and plasma (from 142 to 1090 ng/l). The variations in the milk concentrations result in a similar variation in the biotin intake of the exclusively breast-fed infants. The current recommendations for biotin intake were not met by any of those infants but no manifestations of biotin deficiency were recorded.     

Ethanol intake during lactation impairs milk production in rats and affects growth and metabolism of suckling pups.

From parturition, lactating Wistar rats were given 20% alcohol in drinking water and fed a solid diet ad lib (group AL). Pair-fed (PF) and control (C) rats were fed solid diet and given water ad lib (C). All animals were sacrificed on the 12th day of lactation. Ethanol treatment decreased food intake and milk production in lactating rats to a greater level than in PF rats, and a greater reduction in body weight of the AL pups was noted. Brain weight, protein concentration, and DNA content were also lower in pups of AL dams than of PF dams, whereas liver glycogen concentration was higher in the former. Pups from AL dams had higher circulating levels of beta-OH-butyrate, triglyceride, and free fatty acids than those from either C or PF dams. Plasma glucose concentration was lower in both PF and AL than in C pups, whereas the AL group had lower plasma protein concentration than any of the other groups. We conclude that maternal alcohol intake during lactation greatly impairs milk production, and although the known increase of lipid content in milk in rats studied under similar conditions allows an enhanced lipidic components in the pups, this adaptation does not allow normal growth and brain development.     

Marginal zinc deficiency affects maternal brain microtubule assembly in rats

The possible physiological role of Zn in tubulin polymerization was studied. Tubulin assembly in vitro was characterized in brain supernatants from rats fed a marginally Zn-deficient diet (10 micrograms Zn/g) during pregnancy and lactation. The initial rate of tubulin polymerization was significantly lower (27%) in brain supernatants from the marginally Zn-deficient animals than from controls. This was associated with a lower Zn concentration in the brain supernatants from the marginally deficient rats. Total protein and tubulin concentrations were the same in the supernatants from both groups. These data show that Zn is necessary for normal tubulin assembly and indicate that one biochemical defect underlying brain alterations in Zn deficiency could be abnormal microtubule function.     

孕期和哺乳期双酚A暴露对母鼠体内糖代谢及瘦素水平的影响

目的研究孕期和哺乳期暴露双酚A(bispheno1 A,BPA)对母鼠体内糖代谢及血清瘦素水平的影响。方法将18只妊娠的健康清洁级SD雌性大鼠随机分为3组,分别为对照组(含1%乙醇溶液)和低剂量(1 mg/L)、高剂量(10mg/L)BPA染毒组,每组6只。从妊娠第6天至哺乳期[哺乳(lactation day,LD)21 d]结束,采用自由饮水方式进行染毒。测定母鼠空腹时血糖及血清胰岛素、瘦素水平,并计算胰岛素抵抗指数。结果与对照组比较,断乳后各剂量BPA染毒组母鼠空腹时血糖、胰岛素和瘦素水平及胰岛素抵抗指数均显著增高,差异有统计学意义(P<0.05,P<0.01);与低剂量BPA染毒组比较,高剂量BPA染毒组母鼠血清胰岛素水平和胰岛素抵抗指数均明显增高,差异有统计学意义(P<0.05)。且随着BPA染毒浓度的升高,母鼠空腹时血糖及血清胰岛素、瘦素水平和胰岛素抵抗指数均呈上升趋势。结论孕期和哺乳期暴露BPA可引起母鼠胰岛素抵抗,这可能与血清瘦素水平升高有关。     

A maternal high-fat/high-caloric diet delays reflex ontogeny during lactation but enhances locomotor performance during late adolescence in rats

Objective: The main goal of the present study was to investigate the effects of two maternal high-fat diets with different energy densities on the somatic growth, reflex ontogeny, and locomotor activity of offspring.

Methods: Twenty-nine female Wistar rats (220–250?g) were mated and grouped into three different dietary conditions: control (n?=?11, AIN-93G diet, 3.6?kcal/g), high-fat/high-caloric (HH, n?=?9, 51% of the calories from fat, 4.62?kcal/g), and high-fat/isocaloric (HI, n?=?9, 51% of the calories from fat, 3.64?kcal/g). The fat source was mainly lard. The dietary groups were maintained during gestation and lactation. From postnatal day 1 (PND1) until weaning, the somatic growth, maturation of physical features, and reflex ontogeny of the male pups were evaluated. The locomotor activity was evaluated in an open field at PND8, PND14, PND17, PND21, PND30, PND45, and PND60.

Results: HH dams had a lower food intake but no difference in caloric intake or body weight gain. The HH pups had higher body weights, greater tail and body lengths, and an increased axis of the head at weaning. The prediction of ear unfolding, delayed palmar grasp, and cliff avoidance maturation were also observed in the HH offspring. At PND60, the HH pups showed an increased average speed as well as an average potency and kinetic energy in the open field.

Conclusion: A high-fat/high-caloric maternal diet increases somatic growth, predicts the maturation of physical features, and delays reflex ontogeny during lactation, and it enhances motor performance during late adolescence. A maternal HI diet does not elicit the same influences on offspring development compared with the HH diet.     

Changes in the endorphin and serotonin content of rat immune cells during adulthood following maternal exposure to ethanol during pregnancy and lactation.

Lactating and lactating/pregnant rat dams consumed either 3% (vol/vol) ethanol (as the sole source of fluid) between the 1st and 21st days after delivery or 15% (vol/vol) ethanol for 24h on the 3rd day after delivery. Offspring of ethanol-consuming dams were compared with offspring of untreated control dams. In other groups, offspring of mothers given 3% ethanol during pregnancy were also compared to untreated controls. When the offspring were 2 months of age, endorphin and serotonin contents of immune cells (lymphocytes, granulocytes and monocytes, mast cells of the peritoneal fluid, and lymphocytes of the thymus) were determined by hormone-specific antibodies and flow cytometric as well as confocal microscopic analysis. In rats exposed to ethanol through breast-feeding, endorphin content significantly decreased in thymic cells independent of the alcohol concentration (and duration) during treatment. Each type of peritoneal cell contained significantly more serotonin after 3% alcohol treatment. For the prenatally exposed offspring, serotonin content significantly decreased for both ethanol treatment conditions during pregnancy. Remarkably, one day of exposure to 15% ethanol on the third day of pregnancy was sufficient to induce this enduring change in serotonin content of immune cells of offspring. Considering that endorphin and serotonin are important immunomodulators, these alcohol-induced changes could produce enduring influences on immune function.     

High dietary folate supplementation affects gestational development and dietary protein utilization in rats.

There is new evidence that good folate status may play a critical role in the prevention of neural tube defects and in the maintenance of adequate homocysteine levels, an amino acid recently identified as a risk factor for cardiovascular disease. This has led to different folate recommendations, all of them much higher than the present dietary recommendations. Folic acid is a water-soluble vitamin with a low potential toxicity. However, the possible consequences of long-term, high folate intakes are unknown. Therefore, the present study was undertaken to determine the effects of long-term, high dietary folate supplementation on gestational and nutritional markers in pregnant and virgin rats. Four groups of Wistar rats were classified on the basis of physiological status (virgin or pregnant) and the experimental diets administered (folic acid supplemented, 40 mg/kg diet; or control diet, 2 mg folic acid/kg diet). Rats were fed their respective diets for 3 wk. Two critical periods were used for metabolic balance studies (experimental d 1-5 and 17-21), which involved the determination of fat and protein digestibilities as well as metabolic protein utilization (MPU) and net protein utilization (NPU). Gestational development (number of live fetuses) was adequate in both diet groups regardless of folate supplementation. However, body weight and vertex-coccyx length in fetuses from supplemented dams were less than (P < 0.0001) in fetuses of control dams. Fat and nitrogen digestibilities were not affected by supplementation, but MPU and NPU coefficients were significantly lower (P < 0.05) in the folic acid-supplemented groups, irrespective of physiological status, compared to control rats. These new findings of macro-micronutrient interactions caused by high folate supplementation are discussed on the basis that the vitamin may act as a xenobiotic more than as a nutrient.     

Assessment of dietary vitamin D requirements during pregnancy and lactation

Concerns about vitamin D have resurfaced in medical and scientific literature because the prevalence of vitamin D deficiency in the United States, particularly among darkly pigmented persons, has increased. The primary goals of this review were to discuss past and current literature and to reassess the dietary reference intake for vitamin D in adults, with particular focus on women during pregnancy and lactation. The appropriate dose of vitamin D during pregnancy and lactation is unknown, although it appears to be greater than the current dietary reference intake of 200-400 IU/d (5-10 microg/d). Doses of < or =10 000 IU vitamin D/d (250 microg/d) for up to 5 mo do not elevate circulating 25-hydroxyvitamin D to concentrations > 90 ng/mL, whereas doses < 1000 IU/d appear, in many cases, to be inadequate for maintaining normal circulating 25-hydroxyvitamin D concentrations of between 15 and 80 ng/mL. Vitamin D plays no etiologic role in cardiac valvular disease, such as that observed in Williams syndrome, and, as such, animal models involving vitamin D intoxication that show an effect on cardiac disease are flawed and offer no insight into normal human physiology. Higher doses of vitamin D are necessary for a large segment of Americans to achieve concentrations equivalent to those in persons who live and work in sun-rich environments. Further studies are necessary to determine optimal vitamin D intakes for pregnant and lactating women as a function of latitude and race.