A high dietary lipid intake during pregnancy and lactation enhances mammary gland lipid uptake and lipoprotein lipase activity in rats.

Rats fed a diet with high fat concentration produce larger amounts of milk with a higher lipid concentration than rats fed a lower fat diet. This investigation was designed to study the relationship between dietary fat intake, mammary gland lipid uptake and lipogenesis in rat dams fed, during pregnancy and lactation, one of two purified diets, with equal energy density, containing 2.5 (LL) or 20 g fat/100 g diet (HL). Milk lipid concentration and fatty acid composition were determined at d 14 of lactation. Mammary gland lipogenesis, lipoprotein lipase (LPL) activity and the uptake of [1-(14)C]triolein by the mammary gland and its transfer to the pups was measured. The intestinal absorption of oral (14)C-lipid, (14)CO(2) production and the amount of (14)C-lipid transferred to the pups (milk clot + pups carcass) were significantly higher in the HL group than in the LL group (P < 0.05). Mammary gland lipogenesis was 75% lower and LPL activity was 30% higher in the HL group (P < 0.05). Medium-chain fatty acids (C6-C14) excretion was 46% lower and that of long-chain fatty acids was 142% (P < 0.001) higher in the HL group than in the LL group. The higher milk lipid excretion in the rats fed a high-fat diet resulted from a larger uptake of dietary lipid by the mammary gland, indicated by a larger transfer of (14)C-lipid to the pups and by a higher LPL activity in the mammary gland.     

Dietary conjugated linoleic acids lower the triacylglycerol concentration in the milk of lactating rats and impair the growth and increase the mortality of their suckling pups

Recent studies showed that conjugated linoleic acids (CLA) lower triacylglycerol concentrations in the milk of lactating animals. This study was performed to determine the reasons for this phenomenon; we also investigated whether there is a relation between altered lipid metabolism in the liver and the reduction in milk triacylglycerols in rats fed CLA. Two groups of female rats were fed diets containing 0 [sunflower oil (SFO) group] or 14.7 g/kg diet of a CLA mixture (CLA group) at the expense of sunflower oil during growth, pregnancy, and lactation. CLA-fed rats had 49 and 80% lower mRNA concentration and activity of fatty acid synthase, respectively, a 51% lower mRNA concentration of lipoprotein lipase (LPL) in their mammary glands at d 17 of lactation, and a 46% lower milk fat content than SFO rats (P < 0.05). Although CLA rats had lower concentrations of triacylglycerols in the liver than SFO rats (20.8 +/- 2.6 vs. 62.6 +/- 27.7 micromol/g, P < 0.05), concentrations of triglycerides in plasma, which are the substrates of LPL, did not differ between the groups. Moreover, the number of pups per litter, litter weights, and pup weights at d 17 of lactation were 41, 35, and 22% lower, respectively, in the CLA group than in the SFO group. In conclusion, the present study suggests that dietary CLA reduces triacylglycerol concentrations in the milk via reduced de novo fatty acid synthesis in the mammary gland and an impaired uptake of fatty acids from lipoproteins into the mammary gland. This might be the reason for reduced growth rates and an increased mortality of suckling pups.     

Dietary vitamin A has both chronic and acute effects on vitamin A indices in lactating rats and their offspring

To further investigate the effect of dietary vitamin A (VA) intake on milk VA concentrations and pup VA status, female rats were fed 2 concentrations of VA [0 (n = 9) or 50 micromol/kg diet (n = 10)] during pregnancy and lactation. Plasma retinol concentrations were significantly higher (30-40%) during lactation than before pregnancy or after weaning but were not influenced by dietary VA. In rats fed VA, VA concentrations during lactation were significantly higher in milk (1.5-3 times), mammary tissue (>100%), liver (4 times), pup plasma (20-40%), and pup liver (1.1-6.7 times). In Expt. 2, when VA intake was switched on d 7 of lactation from 0 to 50 micromol/kg, milk VA concentrations (2.24 +/- 0.42 micromol/L; mean +/- SD, n = 6) increased significantly (1.7 times) by d 9 to the same level as in rats administered 50 micromol/kg (6.04 +/- 0.60 micromol/L; n = 6). When VA was removed from the diet on d 7, concentrations declined significantly (by 50%) and by d 11 were the same as those in rats given 0 micromol/kg. We conclude that the rapid effect of changes in dietary VA intake are attributable to changes in the delivery of chylomicron VA to mammary tissue and milk.     

Wheat gluten during pregnancy and lactation: effects on mammary gland development and pup viability

Diets containing 13% protein supplied by wheat gluten (WG), wheat gluten + lysine + threonine (WGLT), or casein + methionine (CM) were fed to pregnant rats from conception through day 15 of lactation. A crossover design was used with combinations of WG, WGLT, and CM during pregnancy and lactation. Out of six dams fed WG during both pregnancy and lactation and nursing a total of 48 pups on day 1 of lactation, only two pups were still alive on day 15 of lactation. In contrast, CM dams still were nursing 47 pups at this time. Differences in the weight and composition of mammary tissue were directionally similar to and consistent with pup viability. The data obtained confirm the importance of protein quality in the lactation diet and also demonstrate that deficits in mammary gland development occurring during pregnancy may not necessarily be overcome by a nutritionally adequate diet consumed during lactation.     

Vitamin A intake affects the contribution of chylomicrons vs. retinol-binding protein to milk vitamin A in lactating rats

To investigate the influence of vitamin A intake on the contribution of chylomicrons vs. holo retinol-binding protein to milk vitamin A, female rats were fed diets containing either 10 (n = 6) or 50 micromol vitamin A/kg body (n = 4) during pregnancy and through d 13 of lactation. [3H]Vitamin A was incorporated into each diet beginning on d 6 of lactation. Vitamin A concentrations on d 13 were significantly higher in dam liver (x 3), pup liver (x 2.6), milk (x 2.5) and mammary tissue (x 1.3) in rats consuming the higher level of vitamin A. In both groups, vitamin A specific activities in plasma and milk reached apparent plateaus by 2.33 d after addition of [3H]vitamin A to the diets. Vitamin A specific activity in milk was higher than in plasma at all times in both groups. The estimated minimum contribution of chylomicrons to milk vitamin A was 32 +/- 3% in rats fed the lower level of vitamin A vs. 52 +/- 10% at the higher level (P = 0.014). We concluded that dietary vitamin A, like triglycerides, may be directed to mammary tissue during lactation for preferential secretion into milk; thus, increasing vitamin A intakes will increase the contribution of dietary vitamin A to milk. In contrast to milk, mammary tissue vitamin A turns over very slowly.     

Effects of feeding fat during pregnancy and lactation on growth performance, milk composition and very low density lipoprotein composition in ratstc "density lipoprotein composition in rats"

The effects of dietary fat during pregnancy and lactation on growth performance of pups, milk composition and very low density lipoprotein composition in rats were studied. A total of 33 dams were used in this study and each litter was adjusted to 8 pups per dam. The dams were fed on high fat (150 g fat/kg diet, HF), medium fat (75 g fat/kg of diet, MF) and low fat (2.5 g fat/kg diet, LF) diets. The body weights of dams increased during pregnancy and decreased after pregnancy. The HF pups had a higher body weight and higher weight gain than those of LF pups. The amount of feed intake of HF dams was significantly higher than LF and MF dams. The HF dams had significantly higher milk fat and water concentrations than LF dams. The milk protein was not significantly different among the treatment groups. All dams showed hypertriacylglycerolaemia in their very low density lipoprotein (VLDL) in late pregnancy. The VLDL-protein concentrations increased during the first week after parturition. The HF dams showed a greater response to the dietary fat than that of LF and MF dams. The findings suggest that addition of fat in the diet during pregnancy and lactation may improve the milk quality through modifying the composition of VLDL contents, leading to better growth of pups.     

Marginal maternal Zn intake in rats alters mammary gland Cu transporter levels and milk Cu concentration and affects neonatal Cu metabolism

Marginal zinc intake is common and leaves women particularly vulnerable to Zn deficiency due to increased demand for Zn as a consequence of reproduction. Zn deficiency during pregnancy and lactation has been associated with secondary affects on copper metabolism in the offspring; however, the underlying mechanisms are unknown. The effects of marginal maternal Zn intake on maternal and neonatal Cu metabolism were determined in rats. Plasma, milk and tissue Cu and Zn concentrations and plasma and milk ceruloplasmin (Cp) activity were measured in dams fed a control (CON, 25 mg Zn/kg diet) or a marginal Zn diet (ZD, 10 mg Zn/kg diet) and their suckling pups. There was no effect on maternal tissue Cu or Zn or milk Zn concentration; however, plasma Cp activity was higher in dams fed ZD, suggesting that Cp activity may be a useful marker for identifying marginal Zn status. Rats fed ZD had high mammary gland Ctr1, Atp7A and Atp7B levels, milk Cp activity and Cu concentration. Immunostaining and differential centrifugation indicated that ZD also altered Ctr1 and Atp7A localization in the mammary gland. Pups from dams fed ZD had higher small intestine Cu and lower plasma Cu than CON pups. These results suggest that marginal maternal Zn intake during pregnancy and lactation increase mammary gland Cu transporter levels and alter their localization, resulting in high milk Cu levels, possibly in response to transiently elevated plasma Cu levels. The combination of high milk Cu concentration and immature neonatal Cu transport exposes the suckling neonate to excess Cu; however, whether this occurs in humans is not yet known.     

Evidence for increased selenium requirement for the rat during pregnancy and lactation

Adequacy of the National Research Council (NRC) selenium (Se) requirement for growth (0.1 ppm Se) was assessed in reproducing Sprague-Dawley rats. Either a casein-based diet with no added Se or the same diet supplemented with selenite to contain 0.05, 0.1, or 0.2 ppm Se was fed during pregnancy and lactation and to nonreproducing controls. Only 0.05 ppm Se was necessary to maintain maximal red blood cell (RBC) and liver Se concentrations and glutathione peroxidase (GSH-Px) activities in controls, whereas 0.2 ppm Se was necessary to maintain comparable RBC Se during pregnancy and tissue Se and GSH-Px activities during lactation. On d 2 of lactation, no differences in pup tissue Se or GSH-Px activities could consistently be related to maternal Se intake. By d 18 of lactation, however, Se status of nursing pups reflected maternal Se intake. Pups of dams fed 0.2 ppm Se had tissue Se and GSH-PX activities significantly greater than those of all other pups. Milk Se content correlated significantly with maternal Se intake and plasma Se and with pup tissue Se and GSH-Px activities. These results indicate that during reproduction 0.1 ppm Se is not adequate to maintain maternal tissue Se or GSH-Px activities comparable to those of normal controls; 0.2 ppm dietary Se is more appropriate, resulting in maternal GSH-PX activities similar to those of controls fed 0.1 ppm Se and milk Se concentrations that result in greater pup tissue GSH-Px activities.     

Increased rat mammary tissue vitamin A associated with increased vitamin A intake during lactation is maintained after lactation

Although increases in dietary vitamin A increase milk vitamin A, little is known about effects of vitamin A intake on mammary tissue vitamin A levels during and after the reproductive cycle. First, we measured vitamin A concentrations in milk, mammary tissue and liver of lactating rats fed 0, 4, or 50 micromol of vitamin A/kg diet during pregnancy and through d 12 of lactation. Liver vitamin A concentration was significantly affected by diet in lactating females and pups 12 d after parturition. Milk vitamin A concentrations were significantly higher (7.1 +/- 2.2 micromol/L, n = 8) in dams fed 50 micromol/kg than in those fed 0 or 4 micromol/kg (1.9 +/- 0.3, n = 5 and 2.9 +/- 0.7 micromol/L, n = 7; P < 0.001), as were mammary tissue vitamin A concentrations (5.1 +/- 1.1 versus 2.2 +/- 0.4 and 2.4 +/- 0.6 nmol/g; P < 0.001). Next, we maintained female rats on 50 or 10 micromol vitamin A/kg diet during pregnancy and lactation and then on 4 micromol/kg diet after pups were weaned on d 21. On d 21, mammary tissue vitamin A concentrations were 3.14 +/- 0.75 versus 1.52 +/- 0.21 nmol/g in dams fed 50 versus 10 micromol/kg (n = 4/group; P < 0.001). Mammary tissue vitamin A concentrations were not significantly affected by time from 7 to 49 d after lactation and averaged 8.5 +/- 0.4 and 4.9 +/- 0.8 nmol/g on d 49 in dams fed 50 versus 10 micromol/kg (n = 4; P < 0.001). We conclude that diet-induced differences in rat mammary tissue vitamin A developed during pregnancy and lactation are maintained for > or =7 wk after lactation.     

Oxidized fat reduces milk triacylglycerol concentrations by inhibiting gene expression of lipoprotein lipase and fatty acid transporters in the mammary gland of rats

Feeding oxidized fats to lactating rats causes a strong reduction of triacylglycerol concentration in the milk. The reason for this, however, has not yet been elucidated. Pregnant Sprague-Dawley rats were assigned to 2 groups of 11 rats each and fed diets containing either fresh fat (FF group) or an oxidized fat (OF group) from d 1 to d 20 of lactation. Concentrations of triacylglycerols and long-chain fatty acids in the milk and weight gain of suckling pups were lower in the OF group than in the FF group (P < 0.05). Concentrations of medium-chain fatty acids in the milk and messenger RNA (mRNA) abundance of lipogenic enzymes in the mammary gland did not differ between the 2 groups of rats. However, the OF group had a lower concentration of triacylglycerols and nonesterified fatty acids (NEFA) in plasma and lower mRNA concentrations of lipoprotein lipase and fatty acid transporters in the mammary gland than the FF group (P < 0.05). Moreover, the OF group had higher mRNA concentrations of hepatic lipase, fatty acid transporters, and several genes involved in fatty acid oxidation in the liver than the FF group (P < 0.05). The present findings suggest that a dietary oxidized fat lowers the concentration of triacylglycerols in the milk by a reduced uptake of fatty acids from triacylglycerol rich-lipoproteins and NEFA into the mammary gland. The study, moreover, indicates that an oxidized fat impairs normal metabolic adaptations during lactation, which promote the utilization of metabolic substrates by the mammary gland for the synthesis of milk.     

Zinc metabolism in pregnant and lactating rats and the effect of varying iron: Zn in the diet

Pregnant rats were given control (46 mg iron/kg, 61 mg zinc/kg), low-Zn (6.9 mg Zn/kg) or low-Zn plus Fe (168 mg Fe/kg) diets from day 1 of pregnancy. The animals were allowed to give birth and parturition times recorded. Exactly 24 h after the end of parturition the pups were killed and analysed for water, fat, protein, Fe and Zn contents and the mothers' haemoglobin (Hb) and packed cell volume (PCV) were measured. There were no differences in weight gain or food intakes throughout pregnancy. Parturition times were similar (mean time 123 (SE 15) min) and there were no differences in the number of pups born. Protein, water and fat contents of the pups were similar but the low-Zn Fe-supplemented group had higher pup Fe than the low-Zn unsupplemented group, and the control group had higher pup Zn than both the low-Zn groups. The low-Zn groups had a greater incidence of haemorrhaged or deformed pups, or both, than the controls. Pregnant rats were given diets of adequate Zn level (40 mg/kg) but with varying Fe:Zn (0.8, 1.7, 2.9, 3.7). Zn retention from the diet was measured using 65Zn as an extrinsic label on days 3, 10 and 17 of pregnancy with a whole-body gamma-counter. A group of non-pregnant rats was also included as controls. The 65Zn content of mothers and pups was measured 24-48 h after birth and at 14, 21 and 24 d of age. In all groups Zn retention was highest from the first meal, fell in the second meal and then rose in the third meal of the pregnant but not the non-pregnant rats. There were no differences between the groups given diets of varying Fe:Zn level. Approximately 25% of the 65Zn was transferred from the mothers to the pups by the time they were 48 h old, and a further 17% during the first 14 d of lactation. The pup 65Zn content did not significantly increase after the first 20 d of lactation but the maternal 65Zn level continued to fall gradually.     

Some metabolic effects on lactating rats of a low-energy diet restricted in good-quality protein

Adult female Sprague-Dawley rats were fed ad libitum during pregnancy and lactation a control diet (CD; 16.1 kJ/g) or a low-energy diet with wheat gluten as the main protein source (LED; 13.3 kJ/g). Body weight, food intake, resting energy expenditure, respiratory quotient and substrate use by the mammary gland were measured. After the animals had been killed, the parametrial and retroperitoneal fat pads were weighed. The mean food intake (g) of the two groups of rats was similar, resulting in a lower energy intake by the LED rats, significantly different during the last 2 weeks of lactation. The mean body weight of both dams and pups in the LED group was lower, starting at day 9 of lactation. The resting energy expenditure increased gradually during lactation in the control group, whereas this increase was not seen in rats of the LED group in the last week of lactation. Rats that had fasted overnight had a respiratory quotient of 0.7 or less, whereas for rats that had been fed, the mean respiratory quotient was over 1.0. Under both conditions, rats showed ketonuria. The arteriovenous difference in 3-hydroxybutyrate level was higher and those for glucose, lactate and triacylglycerol were lower across the mammary glands of LED rats. The parametrial fat depot weighed less in LED rats. Reducing the increase in resting energy expenditure and using ketone bodies to a greater extent as fuels may represent important mechanisms in the LED dams to cover the energy cost of milk production.     

Vitamin A during lactation: relationship of maternal diet to milk vitamin A content and to the vitamin A status of lactating rats and their pups

We have investigated the effects of maternal vitamin A intake during pregnancy and lactation or during lactation alone on the concentration of vitamin A in rat's milk and on vitamin A levels in plasma and liver of dams and their pups. Groups of Sprague-Dawley rats were fed diets having either a high vitamin A content [15 retinol equivalents (R.E.)/g diet] or a low vitamin A content (0.6 R.E./g) for 42 d, including 7-8 d prior to pregnancy, pregnancy, and for 14 d of lactation. The concentration of vitamin A in milk on d 14 of lactation was significantly greater on the high vitamin A diets [114 +/- 16 micrograms/dl (mean +/- SEM; n = 8) versus 52 +/- 7.3 micrograms/dl (n = 11), P less than 0.005]. However, milk vitamin A concentration on d 1 of lactation did not vary with maternal vitamin A intake during pregnancy. In a second study in which supplementation with vitamin A (30 R.E./g diet) was begun on d 1 postpartum, the milk vitamin A content increased progressively with duration of lactation. Maternal plasma vitamin A concentrations did not differ between rats fed the higher or lower vitamin A diets. However, liver vitamin A concentrations both of dams and of their 14-d-old pups were significantly higher when dams were fed the higher vitamin A diets during pregnancy and/or lactation. The results of these studies indicate that the transfer of vitamin A from mother to offspring by milk and the vitamin A status of dams and their suckling neonates is influenced by maternal vitamin A intake during lactation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Iron transporters in rat mammary gland: effects of different stages of lactation and maternal iron status

BACKGROUND: Mechanisms regulating iron transfer from maternal circulation into milk are yet unknown. Whether intestinal iron transporters, divalent metal transporter 1 (DMT1) and ferroportin 1 (FPN1), are present in the mammary gland and are involved in iron transfer into milk are unknown. OBJECTIVE: The objective was to examine DMT1 and FPN1 in rat mammary gland at different stages of lactation and to evaluate the effects of maternal iron status. DESIGN: Rats were fed either 35 mg Fe (control rats) or 8 mg Fe (low-iron rats) per kg diet for 3 wk and were fed the same diet throughout pregnancy and lactation. Mammary gland DMT1, FPN1, transferrin receptor, and ferritin were examined in control rats on days 1, 5, 10, and 20 of lactation and in low-iron rats on days 10 and 20 of lactation. Tissue and milk iron were measured. RESULTS: Milk iron, DMT1, and FPN1 decreased throughout lactation. Iron status was compromised in low-iron rats, whereas milk iron was maintained. On day 10 of lactation, mammary gland iron and ferritin were lower in the low-iron rats. DMT1, FPN1, and transferrin receptor values were unchanged; however, a smaller-size DMT1 protein was observed in the low-iron rats. On day 20, transferrin receptor increased in the low-iron rats, whereas mammary gland iron, ferritin, DMT1, and FPN1 were unchanged. CONCLUSIONS: The results show that DMT1 and FPN1 concentrations are higher during early lactation and are possibly involved in iron transfer into milk. Mammary gland regulation of DMT and FPN1 during low iron status appears to be different from that in the intestine.     

Maternal zinc deficiency raises plasma prolactin levels in lactating rats

There is an inverse relation between zinc (Zn) intake and plasma prolactin in men and nonpregnant women. Whether a relation exists in lactating women is unknown, despite the potential consequences of perturbations in prolactin regulation on lactation performance. We examined the effects of low Zn intake on prolactin concentration, the prolactin regulatory pathway in the pituitary gland, and lactation performance in lactating rats. Female rats were fed diets containing 7 (zinc deficient; ZD), 10 (marginally zinc deficient; MZD) or 25 mg Zn/kg (control) from 70 d preconception to lactation d 11. Rats were killed, pituitary glands dissected, and tissues and plasma collected and analyzed for prolactin concentration. Pituitary gland pituitary factor 1 (Pit-1), dopamine 2 receptor (D2R), and prolactin receptor mRNA expression were measured in the pituitary gland. Liver, mammary gland, plasma, and milk Zn were measured. Milk intake of the pups was also recorded. Plasma prolactin concentration was higher in rats fed the ZD (125.9 microg/L) diet compared with control rats (21.7 microg/L). Pituitary gland prolactin concentration was higher in rats fed the ZD diet (69.8 mg/g total protein) compared with controls (29.0 mg/g). Plasma Zn concentration was lower in rats fed the MZD and ZD diets, and mammary gland and milk Zn concentrations were lower in rats fed the ZD diet compared with control rats. Rats fed the ZD diet had lower D2R, prolactin receptor, and Pit-1 mRNA levels, whereas rats fed the MZD diet had lower prolactin receptor and Pit-1 mRNA levels compared with control rats. Milk intake was lower in pups of rats fed the MZD and ZD diets. Our results suggest that marginal Zn nutriture may compromise milk production despite increased prolactin levels. In addition, increased circulating prolactin concentration is not due to altered nursing behavior, but may be due to alterations in the prolactin regulatory pathway in the pituitary gland.     

Fatty acids and retinyl esters of rat milk: effects of diet and duration of lactation

This study was initiated to explore the quantitative and qualitative differences in milk total fatty acids and milk retinyl esters when either hydrogenated or nonhydrogenated fat is fed during pregnancy and lactation. Rats were fed diets containing 10% by weight of corn oil or partially hydrogenated corn oil. Milk was collected on d 1, 8 and 14 of lactation and analyzed for protein, total fatty acids, fatty acid pattern, and retinyl ester pattern. Whereas diet produced no quantitative differences in milk protein or total fatty acids, the pattern of milk fatty acids varied significantly. Rats fed corn oil produced milk having more medium-chain saturated fatty acids, less long-chain monoenoic fatty acids, and more polyunsaturated fatty acids compared to those fed hydrogenated corn oil. Rats fed hydrogenated corn oil produced milk fat having 21-26% of the trans fatty acid, elaidic acid. Significant differences were also observed with duration of lactation: medium-chain fatty acids increased three to fourfold between d 1 and 8, where cis-monoenes and polyunsaturated fatty acids declined. The pattern of milk retinyl esters strongly reflected, but was not identical to, that of total milk fat. Comparing d 14 milk from rats fed corn oil with that from rats fed hydrogenated corn oil, medium-chain esters of retinol constituted 24 and 11% of total retinyl esters, whereas saturated long-chain fatty acid esters constituted 52 and 44%, respectively. trans Fatty acid esters of retinol comprised 24% of vitamin A esters in milk of rats fed hydrogenated fat. These data provide evidence that the composition of milk retinyl esters, as well as that of total milk fat, is determined both by the type of fatty acids from diet and from diet-related differences in de novo synthesis of fatty acids within the mammary gland and other tissues.     

Lactoferrin Supplementation during Gestation and Lactation Is Efficient for Boosting Rat Pup Development

Lactoferrin (LF) is an iron-binding protein found at relatively high concentrations in human milk. LF, which is little degraded in the infant intestinal lumen, is known to stimulate the proliferation and differentiation of the small intestine epithelial cells. The present study was designed to evaluate in the rat model the effects of bovine LF (bLF) given to the mothers during gestation and lactation on the growth of the offspring. Female Wistar rats were randomly separated into two groups of animals that received from mating and during gestation and lactation a standard diet including or not including bLF (10 g/kg of diet). The pups’ growth was determined up to postnatal day 17 (PND17), and parameters related to lean and fat mass, intestinal differentiation, intestinal barrier function, bone mineral density, osteoblast activity, and brain development were measured. In addition, metabolites in pup plasma were determined at PND17. bLF was detected in the plasma and milk of the supplemented mothers as well as in the pup plasma. Although the body weight of the pups in the two groups did not differ at birth, the pups recovered from the supplemented mothers displayed an increase body weight from PND12 up to PND17. At PND17 in the bLF group, increased small intestine epithelial cell differentiation was detected, and colon barrier function was reinforced in association with increased expression of genes coding for the tight-junction proteins. Regarding bone physiology, improved bone mineral density was measured in the pups. Lastly, the plasma metabolite analysis revealed mainly higher amino acid concentrations in the LF pups as compared to the control group. Our results support that bLF ingestion by the mother during gestation and lactation can promote pup early life development. The potential interest of supplementing the mothers with bLF in the case of risk of compromised early life development of the offspring in the context of animal and human nutrition is discussed.     

Protein synthesis in mammary acini isolated from lactating rats: effect of maternal diet

Protein synthesis in the rat mammary gland has been studied using acini isolated from mammary tissue by collagenase digestion. When the acini were incubated with radioactively labeled amino acids, both cellular and milk proteins were synthesized and milk proteins were secreted into the incubation medium. Antisera to the lipogenic enzyme, fatty acid synthase, and the milk proteins, alpha-lactalbumin and the caseins, raised in rabbits, were shown to be specific by analyzing immunoprecipitates on sodium dodecyl sulfate--polyacrylamide gels. The rates of synthesis and secretion of each protein by acini prepared from rats during late gestation and at specific stages of lactation reflect their previously observed concentration in the mammary gland or milk of rats at the corresponding stage of gestation or lactation. Rats were treated according to one of the following regimes between d 7 and 14 of lactation: they were fed a control (20% casein) or a low protein (10% casein) diet ad libitum, they were fed the control diet restricted to 25 g/d (40% of the voluntary intake), they were fed the control diet for 5 d and starved for 48 h or they were treated as in 3 and then refed the control diet ad libitum for 24 h. Food restriction and starvation both resulted in lowered rates of synthesis of all proteins examined compared with either the control or refed animals. Starvation also lowered the rates of secretion of the milk proteins. Consumption of the low protein diet caused a specific decrease in both the rates of synthesis and secretion of alpha-lactalbumin compared with the control rats without affecting the synthesis and secretion of the caseins.     

The effects of exercise on milk yield, milk composition, and offspring growth in rats

This study examined effects of exercise training throughout pregnancy and lactation upon selected indicators of lactational performance in Wistar rats. During the 7 wk prior to mating, experimental female rats were gradually trained to swim for 2 h/day, 5 days/wk with a 3% tail weight; they continued swimming until the 19th day of pregnancy. Control animals remained sedentary. Swimming resumed during days 2-14 of lactation. Food intake was greater in exercised rats during the lactation period. Body weights of the two groups were comparable. Mild yield (day 10), energy content (day 15), and protein and fat concentrations did not differ, but milk of exercised rats had a lower lactose concentration. The exercise regimen had no statistically significant effect on litter size or on offspring weight to day 15. This study indicates that moderate-intensity, aerobic exercise does not markedly affect the lactational performance of ad libitum-fed rats.     

Reduced energy intake and moderate exercise reduce mammary tumor incidence in virgin female BALB/c mice treated with 7,12-dimethylbenz(a)anthracene

This study evaluated the concurrent effects of diet (standard AIN-76A, restricted AIN-76A and high-fat diet) and moderate rotating-drum treadmill exercise on the incidence of 7,12-dimethylbenz(a)anthracene-induced mammary carcinomas in virgin female BALB/cMed mice free of murine mammary tumor virus. Exercise significantly reduced food consumption in the groups fed the standard diet and high fat diet. Although food consumption varied widely, final body weight was similar in all groups. Exercise had no effect on mammary tumor incidence in the standard diet-fed groups (without exercise, 47%; with exercise, 45%); however, exercise reduced mammary tumor incidence in the other groups as follows: restricted diet/no exercise, 28%; restricted diet/with exercise, 13%; high fat diet/no exercise, 31%; high fat diet/with exercise, 19%. Restricting food intake reduced mammary tumor incidence, but had no effect on body weight. Although energy intake was related to mammary tumor incidence, neither body weight nor dietary fat predicted tumor incidence.