Increased cholesterol 7alpha-hydroxylase expression and size of the bile acid pool in the lactating rat

Maximal bile acid secretory rates and expression of bile acid transporters in liver and ileum are increased in lactation, possibly to facilitate increased enterohepatic recirculation of bile acids. We determined changes in the size and composition of the bile acid pool and key enzymes of the bile acid synthetic pathway [cholesterol 7alpha-hydroxylase (Cyp7a1), sterol 27-hydroxylase (Cyp27a1), and sterol 12alpha-hydroxylase (Cyp8b1)] in lactating rats relative to female virgin controls. The bile acid pool increased 1.9 to 2.5-fold [postpartum (PP) days 10, 14, and 19-23], compared with controls. A 1.5-fold increase in cholic acids and a 14 to 20% decrease in muricholic acids in lactation significantly increased the hydrophobicity index. In contrast, the hepatic concentration of bile acids and small heterodimer partner mRNA were unchanged in lactation. A 2.8-fold increase in Cyp7a1 mRNA expression at 16 h (10 h of light) demonstrated a shift in the diurnal rhythm at day 10 PP; Cyp7a1 protein expression and cholesterol 7alpha-hydroxylase activity were significantly increased at this time and remained elevated at day 14 PP but decreased to control levels by day 21 PP. There was an overall decrease in Cyp27a1 mRNA expression and a 20% decrease in Cyp27a1 protein expression, but there was no change in Cyp8b1 mRNA or protein expression at day 10 PP. The increase in Cyp7a1 expression PP provides a mechanism for the increase in the bile acid pool.     

Prolactin inhibition in lactating rats changes leptin transfer through the milk.

Malnutrition during lactation reduces milk production and changes pup's leptin serum levels. To test prolactin role in this nutritional state, we evaluated whether prolactin suppression during lactation changes serum leptin in dams, its transfer through the milk, and pup's serum leptin. Lactating rats were treated with bromocryptine (1 mg/twice a day, s.c.) or saline three days before sacrifice (days 2-4 or days 19-21). Food intake and body weight were measured until sacrifice (4th and 21st day). Serum prolactin and leptin were determined by radioimmunoassay. Bromocryptine injected dams had lower serum prolactin and milk production as expected. The mothers presented lower food ingestion (day 21: -25%), lower body weight (day 4: -12%; day 21: -10%), higher serum leptin (day 4: +68%), lower milk leptin on the 4th day (11 times) and higher (8 times) on the 21st day. The offspring of bromocryptine-treated mothers presented lower body weight in both periods of lactation and lower serum leptin on the 4th day (-40%) and higher on the 21st day (+37%) of lactation. We suggest that prolactin, through its effect on leptin secretion into the milk, may play an important role in signalizing maternal nutritional status to the pups.     

Localization and expression of BCAT during pregnancy and lactation in the rat mammary gland

During lactation, branched-chain aminotransferase (BCAT) gene expression increases in the mammary gland. To determine the cell type and whether this induction is present only during lactation, female rats were randomly assigned to one of three experimental groups: pregnancy, lactation, or postweaning. Mammary gland BCAT activity during the first days of pregnancy was similar to that of virgin rats, increasing significantly from day 16 to the last day of pregnancy. Maximal BCAT activity occurred on day 12 of lactation. During postweaning, BCAT activity decreased rapidly to values close to those observed in virgin rats. Analyses by Western and Northern blot revealed that changes in enzyme activity were accompanied by parallel changes in the amount of enzyme and its mRNA. Immunohistochemical studies of the mammary gland showed a progressive increase in mitochondrial BCAT (mBCAT)-specific staining of the epithelial acinar cells during lactation, reaching high levels by day 12. Immunoreactivity decreased rapidly after weaning. There was a significant correlation between total BCAT activity and milk production. These results indicate that the pattern of mBCAT gene expression follows lactogenesis stages I and II and is restricted to the milk-producing epithelial acinar cells. Furthermore, BCAT activity is associated with milk production in the mammary gland during lactation.     

Milk secretion in the rat: progressive changes in milk composition during lactation and weaning and the effect of diet.

1. Progressive changes in the composition of milk from rats has been studied from day 0 to 20 of lactation and for 3 days following separation of the dams and pups at day 20 post partum. 2. The changes in concentration of Na, K and lactose suggested that secretion both prepartum and following weaning occurred by a paracellular mechanism whereas a transcellular pathway existed during established lactation. 3. The concentration of total protein and casein increased gradually throughout lactation. In contrast, the concentration of serum albumin increased and transferrin decreased markedly during early lactation. The fat content of milk declined 3-fold within 5 days of birth but the concentration of Ca, Mg and inorganic P increased. The concentration of each of these milk constituents remained constant during established lactation. 4. Following weaning the pronounced decline in lactose, K and inorganic P was negatively correlated with an increase in all other milk constituents except fat. 5. Rats fed a low energy diet produced milk with a lower fat content but with an unaltered concentration of protein and carbohydrate. The growth rate of these litters was similar for the first 5 days of lactation when compared to litters from dams fed a high energy diet. The growth rate of litters thereafter and following weaning was greater for rats fed a high energy diet.     

Levels of cellular retinol-binding proteins in the small intestine of rats during pregnancy and lactation

The movement and metabolism of vitamin A is dependent on a number of specific carrier proteins. The small intestine contains both cellular retinol-binding protein (type two) (CRBP(II], restricted to the villus-associated enterocytes, and cellular retinol-binding protein (CRBP), present primarily in supporting mesenchymal cells. The content of these proteins in the small intestine of prepartum and postpartum Sprague-Dawley rats was determined by radioimmunoassay. Levels of CRBP(II), but not CRBP, changed dramatically during this period. Total content of CRBP(II) in the small intestine rose precipitously in late pregnancy and continued to rise throughout lactation to a peak at day 21 postpartum more than 300% greater than in nulliparous, nonpregnant controls. In contrast, total small intestinal weight and CRBP content increased only approximately 100% from late pregnancy to day 21 of lactation. CRBP(II) concentration in the proximal and middle segments of small intestine (expressed on a g wet tissue, mg protein, or mg DNA basis) remained at control levels through day 17 of pregnancy, increased 50-100% in late pregnancy, then rose markedly at parturition to levels two- to threefold greater than controls. CRBP(II) concentration was then maintained at a relatively constant elevated level during the remainder of lactation, but decreased markedly after weaning, approaching control levels within 1 week. The concentrations of CRBP(II) in enterocytes isolated from the proximal two-thirds of the small intestine from rats on day 20 of pregnancy and days 1 and 16 of lactation, expressed on a mg DNA basis, were similar and approximately 60% greater than controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolic response to starvation in late pregnant rats. I. Maternal response

The aim of the present study was to examine effect of prolonged fasting on muscle glycogen and triglyceride concentration as well as on non-protein nitrogen excretion with urine in late pregnant rats. They were divided into four groups: I--fed, pregnant for 21 days, II--fasted for one day (from 20 to 21 day of pregnancy), III--fasted for two days (from 19 to 21 day) and IV--fasted for three days (from 18 to 21 day). The concentration of glycogen and triglycerides was determined in the following tissues: the white and red layers of the vastus lateralis, the soleus, the diaphragm, the heart and the liver. The urine was collected in each group 24 h (from 20 to 21 day). It has been found that concentration of glycogen in the leg muscles is reduced by about 50% and in the diaphragm by 75% already after 24 h fasting and then remains stable. The concentration of glycogen in the heart increases after one day of fasting and then returns to the control value. The effect of fasting on the concentration of triglycerides in the tissues depends on a tissue studied. It decreases gradually in the white vastus, and in the soleus only on the third day. It is elevated during the first two days of fasting in the red vastus, diaphragm and liver and returns to the control level on the third day. The fasting doubled the concentration of triglycerides in the heart. The urinary urea, creatinine, and uric acid excretion decreases and ammonia excretion increases during fasting. The results obtained indicate that the late gestation does not alter response of muscle glycogen metabolism to fasting as compared to the male rats. It does effect metabolism of triglycerides.     

Maternal Undernutrition During Lactation: Effect on Amino Acids in Brain Regions of Offspring

Sprague-Dawley dams were fed either a protein-calorie deficient or control diet from day 5 to day 21 after parturition. The concentrations of seven amino acids (aspartate, glutamate, gamma-aminobutyric acid, glycine, glutamine, serine, and taurine) were determined in brain regions from 17-day-old undernourished offspring and from 35-day-old rehabilitated rats. The brain regions examined were the cortex, cerebellum, corpus striatum, hippocampus, hypothalamus, brainstem, and midbrain. At 17 days of age, taurine was the amino acid with the highest concentration, whereas at 35 days glutamate had the highest concentration. This change was due to the fact that the concentration of taurine decreased significantly in all brain regions between 17 and 35 days, whereas the concentration of glutamate remained high or increased somewhat in all brain regions except the hypothalamus and brainstem. When the age-matched offspring of control and undernourished rats were compared, several interesting and significant differences were found. The concentrations of glutamate and aspartate were significantly lower (decreased 16-34%) in the cerebellum, brainstem, cortex, and midbrain in 17-day-old undernourished rats. The aspartate level was also significantly decreased in the corpus striatum and hypothalamus in 17-day-old offspring. However, the deficiencies of aspartate and glutamate were transient and reversible. In contrast, the concentration of taurine was increased in the hypothalamus (31%) and hippocampus (12-33%) at both 17 and 35 days of age and in the midbrain (17%) at 17 days. Other transient abnormalities in amino acid levels were found in undernourished offspring. The results of these experiments suggest that undernutrition during lactation causes delayed CNS development, which is manifested in altered concentrations of the neurotransmitters aspartate, glutamate, and taurine.     

Expression, activity, and localization of hormone-sensitive lipase in rat mammary gland during pregnancy and lactation

We examined the presence of hormone-sensitive lipase (HSL) in mammary glands of virgin, pregnant (12, 20, and 21 days), and lactating (1 and 4 days postpartum) rats. Immunohistochemistry with antibody against rat HSL revealed positive HSL in the cytoplasm of both alveolar epithelial cells and adipocytes. In virgin rats, immunoreactive HSL was observed in mammary adipocytes, whereas diffuse staining was found in the epithelial cells. Positive staining for HSL was seen in the two types of cells in pregnant and lactating rats. However, as pregnancy advanced, the staining intensity of immunoreactive HSL increased in the epithelial cells parallel to their proliferation, attaining the maximum during lactation. An immunoreactive protein of 84 kDa and a HSL mRNA of 3.3. kb were found in the rat mammary gland as in white adipose tissue. Both HSL protein and activity were lower in mammary glands from 20 and 21 day pregnant rats than from those of virgin rats, although they returned to virgin values on days 1 and 4 of lactation. Mammary gland HSL activity correlated negatively to plasma insulin levels. Immunoreactive HSL and HSL activity were found in lactating rats' milk. The observed changes indicate an active role of HSL in mammary gland lipid metabolism.     

Lactogenesis in the rat: an ultrastructural study of the initiation of the secretory process.

Three specimens were taken from mammary glands of rats killed on the 18th and 21st days of pregnancy and on the 1st day of lactation. Ultrastructural features of the tissue were compared among rats within and between the two stages of development. The similarity among specimens from the same rats made feasible a comparison of serial biopsies obtained every 4 hr, starting on the afternoon of the 21st day of pregnancy. From the 18th to the 21st days of pregnancy, a marked increase in the amount of rough endoplasmic reticulum occurred. The alveolar cells of rats killed on both days and in biopsies obtained at 17 and 13 hr before partuirtion contained abundant small lipid droplets and vacuoles containing many protein granules with little clear fluid (stasis vacuoles). Alveolar lumina were distended with secretion by 17 hr before parturition. Between 8 and 12 hr. before parturition, the accumulated protein and lipid were rapidly extruded from the alveolar cells despite evidence of continued biosynthesis. It is suggested that active transport processes are initiated independently of milk synthesis before parturition.     

Lactation influences the serum level of leptin and growth hormone during the daily bathyphase in ewes

The aim of the study was to investigate the influence of early lactation on leptin and growth hormone (GH) during bathyphase. Forty lactating Sarda ewes were divided into two equal groups on the basis of their milk production levels: HIGH (>1100 g/day) and LOW (<900 g/day). From the 5th to the 110th day after lambing, every 15 days, body condition score (BCS) was recorded and milk samples were collected. At the same data point, blood sampling was performed and leptin, GH and, Non-Esterified Fatty Acids (NEFA) were assessed. On milk, fat and proteins were determined. Statistical differences were observed in BCS, leptin, GH, NEFA and fat concentration in milk between the two groups. BCS was lower in high group and decreased from the 20th to the 90th day of lactation. Leptin was higher in low group and increased from the 50th and the 65th day of lactation, in low and high groups, respectively. GH and NEFA were higher in high group and decreased from the mild lactation. In high group, BCS and milk yield were negatively correlated and leptin was negatively correlated with GH and NEFA. In low group, leptin was positively correlated with BCS and negatively correlated with the all studied parameters. GH and NEFA were positively correlated with both groups. In conclusion, milk yield had an effect on the leptin and GH plasma values recorded during their bathyphase.     

Taurine and β-alanine intraperitoneal injection in lactating mice modifies the growth and behavior of offspring

Taurine, one of the sulfur-containing amino acids, has several functions in vivo. It has been reported that taurine acts on γ-aminobutyric acid receptors as an agonist and to promote inhibitory neurotransmission. Milk, especially colostrum, contains taurine and it is known that milk taurine is essential for the normal development of offspring. β-Alanine is transported via a taurine transporter and a protein-assisted amino acid transporter, the same ones that transport taurine. The present study aimed to investigate whether the growth and behavior of offspring could be altered by modification of the taurine concentration in milk. Pregnant ICR mice were separated into 3 groups: 1) a control group, 2) a taurine group, and 3) a β-alanine group. During the lactation periods, dams were administered, respectively, with 0.9% saline (10?ml/kg, i.p.), taurine dissolved in 0.9% saline (43 mg/10?ml/kg, i.p.), or β-alanine dissolved in 0.9% saline (31 mg/10?ml/kg, i.p.). Interestingly, the taurine concentration in milk was significantly decreased by the administration of β-alanine, but not altered by the taurine treatment. The body weight of offspring was significantly lower in the β-alanine group. β-Alanine treatment caused a significant decline in taurine concentration in the brains of offspring, and it was negatively correlated with total distance traveled in the open field test at postnatal day 15. Thus, decreased taurine concentration in the brain induced hyperactivity in offspring. These results suggested that milk taurine may have important role of regulating the growth and behavior of offspring.     

Circulating immunoreactive inhibin, gonadotropin, and prolactin levels during pregnancy, lactation, and postweaning estrous cycle in the rat

Serum inhibin levels were measured by heterologous RIA during pregnancy, lactation, and the post-weaning estrous cycle in the rat and correlated with changes in serum FSH and LH and prolactin. Blood was serially collected by cardiac puncture under light ether anesthesia from adult Sprague-Dawley rats on alternate days throughout the experimental period. For the first 8 days of pregnancy, immunoreactive inhibin levels remained high, then gradually decreased to reach a nadir at Day 16, and subsequently rose steeply until parturition. The pattern of serum immunoreactive inhibin levels during early pregnancy does not support a corpus luteum source and the dramatic rise from Day 16 to Day 22 correlates with the recommencement of follicular development in the ovary. Inhibin levels decreased rapidly on the day after birth and were suppressed until Day 8 of lactation, slowly increasing thereafter to reach a plateau from Day 14 until weaning (Day 22.5 of lactation). These changes in inhibin levels positively correlated with LH and FSH and negatively with prolactin, and are consistent with an ovarian source for inhibin associated with the recommencement of follicular development resulting from the diminution of the suckling stimulus. Immediately after weaning, serum immunoreactive inhibin levels showed a 4-day cyclic pattern corresponding to the estrous cycle identified by vaginal smear. Inhibin levels peaked on the day of proestrus, reached a nadir on the day of estrus, and rose slowly during metestrus and diestrus to a new peak at proestrus. Serum FSH levels showed an inverse correlation to inhibin levels consistent with a feedback relationship with inhibin.     

Interaction of late pregnancy and lactation in rats.

The effect of pregnancy on lactation was studied during the third week of lactational pregnancy in postpartum pregnant rats with a delay in implantation of only 1 day (1d-LP rats). In an experimental design in which the suckling litter was prevented from consuming solid food, lactational performance was estimated by weighing the ten-pup suckling litters on days 16-21 of lactation or by measuring maternal weight loss after a nursing spell on day 21. In 1d-LP rats, food consumption as well as lactational performance was lower than it was in nonpregnant lactating rats (L rats) and pregnant-lactating rats with a normal long delay of implantation of at least 6 days (LP rats). The time spent by the pups sucking at the nipples was not different among the three groups, but the number of milk ejections was diminished in 1d-LP dams. Restriction of daily food supply during days 16 to 21 of lactation diminished lactational performance more strongly in 1d-LP rats than it did in L rats; 1d-LP rats conserved protein stores and mobilized fewer minerals than did L rats. The weight and composition of the litter in vitro were not affected by the food restriction. In pregnant-lactating rats (LP and 1d-LP rats), the number of early resorptions was increased in comparison with pregnant rats, showing that lactation can affect the earlier stages of pregnancy. It was concluded that late pregnancy does not affect nursing behaviour, but suppresses lactation by restricting maternal food intake and mobilization of maternal stores. Measurements in serum indicate a causative role for oestradiol, but not for leptin.     

TAURINE IN DEVELOPING RAT BRAIN: MATERNAL-FETAL TRANSFER OF [35S]TAURINE AND ITS FATE IN THE NEONATE

The transfer of [³⁵] taunne, injected intrapentoneally into pregnant rats (near term), to fetal tissues has been measured. Taurine can enter fetal brain as easily as it can fetal liver. In contrast, it cannot enter mature brain as easily as it can enter mature liver. After birth, [³⁵S] taurine, which had been injected into the dam before birth of the pups, continues to accumulate in the brain of the pups for some days. During the neonatal period, the concentration of taurine is decreasing, but the total pool of taurine in the brain is increasing rapidly. In order to help supply this increasing pool, the taurine present in the brain at birth appears to be conserved and an increasing amount of taurine is synthesized in situ. The net result during the neonatal period of development is that brain taurine specific radioactivity decreases and brain taurine has a very slow rate of turnover.     

Effects of Taurine Supplementation on Hepatic Markers of Inflammation and Lipid Metabolism in Mothers and Offspring in the Setting of Maternal Obesity

Maternal obesity is associated with obesity and metabolic disorders in offspring. However, intervention strategies to reverse or ameliorate the effects of maternal obesity on offspring health are limited. Following maternal undernutrition, taurine supplementation can improve outcomes in offspring, possibly via effects on glucose homeostasis and insulin secretion. The effects of taurine in mediating inflammatory processes as a protective mechanism has not been investigated. Further, the efficacy of taurine supplementation in the setting of maternal obesity is not known. Using a model of maternal obesity, we examined the effects of maternal taurine supplementation on outcomes related to inflammation and lipid metabolism in mothers and neonates. Time-mated Wistar rats were randomised to either: 1) control : control diet during pregnancy and lactation (CON); 2) CON supplemented with 1.5% taurine in drinking water (CT); 3) maternal obesogenic diet (high fat, high fructose) during pregnancy and lactation (MO); or 4) MO supplemented with taurine (MOT). Maternal and neonatal weights, plasma cytokines and hepatic gene expression were analysed. A MO diet resulted in maternal hyperinsulinemia and hyperleptinemia and increased plasma glucose, glutamate and TNF-α concentrations. Taurine normalised maternal plasma TNF-α and glutamate concentrations in MOT animals. Both MO and MOT mothers displayed evidence of fatty liver accompanied by alterations in key markers of hepatic lipid metabolism. MO neonates displayed a pro-inflammatory hepatic profile which was partially rescued in MOT offspring. Conversely, a pro-inflammatory phenotype was observed in MOT mothers suggesting a possible maternal trade-off to protect the neonate. Despite protective effects of taurine in MOT offspring, neonatal mortality was increased in CT neonates, indicating possible adverse effects of taurine in the setting of normal pregnancy. These data suggest that maternal taurine supplementation may ameliorate the adverse effects observed in offspring following a maternal obesogenic diet but these effects are dependent upon prior maternal nutritional background.     

Circulating leptin levels in newborn rats: a significant post- natal developmental effect,independent of dietary polyunsaturated fat levels

Leptin expression exhibits developmental and dietary regulation, but it is unknown whether there is an interaction of the regulation by dietary fat and postnatal development. The purpose of this study was to test the effect of different levels of dietary polyunsaturated fat on circulating leptin levels at different post-natal developmental stages. Pregnant (Sprague-Dawley) rats consumed from day 15 of pregnancy through day 9 of lactation a low fat, (11% of energy; LF) polyunsaturated safflower oil diet. From day 9 of lactation, dams and their respective pups were fed low, moderate (40% of energy; MF) or high (67% of energy; HF) polyunsaturated safflower oil diets to full maturation (56 days). Diets were iso-energetic and iso-nitrogenous. Milk fatty acid content reflected the mothers and pups diet, with 15 to 100 fold less C10:0 and 2.6 to 3.3 fold more C18:2 in MF and HF groups compared to LF diet. In newborn rats through post-natal day 56, levels of polyunsaturated fat in mothers' milk and mothers/pups diet had no effect on the levels of circulating leptin. The post-natal development period significantly affected circulating leptin levels (p < 0.001, 15 days = 56 days > 21 days > 28 days). In summary, the developmental postnatal stage regulates leptin levels, independently of the polyunsaturated fat levels in the diet.     

Copper transport to mammary gland and milk during lactation in rats

The delivery of copper to mammary gland and milk and the effects of lactation were examined in rats. Traces of (67)Cu/(64)Cu(II) were injected intraperitoneally or intravenously into virgin rats or lactating rats (2-5 days postpartum), and incorporation into blood, milk, and tissues was monitored. In virgin rats, most of the isotope first entered the liver and kidney. In lactating rats, almost 60% went directly to the mammary gland. Uptake rates and copper contents of the mammary gland were 20-fold higher in lactation. (67)Cu/(64)Cu appeared in milk and milk ceruloplasmin as rapidly as in mammary tissue and when there was no (67)Cu/(64)Cu-ceruloplasmin in the maternal plasma. Plasma (125)I-labeled albumin entered milk much more slowly. Milk ceruloplasmin (10 mg/l) had 25% of the (67)Cu/(64)Cu. Milk copper was 3.3 mg/l. Thus lactation markedly enhances the avidity of the mammary gland for copper, diverting most of it from liver and kidney to that tissue. Also, the primary source of milk ceruloplasmin is the mammary gland and not the maternal plasma.     

Toxicokinetic Profile of N‐(2‐Aminoethyl)ethanolamine in the Female Wistar Rat and Distribution into the Late Gestation Fetus and Milk

N‐(2‐aminoethyl)ethanolamine (AEEA) caused aneurysms of the great vessels in rats exposed in utero and during the first days post partum, exacerbated by postnatal treatment of the lactating dams (Moore et al., 2012. Birth Defects Res B Dev Reprod Toxicol [95:116‐122]). The purpose of this work was to examine the systemic availability of AEEA during gestation and early lactation. The absorption of AEEA was determined following oral administration to nonpregnant and pregnant female Wistar rats. A single dose administered by gavage (0.5 or 50 mg/kg) on gestation day 18 was rapidly and extensively (>90%) absorbed from the gastrointestinal tract (absorption t_1/2 = 0.1–0.2 hr). Elimination from the plasma followed a biphasic pattern, with a rapid elimination phase (t_1/2 α = 1.6–1.8 hr) followed by a slower phase (t_1/2 β = 16.7–17.3 hr). Following repeated gavage administration during gestation day 17 to 19, ¹⁴C‐AEEA–derived radioactivity readily partitioned into the fetus and was evenly distributed therein, but cleared approximately twofold slower from the fetal blood and tissues than the maternal blood and chorioallantoic placenta. When administered to lactating dams during lactation days 1 to 12, ¹⁴C‐AEEA–derived radioactivity preferentially partitioned into the milk reaching levels that were between 1.6‐ and 2.5‐fold higher than the maternal blood. Although the concentration of AEEA equivalents in the maternal blood remained quite consistent, the concentration in the milk fell by almost 40% between lactation days 4 and 12, probably reflecting an increase in milk production over this same period. We confirm exposure of the offspring to AEEA both in utero and during lactation, but that AEEA does not appear to specifically concentrate in the great vessels.     

Effect of suboptimal nutrition during lactation on milk protein gene expression in the rat

Human milk provides infants with proteins that aid in the prevention of infections and facilitate the digestion and absorption of other nutrients. Maternal diet is not believed to affect the protein concentration of breast milk. However, the maternal factors that regulate the expression of genes for specific milk proteins are not well characterized. We hypothesized that nutrition could be one of the factors. We fed Sprague-Dawley rats five diets representing common nutrient deficiencies and energy deficiency during pregnancy and lactation: low-zinc (Zn; 7 microg/g), low-iron (Fe; 6 microg/g), low-protein (12.5% albumin), pair-fed control diet (lactation only, 20% less kcal) and control diet (Zn, 25 microg/g; Fe, 100 mug/g; protein, 21%) ad libitum. At day 10 of lactation, the mammary gland was removed for RNA extraction. Northern blots of mRNA from the different groups were performed by hybridization with beta-casein and whey acidic protein (WAP) cDNA probes. The expression of beta-casein mRNA in rat mammary gland was significantly (P<.005) increased in the pair-fed group when compared to the control group. The expression of WAP mRNA was also significantly (P<.005) increased in the pair-fed group as well as in the low-Fe group when compared to the control group. The concentration of beta-casein in milk was significantly higher for the low-zinc and the pair-fed groups only. The concentration of WAP in milk was not different among groups. These results suggest that compromised maternal nutrition can affect the expression of two individual milk proteins and may have functional implications with regard to bioactive proteins in milk.     

Milk transfer of inorganic mercury to suckling rats

The transport of mercury into rat milk, and uptake in the suckling offspring was studied after peroral administration of inorganic mercury to lactating control rats, and to rats fed selenite in the diet. On day 8, 9, 10, or 11 of lactation, dams were administered a single oral dose of 0.1, 0.4, 0.7, 1.3, or 5.8 mg Hg/kg bw labeled with 203mercuric acetate. There was a linear relationship between mercury concentrations in dam's plasma and milk. The level of mercury in milk was approximately 25% of the level in plasma. After 3 d, milk levels were reduced to half the levels at 24 h. In the suckling offspring, exposed to mercury via milk during 3 d, the mercury level in blood was approximately 1% of the level in maternal blood. Mercury concentration in milk was linearly correlated to the levels in kidney, liver, and brain in the suckling offspring after 3 d exposure to mercury via milk. Selenite treatment of rats, 1.3 micrograms Se/g diet for 5 mo, resulted in increased transport of mercury to milk, probably because of increased plasma levels of mercury. However, selenite treatment of the dams did not cause any increased tissue levels of mercury in the suckling offspring.