Changes of beta-casomorphin content in human milk during lactation

Milk is the best, complete food important for the development and nourishment of a neonate. Except for nutrients, milk contains biologically active opioid peptides derived from beta-casein, named beta-casomorphins (BCMs), which can exert effects in the gastrointestinal tract as well as in the whole body of neonates. The content of beta-casomorphins in human milk during maturation phases has not been studied so far. The aim of this study was to determine the content of beta-casomorphin-5 and -7 in human milk in different phases of lactation. A significantly higher concentration of both beta-casomorphins was found in colostrum than in mature milk. The concentration of beta-casomorphin in milk collected in the second month of lactation was similar to the level obtained in the fourth month of lactation. The content of beta-casomorphins in human milk was observed with the period of lactation. The level of opioid peptides may depend on the function of these peptides in neonate's body and may be associated with the maturation process.     

Coenzyme Q10 in maternal plasma and milk throughout early lactation

In contrast to other lipophilic antioxidants Coenzyme Q10 originates from food intake as well as from endogenous synthesis. The CoQ10 concentration and lipid content of maternal milk and maternal plasma was investigated during early lactation. Breast milk was obtained from 23 women: A: colostrums (24-48 hours postpartum), B: transitional milk (day 7 pp), C: mature milk (day 14 pp). At the same time capillary blood specimens were collected. Milk and plasma were stored at -84 degrees C until CoQ10 was analysed after hexane extraction by HPLC. The lipid content was determined by PAP-analysis of cholesterol. The plasma content of CoQ10 was the highest soon after delivery (A: 1.29, B:1.20, C:1.07 pmol/microl; Wilcoxon p < 0.05 A vs. C and B vs. C). This tendency was still evident after lipid-adjustment (A:209, B:180, C:175 micromol CoQ10/mol cholesterol; Wilcoxon p < 0.01 A vs. B and C). The level of CoQ10 in milk showed a gradual decline during early lactation (A:0.80, B:0.57, C:0.44 pmol/microl; Wilcoxon p < 0.02 A vs. B and C). After lipid-adjustment this tendency became even more evident (A: 137, B:86, C:67 micromol CoQ10/mol cholesterol; Wilcoxon p < 0.002 A vs. B and C, p < 0.05 B vs. C). The content of CoQ10 in plasma and milk showed a correlation with early milk (Spearman p < 0.005) but not with mature milk. Although lipid content is low the colostrums is a rich source for the lipophilic antioxidant CoQ10.     

Trace element content in human milk during lactation of preterm newborns

The present study has been finalized to perform the content of Zn, Cu, Cr, Se, Mn, F, Mo, Ni, and B in the preterm human milk over 21 d of lactation. Trace element (TE) contents were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-MS), and median concentrations of Zn, Cu, Cr, Se, Mn, and F observed in preterm milk did not demonstrate significant differences in comparison to levels shown in term milk. A statistical significant difference (p<0.05) has been found among Mo, Ni, and B content in preterm milk for every stage of lactation. TE content of infant blood founded concentrations of Mo in preterm babies significantly (p<0.01) lower than in term offsprings. Similar values of other TE content were obtained in blood of preterm, and term newborns. These findings point to the need for a considerable reassessment of the existing dietary recommendation for Mo content in infant feeding.     

Alteration of the N-glycome of bovine milk glycoproteins during early lactation

Milk provides nutritional, immunological and developmental components for newborns. Whereas identification of such components has been performed by targeting proteins and free oligosaccharides, structural and functional analyses of the N-glycome of milk glycoproteins are scarce. In this study, we investigated, for the first time, the alterations of the bovine milk N-glycome during early lactation (1 day, 1, 2, 3 and 4 weeks postpartum), characterizing more than 80 N-glycans. The glycomic profile of colostrum on day 1 after calving differed substantially from that in other periods during early lactation. The proteins in colostrum obtained 1 day postpartum were more highly sialylated than milk samples obtained at other time points, and the N-glycolylneuraminic acid (Neu5Gc)/N-acetylneuraminic acid (Neu5Ac) ratio was significantly higher on day 1, showing a gradual decline with time. In order to dissect the N-glycome of colostrum, alterations of the N-glycosylation profile of major bovine milk proteins during the early lactation stage were elucidated, revealing that the alteration is largely attributable to qualitative and quantitative N-glycosylation changes of IgG, the major glycoprotein in colostrum. Furthermore, by preparing and analyzing IgGs in which the N-glycan structure and subtypes were well characterized, we found that the interaction between IgG and FcRn was not affected by the structure of the N-glycans attached to IgG. We also found that bovine FcRn binds IgG(2) better than IgG(1) , strongly suggesting that the role of FcRn in the bovine mammary gland is to recycle IgG(2) from the udder to blood, rather than to secrete IgG(1) into colostrum.     

Asian elephant (Elephas maximus) milk composition during the first 280 days of lactation

Milk samples (n = 10) taken during the first 280 days of lactation from one Asian elephant were examined for nutrient composition including total solids, protein, fat, ash, α-tocopherol, and retinol levels. Total solids averaged 19.7 ± 2.7% SD (range 15.0–23.3). Percent protein remained fairly stable throughout this portion of lactation and averaged 3.4 ± 0.3% (range 3.0–.4.0). Ash content averaged 0.54 ± 0.03%. Milk fat and fat soluble vitamin levels varied considerably with a suggestion of a cyclic pattern. Fat content of milk averaged 7.6 ± 2.6% (range 3.9–.12.1); α-tocopheral levels averaged 0.33 ± 0.12 μg/ml; and retinol levels averaged 0.46 ± 0.1 μg/ml. © 1994 Wiley-Liss, Inc.     

Variation in the lack of polyadenylation of the rat milk protein mRNAs during the lactation cycle

Translationally active milk protein mRNAs were found as nonpolyadenylated mRNAs in the rat mammary gland during pregnancy, lactation and involution. Analyses of whey protein mRNA and casein mRNA with the corresponding cDNAs showed that the lack of polyadenylation of these mRNAs at different time points of the lactation cycle is not consistent with the hypothesis that polyadenylation may be incomplete in the mammary gland when large amounts of mRNA are synthesized. The fraction of whey protein mRNA and casein mRNA that lacked polyadenylation was inversely proportional to the concentration of each sequence in the tissue during pregnancy, lactation and involution. A model is proposed to explain the finding that in each animal the ratio of casein mRNA to whey protein mRNA was similar in polyadenylated RNA and in nonpolyadenylated RNA at all stages of the lactation cycle.     

Prolactin heterogeneity in the serum and milk during lactation

Prolactin heterogeneity in serum and milk were separated using Sephadex G-100. Three components were present in serum from lactating women with the following proportions: “void volume” -13.4%, “big” - 26.4%, and “little” - 60.3%. Milk from the same subjects did not contain “big” prolactin. Over 90% of the prolactin found in milk was “little” prolactin. The “little” prolactin in milk may not be similar to the “little” prolactin in the serum.     

Gangliosides in bovine milk. Changes in content and distribution of individual ganglioside levels during lactation.

Bovine milk undergoes changes in its ganglioside contents during the different stages of lactation. These contents are higher in colostrum (7.5 mg of lipid-bound NeuAc/kg) than in transitional (2.3 mg) or mature (1.4 mg) milk. The sialic acid content of milk follows a similar profile to that of gangliosides with the highest content during the first few days post partum followed by a gradual decrease towards the end of the period studied. When the individual distribution of gangliosides was examined throughout the course of lactation, several changes were also found. GD3 is the major ganglioside (about 60-70%) found; its content decreases from the first to the fifth day, increasing towards the end of the period considered. GM3, GD3 and GT3, sialyllactosylceramide-containing gangliosides account for 80-90% of the total lipid-bound NeuAc content. The most striking change in the ganglioside pattern was the gradual increase in G3.     

Variation of loganin content in Cornus officinalis fruits at different extraction conditions and maturation stages

Efficient preparation of loganin from Cornus officinalis fruits was investigated. First, effect of extraction conditions on loganin yield was measured. The loganin content in C. officinalis extract was greatly affected by ethanol concentration and extraction time whereas extraction temperature exerted relatively little effect. Response surface methodology with Box–Behnken design suggested optimized extraction condition for maximum loganin yield as ethanol concentration, 32.0%; temperature 46.2 °C and extraction time, 46.7 min, which yielded 10.4 μg loganin/mg dried fruit. Next, the effect of maturation stage of C. officinalis fruits on loganin content was investigated. The loganin content in the extract of C. officinalis fruits was decreased as the maturation process. The loganin content in the unripe fruits was 18.0 μg/mg extract whereas reduced to 13.3 μg/mg extract for ripe fruits. Taken together, our present study suggested the importance of extraction condition and maturation stages for efficient preparation of loganin from C. officinalis fruits.     

Quantitation of milk proteins and their mRNAs in rat mammary gland at various stages of gestation and lactation.

The content of alpha-lactalbumin and three species of caseins, 42K, 29K, and 25K, have been measured along with the levels and activities of their mRNAs in the rat mammary gland. Changes in these values were followed during gestation and lactation. An increment of 3- to 4-fold over the virgin level was observed for both alpha-lactalbumin and 42K casein during the 1st day of gestation. From this point on, the level of 42K remained unchanged during the 1st week of gestation and increased thereafter. After the increment of the 1st day, the alpha-lactalbumin content decreased rapidly during the 2nd day of gestation, continued to decrease more slowly until the 12th day, and then started to increase thereafter. During the 2nd and 3rd week of gestation. the amounts of alpha-lactalbumin within the gland increased continuously but not uniformly and caseins accumulated rapidly with a tendency to plateau around the 13th to 16th day of gestation. The relative proportions remained, respectively, 42K greater than 29K greater than 25K greater than alpha-lactalbumin until parturition. At the onset of lactation, both alpha-lactalbumin and casein content increased sharply, the relative proportion for caseins changed to 42K greater than 25K greater than 29K greater than alpha-lactalbumin and remained so throughout the lactation period. alpha-Lactalbumin and casein mRNA activity, as judged by the wheat germ translational system, remained unchanged during the 1st week of gestation, then showed a steady but not uniform increase from the 7th day of gestation until parturition. These activities increased sequentially during lactation, alpha-lactalbumin reaching a plateau by the 1st week, caseins between the 1st and 2nd week, and other mRNAs by the end of the 2nd week of lactation. By the 21st day of lactation, the activity of all mRNA had declined. The levels of alpha-lactalbumin mRNA and 16 S doublet casein mRNA sequences measured with the cDNA probes increased by about 8-fold for alpha-lactalbumin mRNA and 6-fold for casein mRNA during the 1st week of gestation. These levels declined slightly early in the 2nd week and then continued to increase until parturition with a shoulder in the levels around the 13th to 16th day. During lactation, these levels increased until the 8th to 12th day and from then on declined. The content of alpha-lactalbumin and caseins, as well as the measurement of sequences and activities of their mRNAs, showed that in the rat mammary gland these differentiated functions are already expressed at the onset of gestation. Both concentration and activity of mRNA are out of phase with protein levels during the 1st week of gestation but they remain in phase thereafter.     

Variation of DNA polymerase activities and DNA synthesis in mouse mammary gland during pregnancy and early lactation

The rate of DNA synthesis and the activity of DNA polymerases and thymidine kinase were measured during the endocrine-regulated cellular growth and differentiation of mouse mammary gland. Using specific assays, the activity of the DNA polymerases, alpha, beta and gamma, was determined in tissue extracts of mammary glands of mice at various stages of pregnancy and early lactation. In addition, extracts of the mammary tissue of virgin, mid-pregnant and early lactating mice were fractionated on sucrose density gradients, and the activity of DNA polymerase alpha and beta was assayed in the gradient fractions. It was demonstrated that the activity of DNA polymerase alpha varied considerably during pregnancy and after parturition, showing peaks on day 12 of pregnancy and days 3-4 of lactation. In pregnancy, there was an apparently parallel correlation between the amount of DNA-polymerase-alpha activity and the rate at which the cells incorporated labelled thymidine into DNA, but the relationship was less clearly expressed during early lactation. The activity of the DNA polymerases, beta and gamma, as well as that of thymidine kinase showed little variation during these periods. Thus, in the developing mammary gland, no correlation was found between DNA synthesis and the activity of the DNA polymerases, beta and gamma, or thymidine kinase.     

Lactoperoxidase and thiocyanate contents of goats' milk during lactation

The lactoperoxidase level in milk from 10 goats throughout a 150 d lactation period was 1.55 units/ml, with a range of 0.05-3.55 units/ml for invidiual samples. Samples obtained 0–24 h after kidding exhibited the lowest mean concentration (0.50 units/ml). Mean thiocyanate content was 4.03 ppm, with a range of 0.67-11.17 ppm for indidual samples.     

Leptin treatment during lactation increases transfer of iodine through the milk

We have previously shown that protein restriction during lactation is associated with changes in iodine secretion into the milk and that a pup's serum leptin concentration was increased at the end of lactation. So, here we evaluate whether leptin treatment during lactation affects iodine transfer through the milk to the pups. Lactating rats were divided into two groups: the leptin (Lep) group, single injected with recombinant rat leptin (8 microg/100g of body weight, daily for 3 consecutive days), and the control (C) group that received the same volume of saline. We studied iodine transfer to the pups through the milk on Days 4, 12 and 21 of lactation. In those days, the dams were separated from their pups for 4 h. Then, the mothers received an injection of 131I (2.22x10(4) Bq ip) and the pups were allowed to nurse for 2 h. The animals were sacrificed 2 h later. Leptin, total serum T3 and total serum T4 concentrations were higher (P<.05) in pups of Lep mothers only on Day 4, suggesting a higher transfer of leptin through the milk at this period, probably with a direct stimulatory effect on thyroid hormone secretion. In other periods, however, even without a detectable increase in a pup's serum leptin concentration, maternal leptin administration increased the pup's thyroid iodine uptake (Day 12, 39%; Day 21, 34%), probably caused by a higher transfer of iodine through the milk, since they had a higher gastric content of 131I on Days 12 (31%) and 21 (128%).     

Transcervical collection of equine conceptuses between 10 and 16 days after ovulation

To recover intact Day-10.5 to Day-16.5 equine conceptuses (Day 0 = ovulation), a rigid catheter was used for 131 collections from donor mares diagnosed pregnant by ultrasonography. A total of 139 conceptuses were recovered, comprising 124 singletons, six pairs of twins and one set of triplets. Of these, 120 (86%) were intact after the collection, 14 (10%) had collapsed, and in five cases (4%), collapsed trophoblastic membranes were surrounded by an intact capsule. The recovery rate of intact conceptuses ranged from 99% on Days 10.5 to 12.5 to 40% on Day 16.5. More uterine flushes per recovery were needed to collect conceptuses on Day 14.5 than on Days 10.5 and 11.5 (x +/- SEM : 3.1 +/- 0.5 vs 1.4 +/- 0.1 and 1.3 +/- 0.2 flushes, respectively, P<0.05), and the total volume of flushing medium used was greater on Day 14.5 than on Days 10.5, 11.5 and 12.5 (1040 +/- 193 vs 406 +/- 49, 396 +/- 48 and 499 +/- 59 ml, respectively, P<0.01). Seventy of the 100 mares inseminated at the first estrus following embryo collection became pregnant, indicating that the technique used had no major effect on subsequent fertility.     

Intermittent suckling enables estrus and pregnancy during lactation in sows: effects of stage of lactation and lactation during early pregnancy

Previously we demonstrated that pre-ovulatory LH and post-ovulatory progesterone (P4) concentrations in plasma were low and embryo development was retarded when sows were induced to ovulate during lactation by submitting them to intermittent suckling (IS). The present study investigated whether this was due to: (1) stage of lactation when IS was initiated, and (2) continuation of IS post-ovulation. Multiparous Topigs40 sows were studied under three conditions: conventional weaning at Day 21 of lactation (C21; n = 30), intermittent suckling from Day 14 of lactation (IS14; n = 32), and intermittent suckling from Day 21 of lactation (IS21; n = 33). Sows were separated from piglets for 12 h daily during IS. IS sows were either weaned at ovulation or 20 d following ovulation. One-third (21/63) of the IS21 and C21 sows had already ovulated or had large pre-ovulatory follicles at Day 21 and were excluded from further study. Initiation of IS at Day 14 instead of Day 21 of lactation tended to reduce P4 at 7 d post-ovulation (P = 0.07), did not affect pregnancy rate, and tended to reduce embryo survival (P = 0.06). Continuation of IS during pregnancy resulted in lower P4 at 7 and 12 d post-ovulation, tended to reduce embryo weight and pregnancy rate (P < 0.10), whereas embryo survival was not affected. This study presents data for a population of sows in which follicle growth and ovulation are easily triggered under suckling conditions. Further, when these sows are bred during lactation, initiation of IS at 21 rather than 14 d of lactation with weaning at ovulation yields the most desirable reproductive performance.     

Selective changes in gangliosides of human milk during lactation: a molecular indicator for the period of lactation

Gangliosides of human milk from women at various periods of lactation were analyzed. GD3 in colostrum, particularly in the early period of lactation, was the major ganglioside, and the molar ratio of GM3 to GD3 was 0.2-0.3 in the milk at 2-6 days postpartum. In contrast, milk from women at 60-390 days postpartum contained GM3 as the major ganglioside and the molar ratio of GM3 to GD3 was more than 3. Milk at 8-40 days postpartum represented an intermediate stage in terms of the ratio of GM3 to GD3. The selective change in the molar ratio of gangliosides was observed as a phenomenon common to all human milk from different individuals at different periods of lactation, indicating that the periods of lactation can be defined on the basis of the ratio. Since glycolipids in human milk are preferentially localized in the milk fat globule membrane, which is derived from the plasma membrane of epithelial cells in the mammary gland, the changes in the ganglioside composition reported in this communication may reflect a qualitative change of the cells in the mammary gland.