Metabolic proteomics of the liver and mammary gland during lactation

The liver and the mammary gland have complementary metabolic roles during lactation. Glucose synthesized by the liver is released into the circulation and is taken up by the mammary gland where major metabolic products of glucose include milk sugar (lactose) and the glycerol backbone of milk fat (triglycerides). Hepatic synthesis of glucose is often accompanied by β-oxidation in that organ to provide energy for glucose synthesis, while mammary gland synthesizes rather than oxidizes fat during lactation. We have therefore compared enzyme abundances between the liver and mammary gland of lactating Friesian cows where metabolic output is well established. Quantitative differences in protein amount were assessed using two-dimensional differential in-gel electrophoresis. As predicted, the abundances of enzymes catalysing gluconeogenesis and β-oxidation were greatest in the liver, and enzyme abundances in mammary tissue were consistent with fat synthesis rather than β-oxidation.     

Energetics of lactation in harp seals (Phoca groenlandica) from the gulf of St. Lawrence,Canada

 This study reports the findings of an integrated, comprehensive analysis of lactation energetics in harp seals conducted using longitudinal measurements of mass, body composition and milk composition from mother-pup pairs in conjunction with water flux measurements in pups. The nursing period of harp seals is a short, intense and relatively efficient period of energy transfer from mothers to pups. The average daily milk intake for pups was 3.65±0.24 kg which is equivalent to 79.5 MJ of energy. Eighty-one per cent of the energy received in the milk was metabolisable and 66% of the energy was stored by the pups as body tissue. The field metabolic rate of pups was 3.9±0.4 time basal metabolic rate. The pups were growing at a rate of 2.2 kg per day during the nursing period. The distribution of this mass gain varied in terms of tissue composition, depending on the age of the pups, but over the whole nursing period approximately half of the tissue was stored as fat. Harp seal mothers lost an average of 3.1 kg per day during lactation which was composed of 37% water, 50% fat, 11% protein and 2% ash. Mothers spent half of their time during the lactation period actively diving and only one-third of their time on the surface of the ice. Milk compositional changes followed the normal phocid pattern with increasing fat content and decreasing water content as lactation progressed. The mean mass transfer efficiency was 73%. However, this value cannot be used without qualification because female harp seals in this study fed to varying degrees, consuming an estimated 0–4.8 kg of fish per day. Feeding does not appear to be required in order to achieve the energy requirements for lactation, given the energy stores possessed by females, and some females do fast through the entire period so feeding may be considered opportunistic in nature. Accepted: 25 April 1996     

Nursing stimulation is more than tactile sensation: It is a multisensory experience

Novel sensory experiences, particularly those associated with epochal developmental events like nursing alter cortical representation, affecting memory, perception and behavior. Functional MRI was used here to test whether the sensoricortical map of the ventrum is modified during lactation. Three stimuli were used to drive cortical activation in primiparous rats: natural, artificial suckling stimulation and general mechanical rubbing of the skin of the ventrum. These stimuli significantly activated the somatosensory cortex of dams. Of the three stimuli, artificial and pup suckling robustly activated much of the cerebrum, most notably the visual, auditory and olfactory cortices. Surprisingly, activation occurred even in the absence of pups, with artificial suckling. This finding suggests that incoming information from a single modality was sufficient to drive activity of others. Enhanced sensitivity across the cortical mantle during nursing may help the dam to perceive, process, and remember stimuli critical to the care and protection of her young.     

Silymarin BIO-C, an extract from Silybum marianum fruits, induces hyperprolactinemia in intact female rats

Breastfeeding is widely acknowledged to have important health benefits for infants and mothers. Milk thistle (Silybum marianum fruits) has been recently proposed to be used by nursing mothers for stimulating milk production; however, the mode of action of this herbal drug is still unknown. In this paper, we have evaluated the effect of a micronized standardized extract of S. marianum (Silymarin BIO-C^®=Piùlatte^®) on the serum levels of prolactin in female rats. A 14-day treatment with Silymarin BIO-C^® (25–200 mg/kg, given orally) increased, in a dose dependent manner, the serum prolactin levels. Moreover, after a 66-day discontinuation of Silymarin BIO-C^® treatment, prolactin levels were still significantly elevated although we observed a trend to decrease that was counteracted by a further 7-day treatment with Silymarin BIO-C^®. Bromocriptine, a dopamine D₂ receptor agonist, (1–10 mg/kg, os) significantly and in a dose dependent manner, reduced the serum prolactin levels; bromocriptine, at the dose of 1 mg/kg, significantly reduced the high serum prolactin levels induced by Silymarin BIO-C^®. In conclusion, we have shown that an extract from S. marianum fruits significantly increases circulating prolactin levels in female rats; this effect seems to involve, at least in part, dopamine D₂ receptors.     

Proliferation and apoptosis in subcutaneous adipose tissue of lactating cows with different genetic merit for milk yield

The aim of this study was to investigate the adipocyte size and fate in subcutaneous fat (scAT) of cows diverging for genetic merit at mid lactation stage, when anabolic activity increases and animals are in a state of positive energy balance. Twenty mid lactation cows (180 ± 20 days in milk) grouped according to the Estimated Breeding Values (EBV) for milk yield in plus (EBVp) and minus (EBVm) variants were selected. Average of adipocytes area, proliferation and apoptotic labelling index as well as DLK-1 expression, a marker of pre-adipocytes, were immunohistochemically evaluated in scAT biopsies. In EBVp cows, the BCS was lower (P < 0.01) whereas milk yield, protein, fat yield (P < 0.001) and plasma free fatty acid concentration (P < 0.05) were higher. The scAT of EBVp cows showed a significantly (P < 0.001) higher frequency between 500 and 3000 μm² classes in comparison to EBVm cows, that showed a significantly (P < 0.01) higher apoptotic labeling index. The immunohistochemical reaction showed DLK-1 positivity in scAT of EBVp cows. Taking together, the data indicate a link between milk yield genetic merit of cows, scAT morphology and function, suggesting greater dynamics and metabolic flexibility in EBVp cows.     

Lactoferrin concentrations in goat milk throughout lactation

Lactoferrin is an iron-binding glycoprotein and is considered a major part of the non-specific disease resistance complex in the mammary gland. For cows, the influence of physiological factors on the lactoferrin concentration in milk has been reported. In addition, lactoferrin concentrations have been demonstrated to be proportional to somatic cell counts (SCC) in cows milk. In this study, we aimed to analyse the effects of lactational stage, lactation number and SCC in 19 goats throughout an entire lactational period. Lactoferrin concentrations in weekly composite milk samples were analysed with a competitive ELISA developed for caprine lactoferrin. Maximal lactoferrin concentrations were observed in the colostral samples (387 ± 69 μg/ml). In the following week, less than 20% of these concentrations were observed (62 ± 25 μg/ml) and thereafter until week 32 p.p., the weekly mean concentrations ranged between 10 and 28 μg/ml. Toward the end of lactation, approximately during the 33rd week, the concentrations began to increase and were reaching about 3.2-fold higher values in week 44 (107 ± 19 μg/ml). SCC were only available in monthly intervals and could thus not be directly related to the weekly lactoferrin recordings. When classifying the individual goats according to the median of their SCC values obtained during midlactation, the goats with SCC medians >430,000 had higher lactoferrin milk concentrations during this time than the ones with SCC below this threshold (P < 0.05). In addition, sampling week and parity significantly affected the lactoferrin concentration (P < 0.05 and P < 0.01, respectively). Comparing SCC and lactoferrin, both parameters are significantly affected by various physiological factors. Further studies are needed to clarify if the relationship between Lf and bacterial counts is closer compared to the relationship between SCC and bacterial counts.     

Lactation performance of transgenic goats expressing recombinant human butyryl-cholinesterase in the milk

The production of recombinant proteins in the milk of transgenic animals has attracted significant interest in the last decade, as a valuable alternative for the production of recombinant proteins that cannot be or are inefficiently produced using conventional systems based on microorganisms or animal cells. Several recombinant proteins of pharmaceutical and biomedical interest have been successfully expressed in high quantities (g/l) in the milk of transgenic animals. However, this productivity may be associated with a compromised mammary physiology resulting, among other things, from the extraordinary demand placed on the mammary secretory cells. In this study we evaluated the lactation performance of a herd of 50 transgenic goats expressing recombinant human butyryl-cholinesterase (rBChE) in the milk. Our findings indicate that high expression levels of rBChE (range 1–5 g/l) are produced in these animals at the expense of an impaired lactation performance. The key features characterizing these transgenic performances were the decreased milk production, the reduced milk fat content which was associated with an apparent disruption in the lipid secretory mechanism at the mammary epithelium level, and a highly increased presence of leukocytes in milk which is not associated with mammary infection. Despite of having a compromised lactation performance, the amount of rBChE produced per transgenic goat represents several orders of magnitude more than the amount of rBChE present in the blood of hundreds of human donors, the only other available source of rBChE for pharmaceutical and biodefense applications. As a result, this development constitutes another successful example in the application of transgenic animal technology.     

Energetics and litter size variation in domestic dog Canis familiaris breeds of two sizes

We measured resting metabolic rate (RMR), daily energy expenditure (DEE) and metabolisable energy intake (MEI) in two breeds of dog during peak lactation to test whether litter size differences were a likely consequence of allometric variation in energetics. RMR of Labrador retrievers (30 kg, n=12) and miniature Schnauzers (6 kg, n=4) averaged 3437 and 1062 kJ/day, respectively. DEE of Labradors (n=6) and Schnauzers (n=4) averaged 9808 and 2619 kJ/day, respectively. MEI of Labradors (n=12) was 22448 kJ/day and of Schnauzers (n=7) was 5382 kJ/day. DEE of Labrador pups (2.13 kg, n=19) was 974 kJ/day and Schnauzers (0.89 kg, n=7) were 490 kJ/day. Although Labradors had higher MEIs than Schnauzers during peak lactation, there was no difference in mass-specific energy expenditure between the two breeds. Hence, it is unlikely that litter size variation is a likely consequence of differences in maternal energy expenditure. Individual offspring were relatively more costly for mothers of the smaller breed to produce. Therefore, litter size variations were consistent with the expectation that smaller offspring should be more costly for mothers, but not that smaller mothers should per se invest more resources in reproduction.     

Secretion of whey acidic protein and cystatin is down regulated at mid-lactation in the red kangaroo (Macropus rufus)

Milk collected from the red kangaroo (Macropus rufus) between day 100 and 260 of lactation showed major changes in milk composition at around day 200 of lactation, the time at which the pouch young begins to temporarily exit the pouch and eat herbage. The carbohydrate content of milk declined abruptly at this time and although there was only a small increase in total protein content, SDS PAGE analysis of milk revealed asynchrony in the secretory pattern of individual proteins. The levels of alpha-lactalbumin, beta-lactoglobulin, serum albumin and transferrin remain unchanged during lactation. In contrast, the protease inhibitor cystatin, and the putative protease inhibitor whey acidic protein (WAP) first appeared in milk at elevated concentrations after approximately 150 days of lactation and then ceased to be secreted at approximately 200 days. In addition, a major whey protein, late lactation protein, was first detected in milk around the time whey acidic protein and cystatin cease to be secreted and was present at least until day 260 of lactation. The co-ordinated, but asynchronous secretion of putative protease inhibitors in milk may have several roles during lactation including tissue remodelling in the mammary gland and protecting specific proteins in milk required for physiological development of the dependent young.     

Energetics of offspring production: a comparison of a marsupial (Monodelphis domestica) and a eutherian (Mesocricetus auratus)

This study compares the energetic cost of reproduction during gestation and lactation of a eutherian, the golden hamster (Mesocricetus auratus), and a similar-sized (60–120 g) marsupial, the gray short-tailed opossum (Monodelphis domestica). Food consumption was monitored in 20 reproductively active (RA) opossums and 16 RA hamsters from conception to weaning and at equivalent intervals in 19 non-reproductive (NR) opossums and 21 NR hamsters, all maintained within their zone of thermoneutrality (30 °C). Total energy assimilated from conception to weaning [opossums: 1261.3 ± 28.0 Kcal (1 Kcal = 4.1868 J) and hamsters: 1647.5 ± 60.6 Kcal] was positively correlated with litter size and mass per young in both species. Maternal mass-specific assimilated energy was significantly greater in hamsters than in opossums during gestation (P < 0.001), but not during lactation or from conception to weaning (P > 0.05). Efficiency of offspring production (energy stored in young/incremental energy in RA females) was higher in hamsters than in opossums and, in both species, it was higher during lactation than in gestation. The energetic cost of reproduction (per young per day) was higher in hamsters than in opossums. The marsupial mode of reproduction, as seen in opossums, yields young at lower cost but requires a longer reproductive period than is the case for a similar-sized eutherian. Accepted: 8 September 1998