Hormones in milk: chemical signals to the offspring?
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Animals↗
Biomedical subjects
M C Neville
Publications and source records attributed to M C Neville.
Lipoprotein lipase in human milk: compartmentalization and effect of fasting, insulin, and glucose.
The object of this study was to investigate the effect of maternal metabolic state on the activity of lipoprotein lipase (LPL) in human milk. Although the total LPL activity in milk was not significantly affected by up to three cycles of freezing and thawing, the amount of LPL associated with the cream fraction of the milk increased from an average of less than 10% to about 70% after this treatment. The enzyme was relatively stable when the milk was stored on ice, losing activity at a rate of about 1% per hour. At 37 degrees C degradation was more rapid, about 7% per hour. When LPL activity was measured in samples taken at hourly intervals by breast pump, using oxytocin to achieve a complete letdown at each pumping, activity was found to double from the first to the third pumping. Thereafter the activity was stable under fasting conditions. Hyperglycemic and euglycemic, hyperinsulinemic glucose clamp protocols were used to evaluate the effects of glucose and insulin. Both high plasma glucose and high plasma insulin in the presence of normal glucose significantly increased LPL activity within 4 hours. We conclude that, like adipose, tissue LPL, mammary LPL is regulated by plasma insulin.
Adult↗
Distribution and source of lipoprotein lipase in mouse mammary gland.
During lactation lipoprotein lipase (LPL) is elevated in mammary tissue and depressed in adipose tissue to redirect lipids for incorporation into milk fat. The cellular origin of lipoprotein lipase in mammary tissue is thought to be the mammary epithelial cell which is the predominant cell type noticeable in the lactating gland; however, mammary adipocytes are also present. If lipoprotein lipase is produced by adipocytes in other sites of the body, then the question remains as to why mammary adipocytes have not been shown to produce lipoprotein lipase. In this study we present several lines of evidence that indicate that the mammary adipocyte is a source of LPL in the lactating mammary gland of mice. This evidence includes the absence of extracellular and intracellular lipoprotein lipase activity in two types of primary mammary epithelial cell cultures and a similarity in the changes of lipoprotein lipase activity in genital adipose tissue from nonpregnant mice and lactating mammary tissue to the nutritional state of the animal. Other evidence presented here includes strong localization of lipoprotein lipase protein and messenger RNA by fluorescence immunohistochemistry and in situ hybridization, respectively, to interstitial cells located between epithelial structures. We postulate that these interstitial cells are regressed, lipid-deleted mammary adipocytes.
Adipose Tissue↗
Divalent cation activation of galactosyltransferase in native mammary Golgi vesicles.
Millimolar concentrations of manganese are required for maximal activation of purified galactosyltransferase (lactose synthase, EC 2.4.1.22), the enzyme that catalyzes addition of galactosyl groups to proteins and, in lactose synthesis, to glucose. To examine manganese activation of this enzyme under in vivo conditions, we studied intact, partially purified Golgi membranes from mouse mammary glands. In intact vesicles treated with the divalent cation ionophore, A23187, activation followed Michaelis-Menton kinetics with a Km of 3 microM; maximal activation was achieved below 10 microM manganese. In both detergent-solubilized and leaky vesicles the kinetics of manganese activation were consistent with the presence of two manganese-binding sites with dissociation constants about 40 microM and 20 mM. The difference is consistent with the presence in intact vesicles of an endogenous activator too large to traverse the membrane via A23187; this activator could bind to the low affinity manganese site allowing manganese or another divalent cation such as zinc to activate the enzyme at micromolar concentrations. The Km for UDP-galactose was found to be similar in the vesicular and solubilized preparations at micromolar and millimolar manganese concentrations, respectively, providing additional evidence for this hypothesis.
Animals↗
The physiological basis of milk secretion.
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Animals↗
Studies in human lactation: secretion of zinc, copper, and manganese in human milk.
Zinc, copper, and manganese were measured in milk samples collected longitudinally from 13 highly selected, healthy lactating women. Samples were obtained at least weekly up to 1 mo and then monthly up to 18 mo postpartum or to weaning. Zn concentrations in milk declined throughout lactation from 71.9 +/- 18.3 mumol/L (means +/- SD) at 7 d to 44.3 +/- 10.7 mumol/L at 1 mo and 7.64 +/- 4.59 mumol/L at 12 mo. Cu levels also declined from 9.76 +/- 2.05 mumol/L at 7 d to 3.46 +/- 0.79 mumol/L at 5 mo with little change thereafter. Zn and Cu were not affected by weaning. Mn concentrations declined from 67.4 +/- 23.7 nmol/L at 1 mo to approximately 36 nmol/L by 3 mo and then remained constant to 7 mo when mean levels started to rise. Gradual weaning was associated with large and irregular changes in Mn levels. Total daily outputs in milk averaged 26.0 mumol Zn, 3.9 mumol Cu, and 35 nmol Mn over the first 3 mo postpartum and 13.8 mumol Zn, 2.7 mumol Cu, and 29 nmol Mn over the second 3 mo.
Breast Feeding↗
Milk composition and volume during the onset of lactation in a diabetic mother.
Milk volume and composition were examined in a diabetic mother on days 3-7 postpartum. By day 5 milk volume produced and concentrations of sodium, potassium, chloride, lactose, protein, calcium, magnesium, and citrate were within limits of a reference population. Fat content of the milk was slightly lower. Free fatty acids were 2% of total lipid on day 3 but increased to 23% on days 4-7, suggesting impaired esterification in the mammary gland. Total milk lipoprotein lipase increased approximately fourfold during days 4-5. Other changes were 1) low cholesterol content, only one-fifth of normal milk; 2) decreased medium-chain fatty acids, suggesting impairment of fatty acid synthesis in the mammary gland; 3) increased oleic acid; and 4) high concentrations of polyunsaturated fatty acids, suggesting increased chain elongation. These results suggest that diabetes produces changes in lipid metabolism in the mammary gland that alter the composition of milk produced by the diabetic mother.
Adult↗
Regulation of milk fat synthesis.
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Adipose Tissue↗
Studies in human lactation: milk volumes in lactating women during the onset of lactation and full lactation.
After validation of test-weighing procedures milk volumes produced by 13 multiparous Caucasian women were followed longitudinally through the first year of lactation. All practiced exclusive breast-feeding for at least 5 mo. Milk transfer to the infant was low on days 1 and 2 and increased rapidly to 498 +/- 129 g/d (means +/- SD) on day 5 and then more slowly to 753 +/- 89 g/d during months 3-5. There was a characteristic milk volume for each mother-infant pair that was significantly related neither to milk yield on days 4-6 nor to birth weight. It was, however, strongly related to infant weight at 1 mo, suggesting that infant and/or maternal factors coming into play during the first month of life are strong determinants of subsequent milk transfer to the infant.
Adult↗
Studies in human lactation 3: molybdenum and nickel in human milk during the first month of lactation.
Molybdenum and nickel were measured in 62 and 46 samples, respectively, of human milk collected from 13 women between delivery and 38 d postpartum. Trace elements were analyzed by graphite-furnace atomic absorption spectrophotometry, with standard additions to whole milk without pretreatment. Molybdenum levels (mean +/- SD) fell from 15.0 +/- 6.1 ng/mL on day 1 to an apparently constant level of 1-2 ng/mL by 1 mo. Nickel concentrations did not change with time; the overall mean was 1.2 +/- 0.4 ng/mL. Intakes of the elements by infants were calculated with test-weighing data on the fully breast-fed infants of these same mothers. By 1 mo, the average daily intake of molybdenum was 1.5 micrograms; that of nickel was 0.8 microgram.
Breast Feeding↗
Nutrient intake by breast-fed infants during the first five days after birth.
The intakes of milk and specific nutrients during the first 120 hours after birth were measured in 11 full-term, breast-fed infants. Infants were test weighed at all feeds using an electronic balance, and milk samples were obtained from both breasts one to three times daily. Milk was analyzed for levels of fat, protein, lactose, calcium, sodium, and potassium; energy content was calculated using the Atwater factors. The average (+/- SD) intake of milk in the first 24 hours after birth was 13 +/- 16 g/kg (range, 3 to 32 g/kg), increasing to 98 +/- 47 g/kg (50 to 163 g/kg) and 155 +/- 29 g/kg (110 to 196 g/kg) on days 3 and 5, respectively. Mean daily intakes of energy, lactose, calcium, and potassium were less than 12% of the mean day 5 intake on day 1 and less than 25% of the day 5 intake on day 2. In the first few days after birth, the nutrient intake of the solely breast-fed infant is highly variable and is frequently low.
Breast Feeding↗
Determination of total protein in human milk: comparison of methods.
We evaluated four spectrophotometric methods for suitability in determining total protein in human milk samples. Results were compared with those by an established method for the determination of total nitrogen (micro-Kjeldahl). Values for total protein by all four methods significantly correlated with micro-Kjeldahl. For the biuret assay, Lowry-Peterson assay, Bio-Rad Coomassie Blue assay, and Pierce BCA assay, the correlation coefficients were 0.96, 0.97, 0.89, 0.99, respectively. We also assessed the sensitivity of each assay to several purified human milk proteins. The Pierce BCA assay showed the least difference in values among different types of protein. For this reason, and because it showed the greatest precision (with acceptable constant and proportional error), we recommend the BCA method.
Colorimetry↗
Studies in human lactation: zinc, copper, manganese and chromium in human milk in the first month of lactation.
Zinc, copper, manganese and chromium were measured in a total of 259 samples of human milk from 11 women from day of delivery to 31 days postpartum. Milk intakes by their fully breast-fed infants were calculated from 24-h test-weighing measurements. Zinc was analyzed by flame atomic absorption spectrophotometry, and the other elements by graphite furnace atomic absorption. Mean (+/- SD) concentrations declined from a maximum of 11.5 +/- 4.7 micrograms/ml at 2 days to 2.98 +/- 0.78 micrograms/ml at 28 +/- 3 days. Changes in the other three elements were irregular. The average copper concentration declined from 0.6 +/- 0.12 micrograms/ml on day 5 to 0.41 +/- 0.04 micrograms/ml at 28 days. Manganese levels decreased from a mean of 5.4 +/- 1.6 ng/ml on day 1 to 2.7 +/- 1.6 ng/ml on day 5; from 8 to 28 days there was little change, the overall mean being 3.7 +/- 2.2 ng/ml. The average concentration of chromium over the whole period was 0.27 +/- 0.10 ng/ml. Average daily intakes of the elements, by the infants, over the one month period were: zinc, 2.0 mg; copper, 0.25 mg; manganese, 2.0 micrograms; chromium, 150 ng.
Adult↗
Insensible weight loss in children under one year of age.
A selected group of 12 breast-fed infants were studied for insensible weight loss over the first year life. The method used to determine the insensible weight loss was non-invasive and based on a computerized weighing system. Findings indicate that the insensible weight loss in a one-year-old child reaches 36% of the average insensible weight loss reached in adulthood (360 g/day). Furthermore, the insensible weight loss (g/h/kg) was constant at about 1.9 g per kilogram per hour over the first year of life. Insensible weight loss contains two components, insensible water loss (92%) and metabolic losses (8%).
Body Weight↗
Sodium and potassium distribution in the lactating mouse mammary gland in vivo.
The ratio of intracellular potassium to sodium in the mammary cells of the lactating mouse was compared with the ratio of potassium to sodium in the mouse milk to determine whether the sodium and potassium concentrations in milk are governed by a Donnan equilibrium as postulated earlier (Peaker 1977a, 1978). An efflux technique was used to determine the average intracellular sodium of 23.0 +/- 1.2 mumol/g tissue (+/- S.E. of mean). The intracellular potassium, determined by calculating the amount of potassium contained in both the interstitial and milk spaces and subtracting these values from the total tissue potassium, was 62 +/- 1 mumol/g tissue. The mean intracellular potassium to sodium ratio, calculated from individual efflux experiments, was 2.7 +/- 0.2. The total, interstitial, and milk water spaces were measured by tissue drying, sodium efflux, and lactose efflux, respectively. The average values (+/- S.E. of mean) obtained were 0.700 +/- 0.004 ml/g tissue, 0.150 +/- 0.016 ml/g tissue and 0.064 +/- 0.004 ml/g tissue. Based on these values the intracellular water space was 0.49 +/- 0.02 ml/g tissue. Intracellular concentrations of sodium and potassium calculated from the intracellular amounts of sodium and potassium and intracellular water space were 47 +/- 3 mM and 129 +/- 5 mM, respectively. The concentrations of potassium and sodium in mouse milk were 47 +/- 1 mM and 26 +/- 1 mM. The mean potassium to sodium ratio (+/- S.E. of mean) calculated from individual milk samples was 1.8 +/- 0.1. The milk ratio of potassium to sodium is significantly different (P less than 0.001) from the intracellular water ratio of potassium to sodium. This finding, in a tight epithelium such as the lactating mouse mammary gland, suggests that both sodium and potassium cannot be distributed passively across the apical membrane and an active transport process must exist for one or both of these ions in this membrane.
Animals↗
Amino acids in milk in cystinuria.
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Amino Acids↗
Accuracy of single- and two-feed test weighing in assessing 24 h breast milk production.
The breast milk intake at a single feed (one-feed method) or the mean intake at two feeds (two-feed method) multiplied by the number of feeds per day was compared with the results of test weighing at every feed during a 24 h period. Six subjects were followed longitudinally from days 1-9 and 21-56 postpartum and the data analyzed by linear regression. There was a reasonable relationship between the mean values for milk intake obtained from the one- and two-feed methods and the 24 h test weights between days 3 and 9 of lactation. However, there was no relationship in full lactation (days 21-56). During both time periods, individual values for the one- and two-feed methods were associated with a large unsystematic error. The one- and two-feed methods may be useful only in situations where mean milk intake for a large population is desired and 24 h test weighing is not possible.
Adult↗
Studies on human lactation. I. Within-feed and between-breast variation in selected components of human milk.
Within-feed and between-breast differences in the concentrations of sodium, potassium, chloride, calcium, magnesium, lipid, protein, lactose, glucose, urea nitrogen, creatinine, zinc, and copper were examined in milk samples from 10 women. The average lipid content doubled in the interval from the beginning of the feed to the end. The composition of the aqueous phase of milk, as determined by the major osmotically active constituents, did not vary significantly within the feed. For these components as well as for lipid a small mid-feed sample of milk gave the same mean composition as the pooled, pumped contents of one breast suggesting that such a sample is adequate for determination of milk composition in population studies. Sporadic, inconsistent differences in the composition of the milk from the right and left breasts were observed. It is suggested that mastitis may contribute to these differences. It is recommended that samples routinely be taken from both breasts and analyzed for sodium and chloride to rule out episodes of mastitis or other local phenomena which sporadically alter milk composition.
Adolescent↗