Negative calcium balance during lactation in rural Mexican women.

Background: Additional calcium is required during lactation, and several calcium regulatory factors are involved in calcium balance. In lactating rural women who have marginal nutrition and consume a high-fiber diet, negative calcium balance may be expected.

Objective: We evaluated calcium balance and its association with potential calcium regulatory factors in lactating, rural Mexican women who had marginal nutrition and consumed a high-fiber diet.

Induction of expression of branched-chain aminotransferase and alpha-keto acid dehydrogenase in rat tissues during lactation.

This study was designed to determine the effect of lactation and weaning on the gene expression of branched-chain aminotransaminase (BCAT) and branched-chain alpha-keto acid dehydrogenase (BCKD) in different tissues of the lactating rat. BCAT activity increased in mammary tissue during lactation and was 6-fold higher than in virgin rats. This increase was associated with an increase in protein levels measured by immunoblot analysis, and with an increase in BCAT mitochondrial (BCATm) mRNA concentration.

Negative balance of calcium during lactation in marginally nourished women.

Thirty-three rural Mexican women (age, 18-36y; weight, 50.3+/-3 kg; height, 148.3+/-2 cm) were studied under metabolic balance conditions.

Amino acid intake during lactation and amino acids of plasma and human milk.

The aim of this study was to determine the free amino acid pool in plasma and milk in marginally nourished lactating women. Twenty-eight rural women (age, 23.9+/-5y; weight 50.

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.

Characterization of methylaminoisobutyric acid transport by system A in rat mammary gland.

During lactation, the mammary gland has a large demand for amino acids for the synthesis of milk proteins and fatty acids. Arteriovenous differences in amino acids across the mammary gland show an elevated uptake of small neutral amino acids that are mainly transported via system A. The purpose of this study was to characterize the transport of methylaminoisobutyric acid (MeAIB), an amino acid analog used to model transport by system A in lactating rat mammary gland explants.

[Calcium metabolism in lactating women].

During lactation the main source of the breast-milk calcium seems to be maternal bone. The women who breast-fed, lost bone mineral content, which is recovered once breast-feeding ceased. Breast-milk calcium do not depend on an increase in calcium intake by the lactating mother.

[Free amino acids in plasma and milk of mexican rural lactating women].

Objective: To determine the free amino acid pool in plasma and milk in Mexican rural lactating women.

Methods: Twenty-eight women with an age 24 +/- 5.0 (+/- SD) years, weight 50 +/- 4.

[Lactation performance in rural women with low bioavailability of nutrients from the regular diet].

Metabolizable energy (ME) and apparent nitrogen, fat and energy bioavailability from the habitual diet were measured in a group of lactating women from a Mexican rural community. Food intake was estimated in 40 women, age 24 +/- 3 y 3-5 m postpartum, body weight 48.7 +/- 5.

[Calcium and phosphorus balance in rural lactating women in Mexico].

Objective: To compare the balance of calcium (Ca) and phosphorus (P) between lactation and weaning, and to determine the Ca and P milk production in Mexican rural lactating women.

Methods: Thirty-six women aged 18-36 y, weight 49 +/- 3 kg and height 148 +/- 2 cm, were divided in six groups: four groups of lactation (1st, 3rd, 6th and 12th month) one post-weaning group and one of non pregnant non lactating women. The balance studies were performed collecting duplicate diets, 24 h urine for 3 days, 72 h feces and 24 h milk samples for 2 days.

Regulation of branched-chain amino acid metabolism in the lactating rat.

There is evidence that during lactation, uptake of the essential branched-chain amino acids (BCAA) by mammary glands exceeds their output in milk protein. In this study, we have measured the potential of lactating rats to catabolize BCAA. The activity, relative protein and specific mRNA levels of the first two enzymes in the BCAA catabolic pathway, branched-chain aminotransferase (BCAT) and branched-chain alpha-keto acid dehydrogenase (BCKD), were measured in mammary gland, liver and skeletal muscle obtained from rat dams at peak lactation (12 d), from rat dams 24 h after weaning at peak lactation and from age-matched virgin controls.

Leucine catabolism in mammary tissue, liver and skeletal muscle of dam rat during lactation and weaning.

Background: This study was designed to determine the effect of lactation and weaning on the catabolism of branched-chain amino acids (BCAA).

Methods: Rates of transamination and oxidation of leucine and branched chain alpha-ketoacid dehydrogenase (BCKD) activity were measured in homogenates of mammary gland, skeletal muscle and liver on day 12 of lactation and 24 h after separation of dams from the litter (weaning).

Results: Lactating dams consumed 250% more protein than control rats, extra protein is required for protein synthesis by the mammary gland, the extent to which the excess of amino acids consumed during lactation is utilized or oxidized by different tissues is not known.

Significance of lipid consumption during lactation.

Human milk lipids are the main source of energy to support optimum growth of the breast-fed infant. The content and composition of milk lipids come from three main sources of fatty acids: the diet, mobilization of body fat stores and fatty acid synthesis de novo by the mammary gland. On account of these, the consumption and composition of the lipids from the diet and also the nutritional state, specifically the body fat percentage of the lactating woman, are elements that maintain a close relation with the content and composition of milk lipids which translates into the energy content given to the baby.

Alanine aminotransferase activity in mammary tissue, muscle and liver of dam rat during lactation and weaning.

Transamination reaction is the first step in the catabolism of most of the L-amino acids. Alanine is an important molecule in the inter-organ nitrogen transport, conveying them from muscle to the liver. Amino groups from this amino acid are generally first transferred to alpha-ketoglutarate in the cytosol of liver cells to form glutamate and leaving behind the corresponding alpha-keto acid analog.

Protein requirements of marginally nourished lactating women.

Few experimental data regarding protein requirements of lactating women are available. This study was designed to determine the protein requirement of seven healthy lactating women from a poor Mexican community who were 2-6 mo postpartum and had a mean body mass index of 21.8 +/- 2 kg/m2.

Changes in the composition of mammary tissue, liver and muscle of rat dams during lactation and after weaning.

This investigation was conducted to evaluate the changes in the total content of protein and RNA in liver and muscles of rat dams before and after acute separation from their litters. Groups of 8-12 rats fed ad libitum were killed on the 12th (group L12) and 20th d (group L20) of lactation and on the 1st (group W1) and 7th d (group W7) after weaning. Nonpregnant, nonlactating rats paired for age served as controls.