Milk is synthesized by mammary epithelial cells of lactating mammals. The synthetic capacity of the mammary gland depends largely on the number and efficiency of functional mammary epithelial cells. Structural develop...Milk is synthesized by mammary epithelial cells of lactating mammals. The synthetic capacity of the mammary gland depends largely on the number and efficiency of functional mammary epithelial cells. Structural development of the mammary gland occurs during fetal growth, prepubertal and post-pubertal periods, pregnancy, and lactation under the control of various hormones （particularly estrogen, growth hormone, insulin-like growth factor-I, progesterone, placental lactogen, and prolactin） in a species- and stage-dependent manner. Milk is essential for the growth, development, and health of neonates. Amino acids （AA）, present in both free and peptide-bound forms, are the most abundant organic nutrients in the milk of farm animals. Uptake of AA from the arterial blood of the lactating dam is the ultimate source of proteins （primarily 13-casein and a-lactalbumin） and bioactive nitrogenous metabolites in milk. Results of recent studies indicate extensive catabolism of branched-chain AA （leucine, isoleucine and valine） and arginine to synthesize glutamate, glutamine, alanine, aspartate, asparagine, proline, and polyamines. The formation of polypeptides from AA is regulated not only by hormones （e.g., prolactin, insulin and glucocorticoids） and the rate of blood flow across the lactating mammary gland, but also by concentrations of AA, lipids, glucose, vitamins and minerals in the maternal plasma, as well as the activation of the mechanistic （mammalian） target rapamycin signaling by certain AA （e.g., arginine, branched-chain AA, and glutamine）. Knowledge of AA utilization （including metabolism） by mammary epithelial cells will enhance our fundamental understanding of lactation biology and has important implications for improving the efficiency of livestock production worldwide.展开更多
基金supported by Texas A&M Agri Life Research (H-8200)The Agriculture and Food Research Initiative Competitive Grant from the Animal Growth & Nutrient Utilization Program of the USDA National Institute of Food and Agriculture (2014-67015-21770)+4 种基金National Basic Research Program of China (2012CB126305)National Natural Science Foundation of China (31572412 and 31272450)the 111 Project (B16044)Natural Science Foundation of Hubei Province (2013CFA097 and 2013CFB325)Hubei Hundred Talent program
文摘Milk is synthesized by mammary epithelial cells of lactating mammals. The synthetic capacity of the mammary gland depends largely on the number and efficiency of functional mammary epithelial cells. Structural development of the mammary gland occurs during fetal growth, prepubertal and post-pubertal periods, pregnancy, and lactation under the control of various hormones （particularly estrogen, growth hormone, insulin-like growth factor-I, progesterone, placental lactogen, and prolactin） in a species- and stage-dependent manner. Milk is essential for the growth, development, and health of neonates. Amino acids （AA）, present in both free and peptide-bound forms, are the most abundant organic nutrients in the milk of farm animals. Uptake of AA from the arterial blood of the lactating dam is the ultimate source of proteins （primarily 13-casein and a-lactalbumin） and bioactive nitrogenous metabolites in milk. Results of recent studies indicate extensive catabolism of branched-chain AA （leucine, isoleucine and valine） and arginine to synthesize glutamate, glutamine, alanine, aspartate, asparagine, proline, and polyamines. The formation of polypeptides from AA is regulated not only by hormones （e.g., prolactin, insulin and glucocorticoids） and the rate of blood flow across the lactating mammary gland, but also by concentrations of AA, lipids, glucose, vitamins and minerals in the maternal plasma, as well as the activation of the mechanistic （mammalian） target rapamycin signaling by certain AA （e.g., arginine, branched-chain AA, and glutamine）. Knowledge of AA utilization （including metabolism） by mammary epithelial cells will enhance our fundamental understanding of lactation biology and has important implications for improving the efficiency of livestock production worldwide.
