Lactose Synthesis

Abstract

This chapter is related to lactose synthesis, its chemistry, regulation, and differences between species, especially in cattle. Lactose synthesis takes place in the Golgi apparatus of mammary epithelial cells (MEC) by the lactose synthase (LS) enzyme complex from two precursors, glucose and UDP-galactose. The enzyme complex is formed by galactosyltransferase, and it is associated with α-lactalbumin. Importantly, the lactose secreted determines the volume of milk produced, due to its osmotic properties. Milk contains 5% lactose and 80% water, percentages that remain constant during lactation in the different mammalian species. The low variation in milk lactose content indicates that lactose synthesis remains constant throughout the period of lactation and that is highly conserved in all mammals. Lactose synthesis is initiated during the first third of the pregnancy, increasing after birth and placenta removal. Different glucose transporters have been involved in mammary glucose uptake, mainly facilitative glucose transporters GLUT1, GLUT8, and GLUT12 and sodium-glucose transporter SGLT1, with more or less participation depending on mammal species.

Breast size in lactating women and the content of macronutrients in human milk

“…The appropriate content of lactose in breast milk affects not only the energy value of breast milk, as human infants satisfy 40% of their caloric requirement from the approximately 70 g/d of lactose they consume in the first 6 months of life (Schaafsma, 2008), but is also of crucial for the development of the central nervous system (Coelho et al, 2015; Varma et al, 1962) and has an impact on infant body composition (Gridneva et al, 2019). Moreover, lactose determines the volume of milk produced due to its osmotic properties (Liu et al, 2013; Villagrán & Mardones, 2020). It draws water into the MECs and thus is positively associated with its volume and negatively associated with the osmolarity of its salts (Fox, 2009; Holt, 1983).…”

Γενετική Μελέτη Ποιοτικών Παραμέτρων Του Πρωτογάλατος Σε Γαλακτοπαραγωγές Αγελάδες

“…Ταυτόχρονα, η συγκέντρωση της προλακτίνης μία εβδομάδα πριν από τον τοκετό είναι χαμηλή και 2 ημέρες πριν από αυτόν αρχίζει να αυξάνεται απότομα . Η σταδιακή μείωση της συγκέντρωσης της προγεστερόνης και η παράλληλη αύξηση της συγκέντρωσης της προλακτίνης (Convey 1974, Delouis 1978) διεγείρει τον σχηματισμό της συνθετάσης της λακτόζης (Brodbeck et al 1967, Klein 2013, Mardones et al 2020) με αποτέλεσμα τη σταδιακή αύξηση της παραγωγής λακτόζης, την οσμωτική προσέλκυση ύδατος και τελικά την αύξηση του όγκου του μαστικού εκκρίματος.…”