This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.HYPOTHESISHypotheses: H1: Physiologic increases in prolactin and oxytocin induced by complete emptying of the breast using a breast pump will increase mRNA of alpha-lactalbumen more than frequent small pulses of breast emptying.
SPECIFIC AIMS :This protocol will attempt to determine if timing of collection in relation to emptying the breast will affect the mRNA content in milk fat globules (MFG) and to determine the relationship of changes in this mRNA concentrations and the plasma concentrations of prolacting and oxytocin.BACKGROUND AND SIGNIFICANCE:Breast milk is the ideal food for newborn infants and infants who are breast fed have a lower incidence of gastroenteritis, otitis media and a number of allergic conditions (Work Group on Breastfeeding). The American Academy of Pediatrics recommends that infant be fed breast milk for the first 6 mondhs of life and partially fed breast milk for up to 1 year (American Academy of Pediatrics Policy). A number of women struggle with breast feeding and less than 25% of those who attempt it are successful for longer than 1 month. It is assumed that lactose production is a primary regulator of human milk production since it is the primary osmotic agent in milk (Mephan 1987). As opposed to milk proteins and fat, the lactose concentration in milk water is constant from the initiation of a breast-feeding until the end, but is species specific (Davies et al 1983). Over the past several years, we have demonstrated using stable isotope tracers of glucose that 50 to 60% of lactose is derived from maternal plasma glucose but that up to 40 to 50% of lactose in human milk is derived from a process of de novo synthesis of lactose within the mammary epithelium (Sunehag et al 2002, Sunehag et al 2003). The proportion of lactose derived from hexoneogenesis is affected by fasting but not rhGH treatment despite the fact that rhGH increased milk production by 30% (Kaplan et al). The mechanism(s) by which hexoneogenesis and lactose synthesis are controlled is not known in humans. The fat component in human milk appears as a milk fat globule (MFG) (Patton et al 1988, Huston et al 1990). Since MFG are produced by an apocrine mechanism, each is surrounded by mammary apical cell membrane which encloses a large lipid droplet and a crescent of mammary epithelial cell cytosol. We believe that if we are able to understand the mechanisms responsible for milk production from a substrate, hormone and molecular basis that we might be in a better position to positively impact the numbers of women who can successfully breast feed their infants.PRELIMINARY STUDIES/PROGRESS REPORTWe have recently demonstrated that we can isolate and quantitate by RT-PCR a number of mRNA species from the milk fat globule in human milk, including a-lactalbumen which is thought to be a key co-factor increasing the activity of galactosyl transferase, a key enzyme in the production of lactose (Stacey et al 1995). The development of this technique we hope will permit us the opportunity to study in vivo regulation of hormonal regulation of transcription and translation of a number of potentially regularoty proteins in the mammary epithelial cell of the human breast. Nipple stimulation as a result of infant suckling or the use of a breast pump triggers a nipple-pituitary reflex resulting in the secretion of both oxytocin and prolactin (Cos 1996). From our initial studies we observed a significant variation of a-lactalbumin mRNA in the milk samples that we have obtained but that this concentration clearly increase over the first 2-3 days of rhGH administration (unpublished data). We believe that these variations may reflect the fact that we were not sensitive to the potential impace of the timing of the obtaining of milk samples in relationship to the last breast feeding.
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