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Title: Reduced nursing frequency during prolonged lactation in the mouse decreases milk production and increases mammary expression of tryptophan hydroxylase 1 (TPH1), but does not accelerate mammary gland remodeling

Author
item HADSELL, D - Children'S Nutrition Research Center (CNRC)
item OLEA, W - Children'S Nutrition Research Center (CNRC)
item TORRES, D - Children'S Nutrition Research Center (CNRC)
item GEORGE, J - Children'S Nutrition Research Center (CNRC)
item COLLIER, R - University Of Arizona

Submitted to: Journal of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 7/7/2008
Publication Date: 7/7/2008
Citation: Hadsell, D.L., Olea, W., Torres, D., George, J., Collier, R.J. 2008. Reduced nursing frequency during prolonged lactation in the mouse decreases milk production and increases mammary expression of tryptophan hydroxylase 1 (TPH1), but does not accelerate mammary gland remodeling [abstract]. Journal of Animal Science. 86(E-Suppl.2):439.

Interpretive Summary:

Technical Abstract: We have observed that lactating mouse dams nursed 4 times per day (4X) maintained lactation, but had lower milk yields by the weigh-suckle-weigh method, than dams nursed ad libitum (AL). Therefore, we hypothesized that decreased nursing frequency would also decrease lactation persistence, increase mammary gland remodeling, and alter the expression of genes linked to milk production (a-lactalbumin), mammary involution (lactoferrin) and mammary secretory cell feedback inhibition (TPH1). To test this hypothesis, milk output, mammary epithelial and adipocyte content, and mammary gland gene expression was measured on days 8, 14, or 28 postpartum in dams (n=5-16/treatment group) that nursed either AL or 4X for up to 3 weeks. Milk yield (1.3+/-0.1 g) was lower on day 14 in 4X than AL, which had similar yield to day 8 of the pretreatment period (2.4+/-0.3 g). On days 14 and 28, milk production in both groups was similar, and both were lower than that observed on day 8. Mammary epithelial content in 4X dams, as determined in cytokeratin 8 stained tissue sections, was higher than AL on day 28 (70+/-2 and 56+/-2%). Alveolar luminal area was greater in 4X than AL on both days 14 (4030+/-201 and 3307+/-207 (mu)m2) and 28 (3293+/-246 and 2010+/-275 (mu)m2). Mammary adipocytes in perilipinstained tissue sections, were larger in AL than 4X on day 28 (374+/-53 and 134+/-5 (mu)m2). Expression of alpha-lactalbumin and lactoferrin genes was greater on day 28 than day 8 postpartum, but not affected by nursing frequency. Expression of the TPH1 gene was higher in 4X than AL on day 14 (4.2+/-0.9 and 1.7+/-.3 fold over day 8), but similar to AL on day 28. These data suggest that reduced nursing frequency decreases milk synthesis through a mechanism involving serotonin biosynthesis, but may also delay the normal mammary gland remodeling that occurs with prolonged lactation.