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Title: ESTROGEN-DEPENDENT RESPONSES TO THE MAMMARY FAT PAD IN PREPUBERTAL DAIRY HEIFERS

Author
item MEYER, M - CORNELL UNIVERSITY
item Capuco, Anthony
item BOISCLAIR, Y - CORNELL UNIVERSITY
item VAN AMBURGH, M - CORNELL UNIVERISTY

Submitted to: Journal of Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2006
Publication Date: 9/1/2006
Citation: Meyer, M.J., Capuco, A.V., Boisclair, Y.R., Van Amburgh, M.E. 2006. Estrogen-dependent responses to the mammary fat pad in prepubertal dairy heifers. J. Endocrinol. 190(3):819-827.

Interpretive Summary: A study was performed to evaluate regulation of mammary growth by ovarian steroids. Prepubertal heifers were divided into four groups: 1. untreated, 2. treated with estrogen (E), 3. ovariectomized (OVX) to remove the source of endogenous estrogen, 4. ovariectomized and treated with E. Expression of genes that may serve as mediators of estrogen’s effects were evaluated in: 1. the region of the mammary gland where the epithelial ducts are forming, 2. the mammary fat pad that provides the matrix into which the ducts grow and 3. subcutaneous fat. The mammary fat pad was uniquely sensitive to estrogen. In response to estrogen treatment, the mammary fat pad was primed for production of a known enhancer of mammary growth, IGF-I. These data suggest that the mammary FP is a unique tissue that may help coordinate E-mediated mammary development in prepubertal heifers. A more complete understanding of the fat pad’s role in coordinating prepubertal mammary development in the bovine is warranted.

Technical Abstract: The ovary is required for prepubertal mammary development in the bovine. The aim of this study was to compare the effect of estrogen (E) status on the transcript abundance of specific E-responsive genes within the mammary parenchyma (PAR), mammary fat pad (FP) and another fat depot, subcutaneous adipose (SQA). Four treatments were administered to prepubertal Holstein heifers: ovariectomy (OVX), ovariectomy plus exogenous E (OVX+E), intact (INT), and intact plus exogenous E (INT+E). Ovariectomy had little effect on abundance of transcripts for IGF-I or progesterone receptor (PR) in the three tissues. However, it reduced abundance of proliferating cell nuclear antigen (PCNA) mRNA in FP and increased ER' mRNA in SQA. Exogenous E reduced ER' mRNA in PAR and SQA, but abundance of this transcript in FP was unaffected. E-administration elicited marked increases in IGF-I and PR mRNA in both FP and PAR, with the FP being more responsive than PAR. Similarly, E-administration increased PCNA transcripts in PAR and FP, but not in SQA. Although ovariectomy caused less marked changes in transcript abundance than did administration of exogenous E, cell proliferation in the FP appeared responsive to E deprivation, as PCNA expression was reduced in this tissue. Data do not establish a clear role for prepubertal ovarian secretions in regulating transcript abundance of the genes assessed; however, they demonstrate that the FP is highly responsive to exogenous E and responsive to E-deprivation. A role for the FP in coordinating E-mediated mammary epithelial cell proliferation is suggested. The specific means by which ovariectomy retards mammary development in prepubertal heifers remain elusive.