Involution of the sheep mammary gland

Abstract

Changes in the ovine mammary gland epithelium during initiated involution were studied by light and electron microscopy. Apoptosis of the duct and alveolar epithelial cells was first identified at 2 d after weaning, reached a peak at 4 d and then progressed gradually thereafter. Apoptotic cells were phagocytosed by intraepithelial macrophages and alveolar epithelial cells. Occasional apoptotic epithelial cells were observed in the alveolar and duct lumina. The highly vacuolated cells in the alveolar and duct lumina were confirmed to be macrophages as they were CD45+, MHC class II+. Changes in myoepithelial cells involved shrinkage and extension of cytoplasmic processes into the underlying stroma and no apoptosis was observed. Regression of the blood capillaries was also by apoptosis. The resulting apoptotic bodies were either taken up by adjacent endothelial cells or were shed into the capillary lumen to be phagocytosed later by mural endothelial cells or blood monocytes. The mammary glands were completely involuted by 30 d after weaning. It was concluded that the mammary gland involutes by apoptosis, a process which allows deletion of cells without the loss of the basic architecture and the integrity of the epithelial lining of the gland.

Disrupted secretory activation of the mammary gland after antenatal glucocorticoid treatment in sheep

“…We suggest that the premature stimulation of secretion by the lactocytes was followed by loss of function in the absence of milk removal during pregnancy. Mammary gland involution has been shown to commence within 4 days of cessation of milk removal when lactation is established (Tatarczuch et al 1997. This process, which is triggered by milk stasis (Marti et al 1977), results in rapid reductions in the synthesis of major milk components such as lactose (Neville et al 1991).…”

Leucocyte phenotypes in involuting and fully involuted mammary glandular tissues and secretions of sheep

“…One of the reasons given was that this could be due to the loss of the physical barrier by sloughing of the alveolar epithelium. Our recent studies (Lee et al 1996 ;Tatarczuch et al 1997) excluded this possibility as it was clearly shown that the process of apoptosis enabled the deletion of the alveolar epithelial cells without the loss of the integrity of the epithelial lining of the gland.…”

“…One of the reasons given was that this could be due to the loss of the physical barrier by sloughing of the alveolar epithelium. Our recent studies (Lee et al 1996 ;Tatarczuch et al 1997) excluded this possibility as it was clearly shown that the process of apoptosis enabled the deletion of the alveolar epithelial cells without the loss of the integrity of the epithelial lining of the gland.Our previous studies (Lee et al 1989) showed thatCorrespondence to Dr C. S. Lee, Department of Veterinary Science, The University of Melbourne, 3010, Victoria, Australia. Fax :j61 3 9344 7374 ; e-mail : c.lee!vet.unimelb.edu.au in the mammary gland of both nonpregnant and pregnant sheep, the great majority of the lymphocytes in the ductal and alveolar epithelium were agranulated and that they belong to the CD8 + CD5 V phenotype followed by CD45R + cells and CD5 + CD4 + cells.…”

Effects of continuous lactation and short dry periods on mammary function and animal health

“…Conversely, the mammary gland of nonpregnant dairy cows may undergo extensive remodeling of the lobular-alveolar structure after dry-off, as expected in stage II of involution (Leitner et al, 2007). Forced weaning of sheep at 5 days of lactation induced involution that was complete after 30 days (Tatarczuch et al, 1977). In species that are not pregnant at cessation of milk removal, extensive and rapid Collier, Annen-Dawson and Pezeshki cell loss occurs in the mammary gland, followed by gland remodeling to structural similarity to a virgin gland (Capuco and Akers, 1999;Capuco et al, 2002).…”