Effect of α-tocopherol deprivation on the involution of mammary gland in sheep

Abstract

The objective of this study was to investigate the effect of α-tocopherol deprivation on mammary gland involution and apoptosis in sheep. Two groups of four single lamb ewes were used. The control group received 100 mg/d of RRR-α-tocopherol supplementation and the experimental group received no vitamin E supplementation. After 3 mo of suckling, ewes were dried off, and blood samples from the jugular vein and tissue biopsies from the mammary gland were collected at d 1, 3, 5, and 8 after dry-off. The experimental group had lower plasma concentrations of α-tocopherol (1.8 vs. 4.2 μmol/L), lower glutathione peroxidase activity in erythrocytes, and higher concentration of malondialdehyde in plasma than the control group. Immunohistochemical analysis of tissue samples resulted in marked differences of bcl-2 and bax protein expressions during involution and between groups. The bax expression was decreased by α-tocopherol deprivation at 1, 3, and 5 d, but not at 8 d, while the bcl-2 score was higher only at 8 d (1.5 vs. 0.0 for experimental and control groups, respectively). As a result, the bcl-2 to bax ratios were increased for the experimental group at 1 and 8 d. During involution, apoptotic counts increased (from 0.12 to 4.06%), but no effects were detected in relation to bcl-2 to bax ratio and α-tocopherol. These results indicate that α-tocopherol can control bcl-2 expression, but not apoptosis in cells of the mammary gland during involution.