The physiological destruction of the corpora lutea in the rat is an orderly, choreographed process. Rat corpora lutea regress gradually over a period of several cycles and are capable of a transient resurgence in growth in the case of a subsequent pregnancy. In the hypophysectomized rat it is clear that the corpora lutea remain steroidogenically active, producing predominantly 20a-dihydroprogesterone. While the inflammatory/immune events observed on estrus are associated with rapid physical destruction of the corpora lutea, measured by loss of luteal wet weight and total protein, the protein per milligram of tissue does not change over this interval (experiment 3), suggesting that the composition of the tissue remains stable, even as the tissue undergoes regression. One interpretation of the observations cited above is that the process of luteal regression in the rat involves the targeted deletion of individual cells, perhaps through apoptosis, leaving other cells in a relatively healthy steroidogenic condition. buy cheap antibiotics
An increase in apoptotic cell death in regressing corpora lutea on estrus suggests that apoptosis is one mechanism by which deletion of tissue occurs. Increases in luteal apop-tosis after prolactin administration, or decreases after blockade of prolactin, have been previously reported. It is also possible that macrophages play some role in deletion of luteal tissue, perhaps by phagocytosis of cells or by the killing of cells through secreted products such as ly-sozyme and reactive oxygen intermediates. Activated macrophages also produce cytokines such as tumor necrosis factor a, which is present in corpora lutea at regression and which has been shown to cause cell death in corpora lutea and luteal cells maintained in culture.