Structural Changes in the Regressing Corpus Luteum of the Rabbit1

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Abstract
The morphological characteristics of regressing rabbit corpora lutea (CL) were investigated by light microscopy and EM following the and of pseudopregnancy and during lactation. The effect of a 2nd ovulation was also examined. Colloidal C was used as a morphological tracer to assist in the identification of phagocytic cells and the detection of vascular changes. No obvious differences at comparable times were seen among the 3 groups of CL, but variations existed among CL in the same ovary. The connective tissue boundary between CL and surrounding interstitial gland cells appeared to disintegrate dnd disappear at the later stages of degeneration, allowing the 2 cell types to intermingle. Differences among steroid cells throughout the same CL were also observed. Some cells showed signs of regression characterized by whorled membranes and an increase in number, size and variability of lipid droplets. In contrast, other cells had abundant Golgi, spherical mitochondria with a dense matrix and lipid droplets of uniform size. The origin of these latter cells remains speculative and may be important in understanding the relationship of ovarian cell types. Macrophages and other connective tissue cells were not prominent during regression indicating that these cells in the rabbit, unlike other species, may not play an important role in luteolysis.