Changes in the size distribution of steroidogenic and non-steroidogenic bovine luteal cells during the oestrus cycle

The aim of this study was to investigate the size distribution of steroidogenic and non-steroidogenic luteal cells throughout the oestrus cycle. Twelve corpora lutea collected from different stages of the oestrus cycle were used. Corpora lutea collected from nonpregnant cows were dissociated into single-cell suspensions by enzyme treatments. Cells were stained for 3b-hydroxysteroid dehydrogenase (3b-HSD) activity, a marker for steroidogenic cells. The sizes of 3b-HSD positive (steroidogenic) and negative cells (nonsteroidogenic) were measured with an ocular micrometer. Very small cells (<10 µm) stained negative for 3b-HSD activity were presumed to be primarily endothelial cells, fibroblast and blood cells. The other cells were presumed to be luteal cells covering a wide spectrum of size ranging from 10 to 40 µm in diameter. 3b-HSD positive cells smaller than 10 µm were not observed, and cells larger than 25 µm were rare. The cells obtained from early and late stages of the luteal phase contained more non-steroidogenic cells than the cells obtained from the mid-luteal phase. However, the cells derived from early luteal stage contained more small cells (10-22 µm) than the cells obtained from the rest of the cycle. There were significant differences (p<0.001) in both 3b-HSD positive and 3b-HSD negative cell sizes during the oestrus cycle. This study indicates that the size distributions of both steroidogenic and non-steroidogenic luteal cells change as the age of the corpus luteum increases