Qualitative and quantitative morphological studies of the cells of the membrana granulosa, theca interna and corpus luteum of the bovine ovary

Ovaries from normal adult dairy cows were obtained at all days of the estrous cycle. The largest Graafian follicle and corpus luteum were excised, prepared for light microscopy, examined morphologically, and quantitations of nuclear sizes were made using a planimetric technique. During the 3-4 days before ovulation, membrana granulosa cells ceased growing in size, and their nuclei decreased in size and frequently appeared pyknotic. Theca interna cells during this time formed two populations: large epithelioid cells with round nuclei, that enlarged significantly, and smaller fibroblast-type cells with spindle-shaped nuclei, that did not enlarge. During the 3-4 days after ovulation, the membrana granulosa cells of the ovulatory follicle and their nuclei enlarged significantly and contributed to the "large luteal cell" population of the corpus luteum. The spindle-shaped theca interna cells of the ovulatory follicle assumed rounded shapes and, together with some paraluteal and trabecular luteal cells (both, probably, of theca externa origin), contributed to the "small luteal cell" population of the corpus luteum. The epithelioid theca interna cells of the same follicle dispersed into the ovarian stroma. Eosinophils and mast cells were commonly observed among the theca cells during this time. The observations are interpreted in relation to periestrual ovarian hormone synthesis. It is suggested that the epithelioid theca interna cells during proestrus and estrus may secrete estrogens and that the large luteal cells during diestrus may secrete progesterone.