Occurrence of a Contractile Tissue in the Theca externa of Atretic Follicles in the Mouse Ovary

Abstract

In mature mouse ovaries, smooth muscle cells (SMC) are as a rule concentrated in the perifollicular stroma of developing follicles but are also present in different ovarian regions. In growing antral follicles SMC form a conspicuous investment (‘capsule’) of concentric layers of stretched and elongated elements located in the zones of the theca externa. On the contrary, in antral follicles reaching approximately the same growth phase but with clear signs of atresia, the contractile capsule of the follicles has an irregular outline due to an apparent dislocation and shortening of SMC. The ultrastructural findings show that in atretic follicles the majority of the cells forming this capsule possess the cytological characteristics of SMC fixed in contraction. The occurrence of compressed SMC in the wall of atretic follicles suggests that some relationship exists between follicle contraction and the atretic process. In the case of the follicle at ovulation, it may be suggested that the activation of such perifollicular contractile tissue, even if incapable of producing alone the dehiscence of the follicle, may nevertheless be capable of squeezing the follicular wall. Then, if other factors do not simultaneously occur to cause a normal ovulatory processs, the contraction of this tissue, instead of assisting in the rupture of the follicle, may favor its collapse and subsequent involution during atresia.

Genes invoked in the ovarian transition to menopause

“…Our results indicate significantly reduced level of desmin mainly in the perifollicular stroma in old ovaries. Lower desmin content would ultimately result in reduced cellular contractility (8,9) leading to reduced follicle contraction and changes in the atretic process (1). The ovarian architectural aging response may be characterized by stromal remodeling concurrent with loss of cortical follicular units and the accumulation of autofluorescent inclusions.…”

Expression of the Giant Protein AHNAK (Desmoyokin) in Muscle and Lining Epithelial Cells

“…In the ovary, theca cells showed strong plasma membrane AHNAK immunoreactivity ( Figure 2E). Theca cells, which are important for steroid secretion, also have muscle characteristics (Motta and Familiari 1981;Self et al 1988). At ovulation, these cells by their contraction may be capable of squeezing the follicular wall or may favor follicle collapse and subsequent involution during atresia.…”

The fate of thecal smooth muscle cells in postovulatory hamster follicles

“…After luteolysis and regression of the CL, most thecal cells degenerate, while those that remain may assist in the reorganization of the ovarian connective tissue. In a recent study demonstrating SMC in the theca externa of atretic follicles, Motta and Familiari (1981) suggested that SMC may function to compact the degenerating follicle. We believe that this suggestion may be extended to include compaction of ruptured follicles and regressing CL as well.…”

“…Some argue that they are not involved in ovulation (Espey, 1978;1980), whereas other studies suggest that the contraction of SMC occurs prior to rupture of the follicle and is an important part of the normal ovulatory sequence (Martin and Talbot, 1981a,b;Talbot, 1983;Talbot and Chacon, 1982;Owman et al, 1979). It has also been suggested that SMC are involved in collapse of the follicle after rupture and its compaction into a corpus luteum (Fumagalli et al, 1971;Kapinus and Rukosuev, 1976;Amenta et al, 1979;Motta and Familiari, 1981). Before testing this suggestion, it is necessary to determine if SMC persist in the thecal wall during the transition of follicles into corpora lutea (CL).…”