A scanning electron microscopic study of the luteo-follicular complex. II. Events leading to ovulation

Ovulation involves a series of timed hormonal biochemical and morphological events. This study demonstrated by scanning electron microscopy (SEM) the process of ovulation. Ovaries from 35 mice 15 rats and 12 rabbits were studied. The animals had not received exogenous hormone to induce ovulation. After removal at the proper phase of the estrous cycles ovaries were prepared for SEM and for parallel transmission electron microscopy (TEM). Details of methods used were given. By SEM preovulatory follicles were seen as blisterlike structures protruding from the ovarian surface. Numerous "papillae" were observed around some of these forming a "flowerlike bouquet." The superficial epithelium of the ovaries with cuboidal or polyhedral cells having numerous microvilli was present only about the base of the preovulatory follicles. The apices of preovulatory follicles had areas of flattened cells with few short microvilli. Some showed degeneration and desquamation revealing an amorphous connective tissue stroma beneath. Many spherical or ovoidal blebs were seen on the surface at the aspices of preovulatory follicles. By TEM amorphous fluidlike material was seen in the connective tissue of the tunica albuginea the intercellular spaces under basal lamina and in vacuoles in the cytoplasm of many superficial cells. At ovulation areas at the apex of the follicle ruptured. Large amounts of fluid (liquor folliculi) and tissue debris were then present obscuring images of ovulated oocytes. The zona pellucida was a dense amorphous membrane cov ered with fine granules similar to those seen in the cells of the corona radiata. It seems that the increase in fluids (edema) may be a major cause of the progressive changes of tissues occurring in the apical zone of the preovulatory follicley Vascular changes in the perifollicular ar eas may also occur. Ovulation seems to be a gradual process in which the oocyte immersed in the gellike material of the liquor folliculi escapes from the ruptured surface of the ovary. The nature of any expulsive force is controversial. Also the composition and function of the granular materials seen on the surface of corna cells and zona pellu cida remain obscure. The text are 9 plates with explanations of appearances.