Scanning Electron Microscopy of the Surface Epithelium of the Pig Ovary

Some structural features of the surface epithelium of the pig ovary were examined by scanning electron microscopy. There were no vesicular follicles visible on the ovarian surface of the infantile pig (13 days of age), and their surface epithelium consisted of polygonal cells that had numerous short microvilli and a few isolated ciliumlike processes. In the prepuberal (6 to 7 months of age) or postpuberal pig ovary, the surface epithelium was observed at a low magnification as a continuous cellular layer. In these pigs the surface epithelium over the vesicular: follicle, generally consisted of polygonal cells covered with numerous microvilli. The presence of a small number of long cilium-like processes among the microvilli was also noted on the epithelial cells covering the follicle. The size of surface epithelial cells over a large follicle appeared to be somewhat larger than that of those over a small or a medium-sized follicle. The surface over the ovulated follicle (corpus luteum) differed in structure from the preovulated follicle. Epithelial cells covering the apical region of the ovulated follicle were scarcely observed at early metestrus, although whenever such existed, the cells possessed fewer microvilli than did the cells over the pre-ovulated follicle. In general, the cell borders at the apical region of the ovulated follicle were indistinguishable at metestrus even if cells were observed, but became distinct during diestrus. However, in other regions, the structure of epithelial cells covering. the ovulated follicle appeared to be about the same as. that of those covering the. pre-ovulated follicle. It appears that the morphological features of the surface epithelium of the pig ovary are similar to those of laboratory animals and primates. Jpn. J. Zootech. Sci., 53 (10): 692-698, 1982 The surfaces of mammalian ovaries are covered with a surface epithelium. Scanning electron microscopic observations have been made on the surface epithelium covering ovarian follicles of the mouse1-3), rat1,3-5), hamster5,6), guinea pig1), rabbit1,3-5, 7,8) , monkeys4) and human1,4,9). However, such observations have not been made on farm animals. The morphological changes in the ovarian surface epithelium that occur during and subsequent to ovulation are probably associated with the progressive degeneration of the cells1,2,8,10). The surface epithelium may contribute to the production of proteolytic enzymes which help to disintegrate the follicle apex prior to rupture11). In general, the microvilli on the surface epithelium of organs within the body cavit increase the physiologically active surface area of the cell5). The present scanning electron microscopic study was designed to examine the fine structure of the surface epithelium of the pig ovary. Jpn. J. Zootech. Sci., 53 (10): 692-698 692 1982 Surface Epithelium of the Pig Ovary Materials and Methods Ovaries from 2 infantile (13 days of age), 4 prepuberal (6 to 7 months of age) and 10 postpuberal Landrace pigs were obtained at slaughter. The number, size and conditions of vesicular follicles and corpora lutea visible on the ovarian surface were examined to determine the stages of the estrous cycle12-14). Ovaries were gently washed in 0.1M phosphate buffer, pH 7.2. Then 10 to 20 follicles for each of three size classes (1~2mm,3~5mm, and 6~12mm) and 5 to 10 corpora lutea for each stage of the estrous cycle were dissected from the ovaries. Ovarian surfaces that were not in contact with follicles or corpora lutea were also dissected. The tissues were fixed for 6 to 8 hr at 4°C by immersion in a solution of 2.5% glutaraldehyde in 0.1M phosphate buffer and cut into small blocks with a razor blade. After immersion for 12 to 15 hr in the same buffer, the specimens were post-fixed in 1% osmium tetroxide buffered with 0.1M phosphate (pH 7.2)for 3 hr at 4°C and then dehydrated in a graded series of ethanol. From 100% ethanol the specimens were transferred to iso-amyl acetate. Following serveral changes of iso-amyl acetate they were dried with liquid CO2 by the critical point method. The dried specimens were coated with gold in a JEOL Fine Coat sputtering apparatus and observed with a JEOL JSM-P15 scanning electron microscope.