Porcine Fetal Ovary Tissue Changes And Immunohistochemical Localization Of Nitric Oxide Synthase During Oogenesis

Mammalian ovary undergoes a series of histological changes during the oogenesis, which is an important physiological event.Such event includes ovarigenesis,gonadal cord formation,germ cell proliferation,differentiation and apoptosis,and primordial follicle formation,development and atresia.The studies on the event helpes understand the reproductive process,such as sex differentiation and oogenesis.As a livestock species and a research model,pig has been widely used in medical research.Recognition of porcine ovarigenesis was of the great importance in livestock reproduction and human reproductive clinics.Nitric oxide(NO) plays an important role in mammalian reproductive activities.It's speculated that NO probably involves in oogenesis since it participates in spermatogenesis.The related studies could provide a theoretical basis for controlling reproductive behavior and treating reproductive diseases.It could also have important indications for reproductive health maintenance and medical clinical application of human being.Nitri oxide synthase(NOS) is the only way to produce NO physiologically. Therefore,the study of NOS localization may provide the clue of NO and its function.The present study was undertaken to investigate the tissue structure change of porcine fetal ovary/gonad at 33rd,40th,47th,54th,61st day of gestation by hematoxylin and eosin(HE) staining.Based on this experiment,the localization of endothelial NOS(eNOS) and inducible NOS(iNOS) were examined by immunohistochemistry.The results could provide a basis for the further study of NO functions in oogensis and oocyte apoptosis, and its mechanism.The results of HE staining showed that①Porcine gonads of 33rd day of gestation had obvious sex differentiation.In male gonad,the albuginea and testis cords were observed.In female gonad,in contrast,individually egg cells,or cell cysts with two to three eggs,which surrounded by the spindle-shaped stromal cells,were distributed under the surface epithelium.②synplasma-like cell groups occurred in ovary at 40th day of gestation.Cord-like structure disrupted in medulla.Some of those cells were at leptotene or pre-leptotene stage.③In the fetal ovary at 47th day of gestation,some small cell groups were observed between the boundary of cortex and medulla.Medullary cords were broken into fragments to be island-like cell groups or primordial follicle.④In the fetal ovary at 54th day of gestation,syncytium-like cell group appeared in middle cortex,and primordial follicles appeared in deep cortex and primordial follicles appeared in deep cortex.In medulla,island-like cell group reduced and follicles degenerated.⑤In the fetal ovary at 61 st day of gestation,considerable syncytium-like cell groups occurred in middle cortex and primordial follicles occurred in deep cortex.In medulla,some primordial follicles with single enclosed oocytes were observed.The results of immunohistochemical detection showed that①The eNOS was immunoreactive in the cytoplasm of surface epithelium,oogonium,oocytes,necrotic oogonium and oocytes,as well as in the vascular endothelial cells.The eNOS immunoreactivity was weak in the ovaries at 33rd day of gestation,but stronger at 47th days.The eNOS expression was intense,especially in the cytoplasm of degenerated oogonium and nucleus pyknosis oocytes.②The iNOS was immunoreactive in the nucleus of surface epithelium,oogonium,oocytes,necrotic oogonium and ooeytes.The iNOS expression was intense especially in degenerated oogonium and nucleus pyknosis oocytes.This study systematically investigated the histological change of fetal ovarian tissue from 33rd to 61st day of gestation when the gonads differentiated and primordial follicle formed.By dectecting the distribution of eNOS and iNOS,it's found that both eNOS and iNOS were widely expressed in the surface epithelium,oogonium,oocytes,and necrotic oogonium and oocytes.From 33rd to 61st day of gestation,the expression of eNOS and iNOS increase.This is the first time to find the NOS existence in fetal pig ovary.Taking all of the findings into consideration,we presume that NO play a role in ovarian development during oogenesis.