Bovine ovary : morphologic and biochemical kinetics
The studies presented in this thesis objectively quantitated the morphological characteristics, ultrastructural features and distribution of follistatin in the wall of dominant and subordinate ovarian follicles of cattle. Ultrasound image attributes of the follicle wall and antrum, and steroid hormone content in the follicular fluid of the dominant and subordinate follicles were analyzed. The dominant and subordinate follicles were obtained during the growing, early and late static, and regressing phases of Wave 1, pre-selection period of Wave 2, and after onset of estrus from the ovulatory Wave. The effects of active immunization against follistatin on follicular development, FSH concentration and superovulatory response in cattle were studied and correlations between ultrasound image attributes, and morphological and functional characteristics of the bovine corpus luteum were investigated. Changes in the morphology, ultrastructure and the distribution of follistatin in the follicle wall, steroid content of the follicular fluid and echotexture attributes of the follicle wall and antrum were all temporally related to the status of the dominant and subordinate bovine ovarian follicles as determined by wave emergence and diameter profiles of individual follicles. At the time of loss of functional dominance, the late-static dominant follicle of Wave 1 exhibited loss of its ability to produce estradiol and there was a decrease in thickness of the follicle wall, an increase in the number of degenerating granulosa cells, a decrease in the amount of smooth and rough endoplasmic reticulum and follistatin in granulosa cells, and major changes in cellular and vascular components of the theca interna. Changes in the echotexture attributes of the CL and ovarian follicles were reflective of their structural and functional characteristics, indicating that a computer-assisted image analysis technique could be developed into a robust non-invasive diagnostic and prognostic tool to determine the functional status of ovarian structures. Follistatin was distributed in the granulosa layer of healthy follicles and in the CL at diesvus. Active immunization against follistatin caused subordinate follicles to grow longer, but no effect on circulating FSH levels could be detected. The results suggested that effects of follistatin on follicular dynamics are not mediated through changes in pituitary secretion of FSH.