Thesis (Ph.D.) - Cairo University - Faculty of Veterinary Medicine - Department of Histology and Cytology

It has been found that pregnancy in rabbit enhances atresia of large follicles. Also in the presence of CL the follicles grew faster to reach more rapidly the size at which atresia start. During early and mid- pregnancy the small follicles were increased. The rate of primary follicle formation is faster than the secondary follicle formation. In first half of pregnancy the number of large follicles was declined due to inhibition of small follicle growth by the effect of progesterone, or due to increased atresia of the pre-antral follicles. In late-حregnancy, the growing and large antral follicles were increased. The interstitial gland cells became bulky. Early in postpartum there was a decrease in the small follicles with an increase in the large antral follicles. The rabbit rely on their corpora lutea as the major source of progesterone during pregnancy. The CL is formed of one type of large lutein cells rich in abundant lipid droplets. When a CL was present, follicular growth was inhibited due to secretion of progesterone. Lutinization process started just after ovulation by the transformation of the postovulatory follicles into CL. The granulosa cells differentiated to form large lutein cells together with a highly complicated network of blood capillaries. The peak of luteal activity was reached at the 14th day of pregnancy where the CL became fully developed and reached its maximum size. It remained morphologically active until the end of pregnancy, and then declined gradually as pregnancy advanced. Clear signs of luteolysis were found. The CL was significantly decreased in size than before. Programmed cell death or apoptosis, and not macrophages is responsible for CL cell regression

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