ALKALINE-PHOSPHATASE ACTIVITY IN THE THECA OF OVARIAN FOLLICLES OF THE HEN THROUGHOUT FOLLICULAR DEVELOPMENT

Within the hen's ovary, the theca tissue of small follicles that have not yet entered the preovulatory hierarchy is a major contributor to o varian steroidogenesis. Relatively little is known about developmental stages in the theca layer within this pool of follicles and of the hi stological properties of this tissue. In pigs and sheep, alkaline phos phatase activity has been identified in the theca of preovulatory foll icles and in theca-derived cells in the corpus luteum. The objectives of this study were to document morphological changes in the theca laye r through pre- and postovulatory follicular development, and to assess alkaline phosphatase activity at these developmental stages. Ovarian tissue containing small white, large white, small yellow, large yellow , and postovulatory follicles (POF) was obtained from mature White Leg horn hens and embedded in either methacrylate for morphological assess ment or paraffin for alkaline phosphatase histochemistry. Alkaline pho sphatase activity was found to be specific for cells of the theca inte rna in preovulatory follicles. Activity was first detectable in very s mall white follicles, the earliest stage in which the theca interna co uld be distinguished from the theca externa, and highest in the yellow yolky follicles. After ovulation, activity decreased to undetectable levels by the POF4 to 5 stages in POF within 4 to 5 d after ovulation. This study has shown that in the domestic hen, alkaline phosphatase a ctivity is present in cells adjacent to the basal lamina of the theca interna of preovulatory follicles and POF up to 4 to 5 d after ovulati on. Identification of the functional significance of this histological reaction will provide new information on ovarian function in the hen.