Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 20, 1994
Publication Date: N/A
Interpretive Summary: Reproductive efficiency in the pig is heavily dependent upon the number and fertilizability of follicular oocytes. At any time during development, over 50% of ovarian follicles are undergoing atresia (an apoptotic form of programmed cell death) resulting in the death or abnormal development of their oocytes. Reduction in the incidence of follicular atresia requires more knowledge about causes and biochemical characteristics of follicular atresia. We used DNA fluorescence flow cytometry to develop a new technique to identify atretic follicles and measure apoptosis in follicle cells. A subpopulation of follicle cells with degraded DNA was identified in follicles showing morphological signs of atresia and low levels of estrogen production. We will use these results as a basis for studies on the molecular regulation of follicular growth and atresia in swine. These studies will provide knowledge required better to regulate ovulation rate.
Technical Abstract: Ovaries were recovered at slaughter from 4 pigs each on days 5, 6 and 7 after the onset of estrus (day 0) in pregnant pigs. Granulosa cells from 113 follicles > 3 mm in diameter were fixed in 80% ethanol and stained with propidium iodide (PI) for DNA analysis by flow cytometry. Analysis of DNA fluorescence histograms revealed an apoptotic subpopulation of granulosa cells with reduced PI binding to DNA (the Ao region) below the Go/G1 peak. Follicles were defined biochemically atretic (BA) or healthy (BH), respectively, if they contained > 10 or < 10% Ao granulosa cells. Of 33 follicles determined to be BA, 21 were classified as morphologically atretic. The proportion of BA follicles per pig increased from 6% on day 5 to 28% on day 6 and 50% on day 7. In BA follicles the mean proportion of Ao granulosa cells increased from 15% on day 5 to 30% on day 6 and 42% on day 7 and mean follicular estradiol concentration decreased between day 5 and 7. Androstenedione also decreased (P<.025) between days 5 and 7 in BA follicles while, in contrast, mean progesterone concentration increased. In BH follicles the proportion of Ao granulosa cells remained unchangedbetween day 5 and 7 (mean=3%), but follicular estradiol, androstenedione and progesterone decreased between day 5 and 7. We conclude a) that the increased incidence of atresia among follicles on day 7, characterized by increased granulosa cell apoptosis and decreased estradiol production, represents the end of the first wave of post- ovulatory follicular growth in the pig and b) that estradiol production decreased in BH follicles even though DNA degradation had not begun.