Atresia in follicles grown after ovulation in the pig: measurement of increased apoptosis in granulosa cells and reduced follicular fluid estradiol-17 beta.
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The incidence of atresia in the first group of follicles grown after ovulation was investigated in the pig. At slaughter, 113 follicles 3-6 mm in diameter were dissected from the ovaries of four pregnant pigs per day on Days 5, 6, and 7 after the onset of estrus. Granulosa cells were isolated from each follicle. The percentage of granulosa cells containing sub-diploid amounts of DNA (%Ao cells), a measure of apoptosis, was determined for each follicle by DNA fluorescence flow cytometry of propidium iodide (PI) stained nuclei of ethanol-fixed cells. Granulosa cell DNA condition was used to classify follicles. Follicles with > or = 10% Ao cells (n = 33) were designated biochemically atretic (BA), and follicles with < 10% Ao cells (n = 80) were designated biochemically healthy (BH). Internucleosomal cleavage, also indicative of apoptosis, was determined by autoradiographic analysis of [32P]-3'-end-labeled DNA from granulosa cells. Densitometric analysis showed that optical density of [32P]-3'-end-labeled DNA fragments in the 0.18-20-kb size range was correlated with the %Ao cells (R > or = 0.90, N = 22, p < 0.001). The incidence of pigs with BA follicles was 2 of 4, 3 of 4, and 4 of 4 on Days 5, 6, and 7, respectively. The %BA follicles per pig (mean +/- SEM) increased (p < or = 0.01) between Days 5 and 7; values were 6.2 +/- 3.6, 28.1 +/- 13.5, and 50.0 +/- 7.1, respectively, on Days 5, 6, and 7.(ABSTRACT TRUNCATED AT 250 WORDS)