DIFFERENTIAL-EFFECTS OF INDOMETHACIN ON THE SHEEP OVARY - PROSTAGLANDIN BIOSYNTHESIS, INTRACELLULAR CALCIUM, APOPTOSIS, AND OVULATION

Cells of the apical wall of the dominant follicle and contiguous ovari an surface epithelium become apoptotic with the approach of ovulation in the sheep. It was hypothesized that indomethacin, an established in hibitor of prostaglandin biosynthesis and ovulation, would protect api cal ovarian cells from programmed death. The anovulatory potencies of two systemic doses of indomethacin (200 and 800 mg) were tested in gon adotropin-stimulated ewes. A complete blockade of ovulation occurred a t the higher dose of indomethacin. Ovulation was not inhibited by 200 mg indomethacin. Both doses of drug suppressed follicular prostaglandi n production below pregonadotropin levels. Immunofluorescence detectio n of digoxigenin end-labeled (fragmented) DNA was used as a marker of apoptosis among ovarian surface epithelial and granulosa cells recover ed from the apical hemisphere of preovulatory ovine follicles. Cellula r DNA fragmentation was averted in animals given 800 mg indomethacin, whereas apoptosis ensued after 200 mg. A sustained increase in cytosol ic calcium is generally a prerequisite to apoptotic DNA fragmentation and cell death. Indeed, intracellular calcium, detected by fluorescenc e of fura-2, was elevated in ovarian cells of animals destined to ovul ate (controls, 200 mg indomethacin) in comparison to (safeguarded) cel ls of anovulatory ewes (800 mg indomethacin). These observations provi de circumstantial evidence that apical ovarian cell degeneration by ca lcium-mediated apoptosis is a determinant of follicular instability an d rupture, but that these events are unrelated to the gonadotropin-ind uced rise in prostanoid production characteristic of preovulatory foll icles.