Dynamics of nuclear associated granules in bovine luteal cells after treatment in vitro with prostaglandin F2 alpha.

A group of electron-dense granules of 150-300 nm in diameter, with a single limiting membrane, were found adjacent to the nuclei of large (25-50 microns in diameter), but not small (15-22 microns), bovine luteal cells of pregnancy. These granules were quite heterogeneous with respect to size, shape, content, etc. Most granules contained varying amounts of light and dark electron-dense material, and very few contained only light or dark material in their core. These granules occupied 160.4 +/- 7.8 microns3 cytoplasmic volume, which did not significantly decrease until 2 h of incubation without any hormone at 22 or 38 C (P greater than 0.05). Subsequently, however, volume occupancy of these granules decreased to 127.3 +/- 6.4 and 117.6 +/- 8.0 microns3 (P less than 0.05) by 4 and 12 h of incubation, respectively. Incubation of luteal tissue with 10 nM prostaglandin F2 alpha (PGF2 alpha), on the other hand, resulted in a decrease to 124.4 +/- 8.0 microns3 of volume occupancy of granules by 10 min (P less than 0.05). The volume occupancy further decreased to 46.2 +/- 4.8 microns3 by 2 h (P less than 0.01), and then the granules virtually disappeared from luteal cells. While PGF2 alpha decreased volume occupancy of granules similarly at 22 and 38 C, it had no effect at 4 C. PGF2 alpha decreased volume occupancy of granules at 0.01 nM (P less than 0.05), which continued to decrease with increasing PGF2 alpha concentrations, reaching a maximal decrease at 10 nM PGF2 alpha (P less than 0.05). PGE1, hCG, human LH, human PRL, or (Bu)2cAMP had no effect on the granules, suggesting that the PGF2 alpha effect was hormone specific. PGE1 and hCG, which protect corpus luteum from the luteolytic action of PGF2 alpha, could not inhibit degranulation by PGF2 alpha. These results demonstrate that treatment with PGF2 alpha in vitro results in a decrease in volume occupancy of nuclear associated granules in bovine large luteal cells of pregnancy in a time-, temperature-, and concentration-dependent and hormone-specific manner.