Effects of Prostaglandins on the Bovine Corpus Luteum: Granules, Lipid Inclusions and Progesterone Secretion

Abstract

Corpora lutea collected at 15, 30 and 60 min after prostaglandin [PG] F2.alpha. (PGF2.alpha.) treatment were compared to control corpora lutea at 60 min after saline tratment. There were decreases (P < 0.05) in the relative percentages of cytoplasm occupied by granules in large luteal cells (LLC) by 30 min and in small luteal cells (SLC) by 60 min. Differences were not observed among the groups for lipid inclusions. Luteal progesterone was decreased at all post-PGF2.alpha. treatment times when compared to 60 min controls (P < 0.05). PGF2.alpha. was then compared with PGF1.alpha., PGE1 and 17-phenyl-18,19,20-trinor-PGF2.alpha. in 60 min trials with plasma progesterone and luteinizing hormone (LH) determined every 5 min. LH was not affected by these treatments. Like PGF2.alpha., 17-phenyl-PGF2.alpha. induced a greater loss of granules from LLC then SLC. 17-phenyl-PGF2.alpha. also induced an increase in the lipid content of LLC. Treatments with PGF2.alpha. and 17-phenyl-PGF2.alpha. were associated with decreased concentrations of luteal progesterone but PGE1.alpha. and PGE1 were without effect on this variable. In contrast to PGF1.alpha., PGE1 increased both luteal progesterone and the area occupied by cytoplasmic granules. The latter effect was greater in LLC than SLC. Changes in the cytoplasmic granule population may be correlated with luteal progesterone storage and release. Degranulation could be specific for luteolytic prostaglandins. LLC apparently are more sensitive than SLC to the effects of luteolytic prostaglandins and PGE1. Changes in lipid inclusions may be secondary effects of luteolytic prostaglandins.