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 F2 alpha (PGF2 alpha) treatment were compared to control corpora lutea at 60 min after saline treatment. There were decreases (P less than 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 less than 0.05). PGF2 alpha was then compared with prostaglandin F1 alpha (PGF1 alpha), prostaglandin E1 (PGE1), and 17-phenyl-18,19,20-trinor-prostaglandin F2 alpha (17-phenyl-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 PGF1 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphorylation of Myristoylated Alanine-Rich C Kinase Substrate (MARCKS) Protein Is Associated with Bovine Luteal Oxytocin Exocytosis1

“…Administration of PGF 2␣ to cows during the midluteal phase of the cycle causes rapid degranulation of large luteal cells [31], consistent with the increase in systemic concentrations of oxytocin detected after injection of this eicosanoid [15]. These secretory granules in luteal cells exist as a large cluster in a paranuclear position with the size of the cluster often exceeding that of the adjacent nucleus.…”

Chronic regulation of ovarian oxytocin and progesterone release by prostaglandins: opposite effects in bovine granulosa and early luteal cells

“…The synergistic effects of prostaglandins and insulin in granulosa cells presumably, therefore, reflect synergistic effects on oxytocin synthesis. This contrasts to the in-vivo oxytocin-releasing effect of PGF2a which is very rapid and is associated with depletion of luteal oxytocin (Flint & Sheldrick, 1983), implying action via release of oxytocin from a pre-existing secretory granule store (Heath, Weinstein, Merritt et al 1983;Guldenaar et al 1984;Rice, Jenkins & Thorburn, 1986). Several prostaglandins are produced by granulosa and luteal cells (Richards & Bagovich, 1982;Milvae & Hansel, 1983;Rodgers, Mitchell & Simpson, 1988) and levels of PGEs and PGF2a are particularly high in preovulatory follicles (Murdoch, Dailey & Inskeep, 1981) and the early corpus luteum (Milvae & Hansel, 1983).…”

Subcellular fractionation of the porcine corpus luteum: sequestration of progesterone in a unique particulate fraction

“…However, studies correlating changes in luteal pro¬ gesterone secretion with changes in a distinct popu¬ lation of electron-dense single-membrane-bounded granules (200-250 nm diameter) which could be dif¬ ferentiated cytochemically and morphologically from other organelles, such as primary and secondary lysosomes and microperoxisomes (Quirk, Willcox, Parry & Thorburn, 1979;Parry, Willcox & Thorburn, 1980;Paavola & Christensen, 1981), led to the conclusion that progesterone was packaged in these organelles, and that steroid secretion involved exocy tosis of these granules (Gemmell & Stacy, 1979a,b,c;Sawyer, Abel, McClellan et al 1979;Parry et al 1980;Heath, Weinstein, Merritt et al 1983;Fields, Dubois & Fields, 1985). Secretory granules were thought to con¬ tain a carrier protein (Willcox & Thorburn, 1981;Willcox & Alison, 1982; Willcox, 1983) which seques¬ tered progesterone within the granule (Gemmell & Stacy, 1979a;Quirk et al 1979;Sawyer et al 1979).…”

“…Secretory granules were thought to con¬ tain a carrier protein (Willcox & Thorburn, 1981;Willcox & Alison, 1982; Willcox, 1983) which seques¬ tered progesterone within the granule (Gemmell & Stacy, 1979a;Quirk et al 1979;Sawyer et al 1979). Granules originated in the Golgi region of the large luteal cell (Parry et al 1980;Heath et al 1983) and migrated to the paranuclear regions of the cell as they matured, accumulating beneath the perivascular plasma membrane (Abel, McClellan, Verhage & Niswender, 1975). Granules were then exocytosed by fusion of the secretion granule membrane with the luteal cell-surface membrane, with the release of granule contents into the circulation (Gemmell & Stacy, 1919a,b).…”