Effects of Prostaglandins on the Ovine Corpus Luteum: Blood Flow, Secretion of Progesterone and Morphology1

Abstract

Intra-uterine administration of prostaglandin F₂α-tham salt (PGF₂α) to ewes on Days 9 or 10 of the estrous cycle was followed by reduced flow of blood to the ovary containing the corpus luteum and reduced levels of progesterone in the systemic circulation. These parameters were highly correlated (P2α, ICI-79939 and ICI-81008, having 10 times more and 50 times less smooth muscle stimulating activity than PGF₂α, respectively, were administered intramuscularly to ewes on Day 10 of the estrous cycle. Levels of progesterone in the systemic circulation and blood flow to the ovary with a corpus luteum decreased to basal levels within 12 h after treatment in both groups of ewes. Ovarian blood flow and systemic progesterone levels were also correlated in ewes receiving ICI-79939 (r = 0.87, P2α there was a decrease in percentage of the total volume of the corpus luteum occupied by endothelial cells (P2α. Percent volume of the corpus luteum occupied by theca-lutein cells, fibroblasts, eosinophils, connective tissue and white blood cells was not affected by this treatment. Ultrastructurally, corpora lutea removed from ewes 6 h after injection of PGF₂α were similar to corpora lutea removed from control ewes. By 12 h, a proliferation of coated vesicles, dense bodies and lipid droplets was observed in granulosa-lutein cells and local areas of cytoplasmic degeneration were visible. By 24 h after treatment with PGF₂α many of the capillaries which were present contained cellular debris, nucleoli in granulosa-lutein cells were rare and granules within the matrix of the mitochondria were numerous. By 48 h, granulosa-lutein cells were extremely shrunken, contained irregular nuclei with condensed chromatin, abundant lipid droplets and swollen mitochondria. Morphological changes occurring in the theca-lutein cells after administration of PGF₂α to ewes were similar to the changes described for granulosa-lutein cells. The data obtained from these experiments indicate that administration of PGF₂α to ewes reduced blood flow to the ovary with a corpus luteum and reduced secretion of progesterone. Morphological studies suggested that PGF₂α affected the vascular component of the corpus luteum.