Effects of prostaglandins on the ovine corpus luteum: blood flow, secretion of progesterone and morphology.

Abstract

Intra-uterine administration of prostaglandin F,o-tham salt (PGF,a) 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 (P<0.01). In an attempt to separate a direct effect of PG on the luteal cell from the effects on ovarian blood flow, analogs of PGF2o, ICI-79939 and ICI-81008, having 10 times more and 50 times less smooth muscle stimulating activity than PGF2O, 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, P<0.01) and ICI-81008 (r = 0.50, P<0.05) In corpora lutea removed from ewes 0, 6, 12, 24 and 48 h after administration of PGF, o there was a decrease in percentage of the total volume of the corpus luteum occupied by endothelial cells (P<0.001), red blood cells (P<0.01) and lumens of capillaries (P<0.05) with time. There was an increase in cellular debris in the extra-cellular space (P<0.O1) and within capillaries (P<0.05) after injection of PGF2o. 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, cnrpora lutea removed from ewes 6 h after injection of PGF, o 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 PGF2o 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 PGF2o to ewes were similar to the changes described for granulosa-lutein cells. The data obtained from these experiments indicate that administration of PGF, a to ewes reduced blood flow to the ovary with a corpus luteum and reduced secretion of progesterone. Morphological studies suggested that PGF2o affected the vascular component of the corpus luteum.