Regulation of messenger ribonucleic acid encoding 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase in the ovine corpus luteum

Three experiments were conducted to determine how steady-state levels of mRNA encoding 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) in the ovine corpus luteum vary 1) between the two steroidogenic luteal cell types, 2) during the estrous cycle, and 3) during prostaglandin F(2 alpha) (PGF(2 alpha))-induced luteolysis. In the first experiment, RNA (10 micrograms) was isolated from purified preparations (n = 4) of large or small steroidogenic luteal cells. Large luteal cells contained 42% more (p < 0.05) message for 3 beta-HSD per microgram RNA than did small luteal cells, while the amount of mRNA for tubulin did not differ between the two types of luteal cells. To determine whether luteal levels of mRNA for 3 beta-HSD differ during the estrous cycle, corpora lutea were collected from cycling ewes (n = 3/day) on Days 3, 6, 9, 12, and 15 postestrus. Levels of mRNA for 3 beta-HSD were similar on Days 3, 6, 9, and 12 but were lower (p < 0.05) on Day 15 postestrus, while levels of mRNA for tubulin were unchanged. In the final experiment, ewes were treated on Day 10 postestrus with two injections of PGF(2 alpha) (5 mg each) or saline (control) at a 4-h interval. Corpora lutea were collected from ewes (n = 4/treatment) 1 h or 8 h after the second injection of PGF(2 alpha) or 8 h after the second saline injection. Levels of mRNA for 3 beta-HSD were decreased by > 80% (p < 0.05) at both 1 h and 8 h after the second injection of PGF(2 alpha) compared to levels in controls, while mRNA for tubulin remained constant. Serum levels of progesterone had decreased by only 28% and luteal weight and progesterone content were unchanged 1 h after the second injection of PGF(2 alpha). The rapid decrease in mRNA for 3 beta-HSD suggests that PGF(2 alpha) perhaps decreases the rate of synthesis and probably increases the rate of degradation of this message.