Follicular 3 beta-hydroxysteroid dehydrogenase and cytochromes P450 17 alpha-hydroxylase and aromatase messenger ribonucleic acids in cattle undergoing superovulation

In this study, we tested the hypothesis that there is altered abundance of transcripts of genes coding for the enzymes cytochrome P450 17 alpha-hydroxylase (P450(17 alpha)), cytochrome P450 aromatase (P450(arom)), and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) in follicles of cattle hyperstimulated with eCG compared to FSH. Treatments were initiated on Day 10 of the cycle, and all cows received prostaglandin (PG) on Day 12. In experiment 1, blood samples were taken to determine plasma progesterone and estradiol concentrations during ovarian stimulation. In experiment 2, both ovaries were removed from stimulated cows by colpotomy before (n = 4 cows/treatment) and at 12 (n = 3/treatment) and 24 h (n 3/treatment) after PG injection, and from nonstimulated controls (n = 4) 72 h after PG. The preovulatory follicle from nonstimulated heifers, and all follicles greater than 3 mm in diameter from superovulated heifers, were isolated and classified as small (3-5 mm), medium (6-9 mm), or large (> 9 mm). Steady-state levels of RNA for 3 beta-HSD, P450(17 alpha), and P450(arom) genes were determined by Northern analysis in the individual follicles. In experiment 1, stimulation with eCG significantly (p < 0.01) increased plasma progesterone concentrations compared to FSH-stimulated and nonstimulated controls, and increased (p < 0.05) plasma estradiol concentrations compared to FSH-stimulated controls. Stimulation with FSH did not alter progesterone concentrations, but significantly increased plasma estradiol concentrations compared to those of controls. In experiment 2, the number of large follicles increased significantly with time (p < 0.01), but there were no differences between eCG and FSH treatments in size distribution of follicles (p > 0.05). Relative abundance of P450(17 alpha), message (per 20 micrograms RNA) was significantly higher in large and small follicles (p < 0.05) in eCG-treated compared to FSH-treated heifers after PG injection.