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 abundanc e of transcripts of genes coding for the enzymes cytochrome P450 17 al pha-hydroxylase (P45017 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 init iated on Day 10 of the cycle, and all cows received prostaglandin (PG) on Day 12. In experiment 1, blood samples were taken to determine pla sma progesterone and estradiol concentrations during ovarian stimulati on. In experiment 2, both ovaries were removed from stimulated cows by colpotomy before (n = 4 cows/treatment) and at 12 (n = 3/treatment) a nd 24 h (n = 3/treatment) after PC injection, and from nonstimulated c ontrols (n = 4) 72 h after PG. The preovulatory follicle from nonstimu lated heifers, and all follicles greater than 3 mm in diameter from su perovulated heifers, were isolated and classified as small (3-5 mm), m edium (6-9 mm), or large (> 9 mm). Steady-state levels of RNA for 3 be ta-HSD, P450(17 alpha), and P450(aroma) genes were determined by North ern analysis in the individual follicles. In experiment 1, stimulation with eCG significantly (p < 0.01) increased plasma progesterone conce ntrations compared to FSH-stimulated and nonstimulated controls, and i ncreased (p < 0.05) plasma estradiol concentrations compared to FSH-st imulated controls. Stimulation with FSH did not alter progesterone con centrations, but significantly increased plasma estradiol concentratio ns compared to those of controls. In experiment 2, the number of large follicles increased significantly with time (p < 0.01), but there wer e no differences between eCG and FSH treatments in size distribution o f follicles (p > 0.05). Relative abundance of P450(17 alpha) message ( per 20 mu g RNA) was significantly higher in large and small follicles (p < 0.05) in eCG-treated compared to FSH-treated heifers after PG in jection. Analysis within this period revealed significant treatment ef fects at 12 h but not 24 h after PC injection. The bovine P450(arom) c DNA hybridized to 3 transcripts: a 6.5-kilobase (kb) polyadenylated tr anscript, and non-poly-adenylated messages of 3.4 and 1.8 kilobases (k b), all of which hybridized with an oligonucleotide probe specific for the heme-binding region. In medium and small follicles, the 6.5-kb an d 3.4-kb transcripts were present in similar quantities, and the 1.8-k b transcript was 25% less abundant. In large follicles recovered after luteolysis, the 3.4- and 1.8-kb transcripts were 3-to 4-fold more abu ndant in eCG-treated compared with FSH-treated and nonstimulated anima ls (p < 0.05). There were no significant differences between eCG and F SH treatments on steady-state 3 beta-HSD mRNA levels. Levels of 3 beta -HSD and P450(17 alpha) mRNA in large follicles in hyperstimulated hei fers were not different from those in preovulatory follicles in nonsti mulated cows. We conclude that hyperstimulation with eCG results in gr eater stimulation of follicular P450(17 alpha) message abundance compa red to hyperstimulation with FSH, and that this may contribute to incr eased follicular estradiol secretion.