OVARIAN FOLLICULAR STEROIDOGENIC ACUTE REGULATORY PROTEIN, LOW-DENSITY-LIPOPROTEIN RECEPTOR, AND CYTOCHROME-P450 SIDE-CHAIN CLEAVAGE MESSENGER RIBONUCLEIC-ACIDS IN CATTLE UNDERGOING SUPEROVULATION

Ovarian hyperstimulation with eCG in cattle results in increased plasm a estradiol and progesterone concentrations, whereas hyperstimulation with FSH increases only estradiol concentrations, This study tested th e hypothesis that eCG, compared to FSH, increases mRNA abundance for s teroidogenic acute regulatory protein (StAR), low-density lipoprotein receptor (LDL-R), and/or cytochrome P450 cholesterol side-chain cleava ge (P450(scc)), the main elements of the progesterone biosynthetic pat hway, Heifers were stimulated with eCG (n = 10) or commercial FSH (n = 10), and ovaries were removed by colpotomy the day before and at 12 a nd 24 h after luteolysis was induced with prostaglandin (PG) F-2 alpha . RNA was extracted from individual follicles, and relative abundance of StAR, LDL-R, and P450(scc) mRNA was assessed by slot blots. In ovar ies of abattoir origin, StAR mRNA was detected in all follicles and wa s present in the theca but not the granulosa cell layer, as shown by N orthern blotting. Levels of StAR mRNA increased 2-fold (p < 0.05) afte r PGF(2 alpha) injection in small (< 6 mm) follicles from eCG-treated but not from FSH-treated animals. After PGF(2 alpha) injection, StAR m RNA levels were 2- to 3-fold higher (p < 0.01) in large (> 9 mm) and m edium (6-9 mm) follicles in eCG- compared with FSH-treated heifers. In contrast, P450(scc) and LDL-R mRNA levels did not consistently differ according to treatments, We show that StAR is expressed in the theca cells of bovine follicles and that stimulation with eCG increases foll icular accumulation of StAR mRNA in comparison to stimulation with FSH .