STEADY-STATE CONCENTRATIONS OF MESSENGER-RIBONUCLEIC-ACID ENCODING CYTOCHROME-P450 SIDE-CHAIN CLEAVAGE AND 3-BETA-HYDROXYSTEROID DEHYDROGENASE DELTA-5,DELTA-4 ISOMERASE IN OVINE CORPORA-LUTEA DURING THE ESTROUS-CYCLE

The objective of these experiments was to determine the pattern of mRN A expression for cytochrome P450 side-chain cleavage (P450(scc)) and 3 beta-hydroxysteroid dehydrogenase/Delta(5),Delta(4) isomerase (3 beta -HSD) during luteinization of the follicle and in ovine luteal tissue on Days 3, 6, 9, 12, and 15 of the estrous cycle. Mean concentration o f mRNA for P450(scc) was not different in follicles collected 4 or 24 h after the onset of estrus but increased (p < 0.05) 3-fold by 48 h (c orpus hemorrhagicum). With the methods used, mRM1 for SP-HSD was not d etected until after ovulation and formation of the corpus hemorrhagicu m (48 h after onset of estrus). In luteal tissue, mean concentration o f mRNA for P450(scc) increased from Days 3 to 3 (P < 0.05) and had dec reased (p < 0.05) by Day 15. Mean concentration of mRNA for P450(scc) was higher (P < 0.05) in small luteal cells on Day 3 than on Day 15, w ith values on Days 6 and 12 being intermediate. In large luteal cells, mean concentrations of P450(scc) mRNA increased (p < 0.05) between Da ys 6 and 12 and then decreased (P < 0.05) on Day 15. Mean concentratio n of mRNA for 3 beta-HSD was not different (P = 0.33) in luteal tissue on any day examined. In small luteal cells, mean concentrations of mR NA for 3 beta-HSD decreased between Days 6 and 15 (p < 0.05) while in large luteal cells, mean concentrations decreased (p < 0.05) between D ays 12 and 15. In summary, up-regulation of mRNA for P450(scc) and 3 b eta-HSD occurred after ovulation. In the CL, concentrations of mRNA fo r P450(scc) increased from Days 3 to 9 and then decreased again by Day 15. In contrast, concentrations of mRNA for 3 beta-HSD did not change during the estrous cycle. Large luteal cells had higher concentration s of mRNA for P450(scc) and 3 beta-HSD than small luteal cells on most days of the estrous cycle examined in this experiment.