STEROIDOGENIC CYTOCHROME-P450 ENZYME MESSENGER RIBONUCLEIC-ACIDS AND FOLLICULAR-FLUID STEROIDS IN INDIVIDUAL FOLLICLES DURING PREOVULATORY MATURATION IN THE PIG

Changes in follicular concentrations of steroidogenic cytochrome P450 enzyme mRNAs were determined during preovulatory maturation. RNA was i solated from 59 individual follicles dissected from 18 pigs during alt renogest-synchronized preovulatory follicular maturation: at Day 1 (pr e-follicular phase), Day 3 (early follicular phase), Day 5 (mid-follic ular phase), and Day 7 (late follicular phase, 24-36 h after the onset of the LH surge). Follicular fluid was aspirated for steroid RIA. RNA was also isolated from pooled granulosa cells, theca tissue, and lute al tissue. RNA was analyzed by Northern and slot-blot procedures using cDNA probes to human aromatase cytochrome P450 (P450(arom)), porcine l7 alpha-hydroxylase cytochrome P450 (P450(17 alpha)), and porcine cho lesterol side-chain cleavage cytochrome P450 (P450(scc)). P450(arom) m RNA was expressed in both granulosa and theca interna cells but was no t detectable in luteal tissue from Day 13 of the estrous cycle. Follic ular P450(arom) mRNA concentration tended to increase between Days 1 a nd 5 and decreased (p less than or equal to 0.05) by 92% between Days 5 and 7. Follicular fluid estradiol-17 beta concentration increased 17 -fold between Days 1 and 5 and then decreased (p less than or equal to 0.05) by 96% between Days 5 and 7. P450(17 alpha) mRNA was present in theca interna but was not detected in granulosa cells or luteal tissu e. Follicular P450(17 alpha) mRNA concentrations did not differ signif icantly among days, but the content per follicle increased (P < 0.05) between Days 1 and 5 and decreased (p < 0.05) between Days 5 and 7. P4 50(scc) mRNA was detected in granulosa cells, theca interna, and lutea l tissue; but its concentration was 4- to 5-fold greater in luteal tha n in follicular tissue. Follicular P450(scc) mRNA concentration increa sed (P less than or equal to 0.05) between Days 3 and 5 and decreased (P less than or equal to 0.05) by 69% between Days 5 and 7. Follicular fluid progesterone concentration increased (p less than or equal to 0 .05) progressively between Days 1 and 7. P450(scc) mRNA concentration in newly formed luteal tissue recovered from one Day 7 pig was 8-fold greater than that in follicles recovered on Day 7. We conclude that ch anges in follicular estradiol-17 beta production could be explained, i n part, by changes in the pattern of P450(arom) mRNA expression, which increased until Day 5 and then decreased after the preovulatory LH su rge. In contrast, progesterone production increased throughout preovul atory maturation in spite of a transient decrease in P450(scc) mRNA co ncentration after the LH surge.