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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Livestock Bio-Systems » Research » Publications at this Location » Publication #145402
Title: BIOCHEMICAL ASSESSMENT OF LIMITS TO ESTROGEN SYNTHESIS IN PORCINE FOLLICLES

Author
item CORBIN, C - UNIV CALIFORNIA, DAVIS
item MORAN, F - UNIV CALIFORNIA, DAVIS
item VIDAL, J - UNIV CALIFORNIA, DAVIS
item Ford, Johny
item Wise, Thomas
item MAPES, S - UNIV CALIFORNIA, DAVIS
item NJAR, V - UNIV MARYLAND
item BRODIE, A - UNIV MARYLAND
item CONLEY, ALAN - UNIV CALIFORNIA, DAVIS

Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2003
Publication Date: 8/20/2003
Citation: CORBIN, C.J., MORAN, F.M., VIDAL, J.D., FORD, J.J., WISE, T.H., MAPES, S.M., NJAR, V.C., BRODIE, A.M., CONLEY, A.J. 2003. BIOCHEMICAL ASSESSMENT OF LIMITS TO ESTROGEN SYNTHESIS IN PORCINE FOLLICLES. BIOLOGY OF REPRODUCTION 69(2):390-397.

Interpretive Summary: Studies were conducted to directly evaluate the activity of two critical enzymes within thecal and granulosal cells of porcine, preovulatory, ovarian follicles. The activity of these two enzymes, Cyp17 and aromatase, has been inferred from steroid concentrations in porcine follicular fluid, but this approach is compromised because concentration is the net of synthesis minus metabolism. Cyp17 is rate limiting for production of androgen by thecal cells; whereas aromatase is found within both thecal and granulosal cells and converts androgens to estrogens. Follicles were evaluated at three stages of development; early follicular, late follicular prior to the ovulatory release of gonadotropins, and late follicular after the preovulatory release of gonadotropins. At all three stages of follicular development, activity of Cyp17 greatly exceeded that of aromatase; thus, we conclude that aromatase is rate limiting for production of estrogen by porcine ovarian follicles. These findings will impact the design of subsequent investigations into means to enhance reproduction of female pigs. Estrogens play a critical role in signaling physiological mechanisms associated with sexual behavior, ovarian follicular development and ovulation.

Technical Abstract: Limits to estrogen production by early and late pre-ovulatory porcine follicles was assessed by comparing enzymatic capacities for androgen (17,20-lyase) and estrogen (aromatase) synthesis in theca interna and granulosa, support of enzyme activities by the redox partner proteins [NADPH-cytochrome P450 oxidoreductase (reductase) and cytochrome b5], their tissue-specific expression and regulation. Parameters included follicular fluid (FF) estradiol and progesterone levels, theca and granulosa aromatase and reductase activities, and theca 17,20-lyase activity. Expression of aromatase (P450arom) and 17alpha-hydroxylase/17,20-lyase (P450c17) cytochromes P450, reductase and, for the first time in ovarian tissues, cytochrome b5, were examined by western immunoblot and immunocytochemistry. Theca and granulosa aromatase activities were as much as 100-fold less than theca 17,20-lyase activity, but aromatase was correlated only with the log of FF estradiol. Granulosa reductase activity was twice that of the theca, and cytochrome b5 expression was clearly identified in both the theca and granulosa layers, as was P450arom, but was not highly correlated with either 17,20-lyase or aromatase activities. Reductase expression did not change with stage of follicular development, but cytochrome b5, P450c17 and P450arom were markedly lower in Post-LH tissues. These data indicate that aromatase not 17,20-lyase must limit porcine follicular estradiol synthesis, but this is not reflected acutely in FF steroid concentrations. Neither reductase nor cytochrome b5 appear to regulate P450 activities, but the expression of cytochrome b5 in granulosa, as well as theca, suggests possible alternative functions for this protein in follicular development or function.