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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 #132800

Title: REGULATION OF MICROSOMAL P450, REDOX PARTNER PROTEINS AND STEROIDOGENESIS IN THE DEVELOPING TESTES OF THE NEONATAL PIG

Author
item MORAN, F - UNIV CALIFORNIA, DAVIS
item Ford, Johny
item CORBIN, C - UNIV CALIFORNIA, DAVIS
item MAPES, S - UNIV CALIFORNIA, DAVIS
item NJAR, V - UNIV MARYLAND SCH MED
item BRODIE, A - UNIV MARYLAND SCH MED
item CONLEY, ALAN - UNIV CALIFORNIA, DAVIS

Submitted to: Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2002
Publication Date: 9/20/2002
Citation: MORAN, F.M., FORD, J.J., CORBIN, C.J., MAPES, S.M., NJAR, V.C., BRODIE, A.M., CONLEY, A.J. REGULATION OF MICROSOMAL P450, REDOX PARTNER PROTEINS AND STEROIDOGENESIS IN THE DEVELOPING TESTES OF THE NEONATAL PIG. ENDOCRINOLOGY. 143(9):3361-3369. 2002.

Interpretive Summary: Secretion of steroid hormones in boars increases abruptly during the first week of life as a result of increased secretion of pituitary gonadotrophic hormones. Changes within the testicles of key enzymes that regulate steroid hormone synthesis have not been investigated. The purpose of the current study was to monitor the concentration of these enzymes during the first 24 days of postnatal testicular development. Additional boars were treated with an antagonist of luteinizing hormone releasing hormone to suppress pituitary gonadotropin secretion. Concentrations of the final rate-limiting enzyme for androgen synthesis, 17-20-lyase, increased with testicular size during the first 7 days after birth and remained at this concentration through day 24. Treatment with the antagonist significantly reduced testicular growth and plasma testosterone concentration but had only a modest effect on 17-20-lyase activity. From these findings we conclude that pituitary gonadotrophins stimulate testicular growth and that the reduction in testosterone secretion results primarily from the lack of testicular growth rather than from a dramatic reduction in 17-20-lyase concentration. Scientists who design subsequent studies relating to porcine testicular steroidogenesis will use these findings. This information is needed to develop technology to use boars for meat production. For such technology, testicular steroid synthesis must remain high enough to stimulate growth and feed efficiency but low enough to limit synthesis of androgens responsible for boar odor in meat.

Technical Abstract: Testicular growth and plasma androgen concentrations increase markedly in the first weeks of neonatal life of pigs. The regulation of steroidogenesis through this period was examined by measuring total microsomal cytochromes P450 (P450), 17alpha-hydroxylase/17,20-lyase P450 (P450c17) and aromatase P450 (p450arom) enzyme activities, and the redox partner proteins NADPH-cytochrome P450 reductase (reductase) and cytochrome b5 in testicular microsomes. Testes were collected from 1 to 24 days of age, and testicular development was suppressed by a gonadotropin releasing hormone (GnRH) antagonist in some animals from day 1 to 14. Both 17/20-lyase and aromatase activities increased from day 1 to 7 but not thereafter, and 17-20-lyase activity was always at least 200-fold higher than aromatase activity. Reductase decreased in the first week, then increased to day 24. No changes were seen in cytochrome b5 expression. GnRH antagonist treatment suppressed plasma LH, testosterone and testes growth to day 14. Activities of 17,20-lyase and aromatase in testicular microsomes were reduced by 20% and 50%, respectively. Total microsomal P450 concentration was reduced by 50% on day 7 but there was no effect of treatment on reductase or cytochrome b5 expression. These data support the hypothesis that the rise in neonatal testicular androgen secretion is more likely due to gonadotropin-stimulated gonadal growth, rather than specific P450c17 expression. Neither P450c17 or P450arom can account for the decline in total microsomal P450. Reductase and cytochrome b5 expression appears to be constitutive but reductase levels saturate both P450c17 and P450arom.