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Endocrinology, Vol 127, 1186-1193, Copyright © 1990 by Endocrine Society

ARTICLES

The biosynthesis of cholesterol side-chain cleavage cytochrome P-450 in the rabbit corpus luteum depends upon estrogen

PL Keyes, JL Kostyo, DB Hales, SY Chou, CX Constantino and AH Payne
Department of Physiology, University of Michigan, Ann Arbor 48109.

To gain a better understanding of the luteotropic action of estrogen, we have investigated the effect of estrogen on the synthesis of the enzyme, cholesterol side-chain cleavage cytochrome P-450 (P-450scc) in the rabbit corpus luteum. Using an established protocol, rabbits were treated with estradiol, and the estradiol was then withdrawn on day 9 of pseudopregnancy, which caused an 88% fall in serum progesterone within 48 h. In other rabbits, estradiol was replaced at 48 h which stimulated a 6.6-fold increase in serum progesterone concentration within the next 24 h. Luteal tissues were incubated with [35S]methionine and homogenized, and a mitochondrial fraction lysate was obtained. Equal trichloroacetic acid-precipitable radioactivity was taken for immunoprecipitation using a well-characterized polyclonal antiserum against bovine adrenal P-450scc. The immunoisolated proteins were resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and radioactivity was visualized by autofluorography. The results indicate that the rate of synthesis of P-450scc in 48 h- estradiol withdrawn animals was markedly reduced, and by 72 h of withdrawal was barely detectable. When estradiol was reintroduced, the synthesis of P-450scc was increased. Despite the prominent changes in P- 450scc synthesis, immunoblotting revealed only a minimal (approximately 30%) decrease in relative P-450scc content by 72 h after estradiol withdrawal. Analyses of DNA and protein contents of luteal tissues revealed an increase in DNA per mg luteal tissue, a decline in total tissue protein/DNA ratio, but no change in mitochondrial fraction protein/DNA ratio after estrogen withdrawal. The results indicate that de novo synthesis of P-450scc in the corpus luteum is sensitive to estrogen; however, the estrogen-sensitive rate-limiting step(s) for steroidogenesis are at other sites in the steroid biosynthetic pathway.


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J. S. Babischkin, G. J. Pepe, and E. D. Albrecht
Estrogen Regulation of Placental P-450 Cholesterol Side-Chain Cleavage Enzyme Messenger Ribonucleic Acid Levels and Activity During Baboon Pregnancy
Endocrinology, January 1, 1997; 138(1): 452 - 459.
[Abstract] [Full Text] [PDF]


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