help button home button Endocrine Society Endocrinology
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
This Article
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Copyright Permission
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Weiss, M.
Right arrow Articles by Eckstein, B.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Weiss, M.
Right arrow Articles by Eckstein, B.
Right arrowPubmed/NCBI databases
*Substance via MeSH

Endocrinology, Vol 114, 1912-1916, Copyright © 1984 by Endocrine Society

ARTICLES

Periovulatory changes in steroid C17,20-lyase activity in ovaries of immature rats treated with pregnant mare serum gonadotropin

M Weiss and B Eckstein

It has been established that the effect of LH on ovarian steroid formation results initially in a rise of overall steroid production, which 2-4 h later is followed by a decrease in the formation of C19- steroids. To determine the reason for this decrease, the course of 17 alpha-hydroxyprogesterone (17 alpha-OHP) metabolism in immature rat ovaries (10,000 X g supernatant) stimulated to ovulate with pregnant mare serum gonadotropin (PMSG) was investigated. Employing optimal conditions the C17,20-lyase was estimated from the formation of androstenedione from 17 alpha-OHP as substrate. The Michaelis-Menten constant Km was 61 +/- 4 microM and V varied according to the time after PMSG administration. The initial activity at 0 h was 340 pmol min- 1 mg-1 protein. It decreased 48 h after PMSG to 160 pmol, followed by a slight rise at 54 h and followed by a 60% fall at 57 h, at the height of the LH-surge. The activity declined to undetectable levels at 60 and 64 h (8 h before ovulation) and remained undetectable after ovulation at 72 and 96 h after PMSG. The enzymes 5 alpha-reductase and 20 alpha- hydroxysteroid dehydrogenase were estimated from the formed 3 alpha, 17 alpha-dihydroxy-5 alpha-pregnan-20-one and 17 alpha, 20 alpha-dihydroxy- 4-pregn-en-3-one, respectively. In the unstimulated ovary the 5 alpha- reductase was 405 pmol; it decreased to 110 pmol 48 h after PMSG and continued to decrease. The 20 alpha-hydroxysteroid dehydrogenase activity which was undetectable in untreated rats, rose to 330 pmol 60 h after PMSG, 8 h before ovulation. The changes in enzyme activities when tracer amounts of [3H] 17 alpha-OHP were used agreed with the pattern of kinetic studies. From these incubations eight metabolites were isolated, one of them, 5 alpha-pregnane-3 alpha,17 alpha, 20 alpha- trioi, has not been previously identified. It is concluded that the decrease in C17,20-lyase activity limit the formation of C19-steroids in preovulatory follicles shortly before ovulation.


This article has been cited by other articles:


Home page
 EndocrinologyHome page
T. Ronen-Fuhrmann, R. Timberg, S. R. King, K. H. Hales, D. B. Hales, D. M. Stocco, and J. Orly
Spatio-Temporal Expression Patterns of Steroidogenic Acute Regulatory Protein (StAR) During Follicular Development in the Rat Ovary
Endocrinology, January 1, 1998; 139(1): 303 - 315.
[Abstract] [Full Text] [PDF]


HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Endocrinology Endocrine Reviews J. Clin. End. & Metab.
Molecular Endocrinology Recent Prog. Horm. Res. All Endocrine Journals
Copyright © 1984 by The Endocrine Society