Regulation of ovarian progesterone biosynthesis by androgens and estrogen in the domestic hen
Lee, Hoon Taek
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https://hdl.handle.net/2142/20067
Description
Title
Regulation of ovarian progesterone biosynthesis by androgens and estrogen in the domestic hen
Author(s)
Lee, Hoon Taek
Issue Date
1989
Doctoral Committee Chair(s)
Bahr, Janice M.
Department of Study
Animal Sciences
Discipline
Animal Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Animal Physiology
Agriculture, Animal Culture and Nutrition
Chemistry, Biochemistry
Language
eng
Abstract
The hen lays eggs on successive days and then skips a day. The laying of these eggs, hence ovulation, occurs every 26 hour. The mechanism controlling this unique ovulatory cycle has not been defined. One level of control of this unique cycle resides in the ovary, specifically the ability of the largest follicle (F$\sb1$) to secrete adequate progesterone (P$\sb4$) to induce the LH surge for ovulation. Therefore, this study focused on the regulation of P$\sb4$ synthesis in F$\sb1$ as a critical event prior to ovulation.
Recent studies implicates androgen and estradiol in the regulation of P$\sb4$ synthesis as an intra-ovarian regulation of steroidogenesis. Therefore, to characterize further this mechanism, it was necessary to investigate (1) the inhibitory sites in P$\sb4$ synthetic pathway where androgens and estradiol exert their inhibitory actions, (2) the mechanism of their actions, and (3) a change in these inhibitory effects during follicular maturation. As a result, androgen and estradiol inhibited the conversion of cholesterol to pregnenolone and pregnenolone to P$\sb4$, respectively, and functioned as competitive inhibitors of P450 side-chain cleavage (P450$\sb{\rm scc}$) and 3$\beta$-dehydroxysteroid dehydrogenase. Moreover, Androgen decreased the amount of P450$\sb{\rm scc}$. Androgen and estradiol regulated P$\sb4$ synthesis beyond LH receptor-linked adenylyl cyclase system. With increasing maturity of F$\sb1$, there were no changes in the responsiveness of the granulosa layer to these inhibitory effects.
This study provides new insights into the mechanism by which androgen and estradiol produced by the theca layer regulate primarily production of P$\sb4$ by the granulosa layer by altering the activities and amount of steroidogenic enzymes, beyond LH receptor-linked adenylyl cyclase system, regardless of maturity of F$\sb1$. Therefore, these findings suggest that P$\sb4$ synthesis in granulosa cells is regulated primarily by androgen and estradiol produced by the theca layer. In conclusion, changes in the steroid profile as follicle matures are presumably regulated by paracrine-autocrine regulatory mechanism between the granulosa and theca layers within chicken follicle.
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