Biosynthesis of estradiol-17β in the ovarian follicles of the red seabream Pagrus major during vitellogenesis

K.Ohta, S. Yamaguchi, A. Yamaguchi, K. Okuzawa, K. Gen, H. Kagawa, M. Matsuyama-2002

Fisheries Research, 68(3): 680-687

Abstract:

The red seabream Pagrus major is a useful experimental fish for studying the endocrine control of oogenesis in teleosts. This study investigated the steroidogenic pathway for estradiol-17β  (E2) biosynthesis in the ovarian follicles of red seabream. Intact follicles were isolated during vitellogenesis and incubated in vitro with different radiolabeled steroid precursors. When 17-hydroxyprogesterone (17-P), dehydroepiandrosterone (DHEA), or androstenedione (AD) were used as precursors, both testosterone (T) and estrone (E1) were synthesized by follicles, leading to estradiol-17β  (E2) production. Serum steroid levels measured by enzyme-linked immunosorbent assay showed that T, E1, and E2 were present in the circulation at levels ranging from 1 ng/mL to 2 ng/mL throughout the day during the spawning season. In vitro conversion of E1 into E2, however, was 15.8-fold greater than T conversion into E2, suggesting that E2 is synthesized mainly via E1 rather than T. The results showed that E2 was synthesized from pregnenolone via 17-hydroxypregnenolone, DHEA, AD, and E1. Thus, the study demonstrated the complete steroidogenic E2 synthesis pathway in the ovarian follicles of red seabream, and revealed that E1 is the major precursor of E2.

(Department of Animal and Marine Bioresources Science, Faculty of Bioresource and Bioenvironmental Sciences, Kyushu University, Fukuoka, Fukuoka 812-8581, Japan, Tel: 81-92-642-2887. Fax: 81-92-642-2888. Email of M. Matsuyama: rinya_m@agr.kyushu-u.ac.jp)

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