Prostaglandin synthesis in vitro by ovarian follicles and extrafollicular tissue of the viviparous guppy (Poecilia reticulata) and its regulation
✍ Scribed by Venkatesh, B. ;Tan, C. H. ;Lam, T. J.
- Publisher
- John Wiley and Sons
- Year
- 1992
- Tongue
- English
- Weight
- 939 KB
- Volume
- 262
- Category
- Article
- ISSN
- 0022-104X
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✦ Synopsis
Abstract
Developmental changes in the prostaglandin synthesising potential in vitro of follicles of the viviparous guppy during oocyte growth and gestation were investigated. Basal production of PGE and PGF was low in follicles during oocyte growth, maturation, and early gestation, increased in mid and late gestation, and declined at postparturition. A similar pattern was also observed in the production of these prostaglandins by follicles at different developmental stages in the presence of exogenous arachidonic acid. Extrafollicular (EF) ovarian tissue of the guppy synthesised large amounts of PGE and PGF spontaneously as well as from exogenous arachidonic acid. Late gestation follicles and EF tissue incorporated ^14^C‐arachidonic acid into PGE~2α~, PGF~2α~, 6‐keto‐PGF~1α~, and monohydroxyeicosatetraenoic acids. The ability of mid and late gestation stage follicles to synthesise large amounts of prostaglandins suggests that it may be related to ovulation and parturition. Extrafollicular tissue may also play a role in the induction of ovulation and parturition. Dibutyryl cAMP inhibited prostaglandin production by late gestation follicles and EF tissue in a dose‐dependent manner. Although the physiological significance of the effect of cAMP is not known, it is possible that high levels of cAMP during oocyte maturation may inhibit ovulation of mature oocytes by inhibiting prostaglandin synthesis. Cortisol (25 and 250 ng/ml) inhibited PGE and PGF production by late gestation follicles. Both the doses of cortisol tested also inhibited PGE production by EF tissue. However, only the higher dose was effective in inhibiting PGF production by EF tissue. Ovarian steroids such as estradiol‐17β, testosterone, 17α,20β‐P, and progesterone (5 and 50 ng/ml) had no effect on PGE and PGF production by late gestation follicles and EF tissue. Our earlier studies on serum steroid profile in the guppy have shown that cortisol levels decline at periparturition. It is possible that this decline may remove the block on prostaglandin synthesis, leading to increased synthesis of prostaglandins, which are presumably involved in the induction of ovulation and parturition. © 1992 Wiley‐Liss, Inc.