Effects of neurohypophyseal and adenohypophyseal hormones, steroids, eicosanoids, and extrafollicular tissue on ovulation in vitro of guppy (Poecilia reticulata) embryos

Abstract

In the viviparous guppy, oocyte maturation is followed by intrafollicular fertilization and gestation. The fully developed embryos are ovulated at term just prior to parturition. Various agents were tested in vitro for their effects on ovulation of embryos in isolated follicles of the guppy. Arachidonic acid (10 and 100 μM), PGE2, PGF2α, and 6-keto-PGF1α (0.1 μg/ml) induced ovulation, while PGE1, 15-keto-PGF2α, leukotriene B4, 5-, 12-, and 15-HETEs (0.01 to 0.1 μg/ml), cortisol, 11-deoxycortisol (25 and 250 ng/ml), estradiol-17β, testosterone, 17α,20β-P, progesterone (5 and 50 ng/ml), isotocin, vasotocin (0.02 to 2 μg/ml), and guppy pituitary extract (one and two glands per fish) did not. Extrafollicular (EF) ovarian tissue cocultured with isolated follicles induced ovulation, and the medium levels of PGE and PGF in such incubations were higher than those in the control. Indomethacin, the cyclooxygenase inhibitor, did not inhibit ovulation induced by arachidonic acid and EF tissue, although it inhibited PGE and PGF production. NDGA, the lipoxygenase inhibitor, did not inhibit ovulation induced by arachidonic acid or EF tissue. A combination of eicosanoids synthesized by follicles and EF tissue may be involved in the induction of ovulation. Dibutyryl cAMP inhibited ovulation induced by PGE2, PGF2α, 6-keto-PGF1α, and EF tissue suggesting that a low level of cAMP may be associated with ovulation in the guppy. © 1992.