Prostaglandin synthesis and its inhibition by cyclic AMP and forskolin in postpartum follicles of the guppy (Poecilia reticulata).

Prostaglandin synthesis in vitro and its inhibition by dibutyryl cyclic AMP and forskolin were examined in postpartum follicles of the guppy. The follicles were cultured for up to 72h under chemically-defined conditions, and the synthesis of prostaglandins was determined by radioimmunoassay. The results show unequivocally that the ovarian follicles devoid of embryos can synthesize PGE and PGF from both endogenous precursors as well as added arachidonic acid. That this could be inhibited by indomethacin is indicative of active synthesis rather than release of preformed prostaglandins. Dibutyryl cAMP and forskolin also inhibited prostaglandin synthesis in a dose-dependent manner, as did 3-isobutyl-l-methylxanthine. A similar effect was also evident in vitellogenic oocytes surrounded by follicle layers at the yolk-globule stage of development. While the physiological significance of this action of the cyclic nucleotide remains uncertain at this stage, it is hypothesized that it could explain the non-occurrence of ovulation in this viviparous fish soon after final oocyte maturation.