Tilapia Prolactin Stimulates Estradiol-17-Beta Synthesis Invitro In Vitellogenic Oocytes Of The Guppy Poecilia-Reticulata

Oocytes at different stages of growth were isolated from the guppy and incubated with and without increasing doses (0.01 to 1000 ng/ml) of a tilapia prolactin (tPRL188). Measurement of the estradiol-17β secreted into the medium showed that estrogen synthesis from endogenous precursors was stimulated by tPRL at all stages of oocyte growth. In all cases, the maximal stimulating dose was 1 ng/ml. At this dose, the magnitude of the stimulation in estradiol-17β synthesis was greatest (77%) in oocytes at the beginning of vitellogenesis. These results strongly suggest a role of prolactin in ovarian steroidogenesis of the guppy, and it is possible that this action of prolactin constitutes an additional control mechanism regulating estrogen synthesis in the fish.