Role of prolactin in nuclear maturation and ovulation in amphibian oocytes

The present study was undertaken to determine the effect of prolactin (Prl) on Bufo arenarum oocyte maturation and ovulation, two characteristic events of the breeding period, the stage of the sexual cycle in which gamete growth is complete. We observed that Prl, at the doses assayed, did not affect nuclear maturation per se. In addition, when follicles were pretreated with Prl and progesterone was later added to the medium as a physiological nuclear maturation inducer, the percentage of germinal vesicle breakdown obtained with the steroid was unaffected by Prl. The analysis of the in vitro ovulation process demonstrated that pituitary homologous homogenate (PHH) produced a dose- and month-dependent stimulating effect. The maximum percentage of ovulated oocytes was obtained from the end of July to October, the period in which oviposition naturally occurs. Prl by itself did not affect the ovulation process, but when both the hormone and PHH were present in the incubation medium, a significant increase in ovulated oocytes was observed. The results suggest that Prl does not participate in oocyte maturation; however, its presence in the incubation medium would increase oocyte sensitivity to the action of the physiological ovulation inducers.