[Effect of prolactin on gonadotropin-induced ovarian estrogen and progesterone production in mouse]

Immature mice (21-23 days old) were injected with 8 IU PMSG to stimulate follicle growth and followed 24 h later by either injection of 8 IU hCG alone or hCG plus 100 micrograms of prolactin (PRL). The animals were killed at 3, 12 and 24 h after hCG treatment. The ovaries and blood samples were collected. Granulosa cells were prepared for incubation. Progesterone and estrogen concentrations in both the serum and the culture medium were determined. The results showed that PRL significantly enhanced hCG-induced mouse serum progesterone content, while serum estrogen concentrations were considerably decreased by the co-injection of PRL. Prolactin was also capable of stimulating gonadotropin-induced progesterone secretion in the cultured GC. However, the aromatase activity induced by FSH and hCG was remarkably inhibited by the presence of PRL. These data suggest that PRL inhibition of hCG-induced ovulation may be due to its interference with the gonadotropin-induced estrogen production by the follicular granulosa cells.