[Antehypophyseal gonadotropic cells are mediators of the early induction of prolactin cell differentiation by gonadoliberin].

To study lactotrope differentiation in the fetal rat, immunocytochemistry with anti-rat prolactin antiserum was performed on pituitary primordia explanted from 12 to 14 day-old fetuses and cultured in different media until the equivalent of 21 days of gestation. At this time, lactotrope differentiation was observed when culture medium was enriched with fetal calf serum. Estradiol was not involved in lactotrope differentiation. Immunoreactive lactotropes were detected when the synthetic medium was enriched with GnRH (10(-9) M) instead of fetal calf serum. But the induced GnRH lactotrope differentiation was inhibited when an anti-rat LH serum was added to the culture medium. These data suggest that the effect of GnRH on lactotrope differentiation is mediated by the gonadotroph cells.