Immunohistochemical demonstration of FSH and LH in the pituitary of the developing frog, Rana esculenta

The ontogenetic pattern of immunohistochemically detectable FSHβ and LHβ cells was investigated in the pars distalis of the pituitary of the frog, Rana esculenta. The appearance, distribution, and percentage of these cells were examined in tadpoles from soon after hatching to the end of metamorphosis and in juveniles. We used monoclonal antibodies against bullfrog FSHβ and LHβ for single staining, and either mouse anti-bullfrog LHβ + guinea pig anti-rat FSHβ or rabbit polyclonal anti-bullfrog LHβ + mouse monoclonal anti-bullfrog FSHβ for double staining. The first appearance of gonadotropes, immunopositive for FSHβ, was revealed in stage 26 tadpoles. In successive stages of development the percentage of FSHβ- positive cells increased progressively and significantly. The mean percentage of these in the pars distalis cells increased from 0.7% in stage 26 to nearly 10% during the metamorphic climax (stages 31-33). In juveniles, the mean percentage of FSHβ-positive cells increased more than twofold compared to the climax value. The appearance of LHβ-positive cells was first recorded during the climax, and the mean percentage of LHβ-positive cells in juveniles reached levels as high as 30% or more, exceeding the number of FSHβ-positive cells. In climax, all LHβ-positive cells stained with anti- FSHβ as well. In juveniles, however, up to 80% of gonadotropes demonstrated colocalization of FSHβ and LHβ staining. We argue that both gonadotropins may be synthesized in all gonadotropes, and a small number of cells immunoreactive to either of the two gonadotropins may simply indicate that at that particular moment the cell contained detectable amounts of only one form of gonadotropin. These observations are discussed in relation to the possible involvement of hypothalamic influence in the differentiation of gonadotropes of the pituitary.