IMMUNOHISTOCHEMICAL DEMONSTRATION OF FSH AND LH IN THE PITUITARY OF THE DEVELOPING FROG, RANA-ESCULENTA

The ontogenetic pattern of immunohistochemically detectable FSH beta a nd LH beta cells was investigated in the pars distalis of the pituitar y of the frog, Rana esculenta. The appearance, distribution, and perce ntage of these cells were examined in tadpoles from soon after hatchin g to the end of metamorphosis and in juveniles. We used monoclonal ant ibodies against bullfrog FSH beta and LH beta for single staining, and either mouse anti-bullfrog LH beta + guinea pig anti-rat FSH beta or rabbit polyclonal anti-bullfrog LH beta + mouse monoclonal anti-bullfr og FSH beta for double staining. The first appearance of gonadotropes, immunopositive for FSH beta, was revealed in stage 26 tadpoles. In su ccessive stages of development the percentage of FSH beta-positive cel ls increased progressively and significantly. The mean percentage of t hese in the pars distalis cells increased from 0.7% in stage 26 to nea rly 10% during the metamorphic climax (stages 31-33). In juveniles, th e mean percentage of FSH beta-positive cells increased more than twofo ld compared to the climax value. The appearance of LH beta-positive ce lls was first recorded during the climax, and the mean percentage of L H beta-positive cells in juveniles reached levels as high as 30% or mo re, exceeding the number of FSH beta-positive cells. In climax, all LH beta-positive cells stained with anti-FSH beta as well. In juveniles, however, up to 80% of gonadotropes demonstrated colocalization of FSH beta and LH beta staining. We argue that both gonadotropins may be sy nthesized in all gonadotropes, and a small number of cells immunoreact ive to either of the two gonadotropins may simply indicate that at tha t 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 differentiat ion of gonadotropes of the pituitary. (C) 1996 Academic Press, Inc.