Differential appearance of the subunits of glycoprotein hormones (LH, FSH, and TSH) in the pituitary of bullfrog (Rana catesbeiana) larvae during metamorphosis.

The ontogeny of gonadotrophs and thyrotrophs in the bullfrog pituitary was examined immunohistochemically using monoclonal antibodies against bullfrog lutropin beta-subunit (LH beta), follitropin beta-subunit (FSH beta) and its alpha-subunit, and polyclonal anti-human thyrotropin beta-subunit (TSH beta) serum. Immunoreactive alpha-subunit- and TSH beta-, but not FSH beta- and LH beta-containing cells were observed at embryonic stage 24 (Shumway's classification). Immunoreactive FSH beta cells first appeared at Taylor-Korllos stage V, and immunoreactive LH beta cells at stage X. Throughout metamorphosis, several gonadotrophs containing both FSH and LH were found in the ventrocaudal region, but most gonadotrophs contained only FSH. Immunoreactive alpha-subunit cells were always more frequent than the sum of immunoreactive beta-subunit cells, which was confirmed by quantitative studies using immunohistochemical and RIA techniques.