Immunochemical Identification of Thyrotropes and Gonadotropes in the Pars Distalis and Pars Tuberalis of the Toad (Bufo boreas) with Reference to Ontogenic Changes

Abstract

Morphologically distinct secretory cells in the pituitary pars distalis and pars tuberalis of larval and adult toads (Bufo boreas) immunoreact with antiserum to the beta subunit of human thyroid-stimulating hormone (hTSHβ). The single type of secretory cell in the pars tuberalis has sparse secretion granules uniformly smaller than those of similarly immunoreactive cells in the pars distalis. Thyrotropin immunoactivity appears in pars tuberalis and pars distalis before gonadotropin immunoreactivity during early development. Antisera which distinguish gonadotropes (stained with human and sea turtle LHβ) and thyrotropes (stained with human TSHβ) as separate cell types in the pars distalis of the adult toad immunoreact with the same single type of cell in the pars distalis of the tadpole up through metamorphosis, suggesting the existence of a single pluripotent, glycoprotein-producing precursor cell early in development. Gonadotropin antisera do not react with the pars tuberalis in tadpoles or adults.