IMMUNOCYTOCHEMICAL LOCALIZATION AND CHARACTERIZATION OF MAMMALIAN THYROTROPIN-LIKE MATERIAL IN THE PITUITARY OF THE AUSTRALIAN LUNGFISH, NEOCERATODUS-FORSTERI

The binding sites of polyclonal antisera raised against the beta-subun it of human thyroid-stimulating hormone (hTSH beta), hTSH, and ovine T SH (oTSH) have been localized in the pituitary gland of the Australian lungfish, Neoceratodus forsteri, using light microscopy. Reactivity t oward anti-TSH antiserum was demonstrated in a slightly elongated and irregularly-shaped distinct cell type forming clusters in the dorso-ce ntral and ventral regions of the distal lobe. Their granules react wit h alcian blue (AB), and with periodic acid-Schiff (PAS), and after AB- PAS-orange G they stain blue or purple. The specificity of the differe nt antisera was established by liquid-phase absorptions and confirmed in positive and negative tissue control systems. Our observations conf irm that dipnoan (Neoceratodus) TSH shares a number of antigenic deter minants with those of mammalian TSH beta and support the concept that mammalian TSH beta, or part of it, was established early in evolution, and that dipnoans (Neoceratodus) as living sarcopterygians may have a n ancestor in common with the early amphibians. The mapping and detail ed description of TSH-like immunoreactive cells may furnish a backgrou nd to facilitate current and future analysis of the ontogeny and time course of TSH production and release in Neoceratodus in relation to di fferent physiological conditions.