Immunocytochemical identification of growth hormone (GH) cells in the pituitary of three anuran species using an antiserum against purified bullfrog GH.

An antiserum was prepared against the recently purified bullfrog (bf) growth hormone (GH); it was applied to sections of brain and pituitary of three urodele (Ambystoma, Pleurodeles and Cynops) and three anuran (Xenopus, Bufo vulgaris and B. japonicus) species. No immunostaining was obtained in the urodele pituitary, being consistent with the results of immunoblot analysis of the pituitary homogenate. In the three anuran species, strong immunoreactivity was observed in GH cells that were concentrated in the posterodorsal region of the pars distalis. No GH-like immunoreactivity was detectable in the brain of any of the species. A comparison using adjacent sections stained with anti-bf prolactin (PRL) confirmed the anteroventral localization of PRL cells. Colocalization of GH and PRL was not apparent. These data suggest that the molecular structure of amphibian GHs is considerably different between anurans and urodeles. The antiserum used in the present work shows a high species specificity, recognizing only anuran GHs. In contrast anti-bfPRL labeled PRL cells in all the amphibian species studied in the present work, suggesting that PRLs possess common amino acid sequences recognized by the anti-bfPRL.