Distribution of endothelin 3-like immunoreactivity in gonadotrophs of the bullfrog (Rana catesbeiana) pituitary.

Abstract Immunohistochemical and immunocytochemical techniques were employed to investigate the distribution of endothelin 3 (ET3)-like immunoreactivity in the pituitary of the bullfrog, Rana catesbeiana. ET3-immunoreactive (ET3-IR) cells were scattered all over the pars distalis of the female pituitary; however, only a few ET3-IR cells were observed in the male pituitary. ET3-IR cells were found to correspond to cells immunostained with monoclonal antibodies against the β-subunit of bullfrog LH (fLHβ) or monoclonal antibodies against the β-subunit of bullfrog FSH (fFSHβ) at the light microscopic level. However, we could not find ET3-IR cells which were immunoreactive for other pituitary hormones. So far, all ET3-IR cells showed both fLHβ and fFSHβ immunoreactivity. About 24% of the fLHβ-IR cells and about 33% of the fFSHβ-IR cells showed ET3-like immunoreactivity. Immunoelectron microscopic analysis using colloidal gold revealed the coexistence of ET3-like substance(s) and gonadotropins within the same granules. This study demonstrated the presence of ET3-like peptide(s) in bullfrog gonadotrophs, suggesting the possible participation of ET3 in regulating pituitary function as an autocrine and/or paracrine hormone.