Immunohistochemical localization of enkephalin and ACTH-related substances in the pituitary of the lamprey

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Abstract
The distributions of ACTH-, αMSH-, βLPH-, and enkephalin-related substances were determined immunohistochemically in the pituitary of the brook lamprey, Lampetra lamotenii. An antiserum directed against the middle region of ACTH reacted chiefly with cells in the proadenohypophysis. An antiserum specific for αMSH reacted with all of the cells of the meta-adenohypophysis, but did not react with any of the middle ACTH-positive cells in the pro-adenohypophysis. Several antisera which crossreact with both βLPH and β-endorphin did not react with any region of the lamprey pituitary. However, an antiserum directed against γLPH did react with a small population of cells in the meso-adenohypophysis. This reactivity could be blocked following pre-absorption with mouse βLPH but was not blocked by synthetic β-endorphin(1–31). Antisera directed against either met-enkephalin or leuenkephalin reacted with fibers in the anterior neurohypophysis, cells in the pro-adenohypophysis, and all the cells of the meta-adenohypophysis. This crossreactivity could be blocked following pre-absorption with the appropriate enkephalin, but not by pre-absorption with synthetic β-endorphin(1–31) or dynorphin(1–13). In addition, the enkephalin-like reactivity in the adenohypophysis of the lamprey was coincident with middle ACTH-like immunoreactivity in the pro-adenohypophysis and with αMSH-like immunoreactivity in the meta-adenohypophysis. The absence of βLPH/β-endorphin immunoreactivity coincident with ACTH immunoreactivity, and the presence of enkephalin-like material in the adenohypophysis are unique to the lamprey.