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

The distributions of ACTH-, alpha MSH-, beta LPH-, 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 pro-adenohypophysis. An antiserum specific for alpha MSH 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 beta LPH and beta-endorphin did not react with any region of the lamprey pituitary. However, an antiserum directed against gamma LPH did react with a small population of cells in the meso-adenohypophysis. This reactivity could be blocked following pre-absorption with mouse beta LPH but was not blocked by synthetic beta-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 beta-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 alpha MSH-like immunoreactivity in the meta-adenohypophysis. The absence of beta LPH/beta-endorphin immunoreactivity coincident with ACTH immunoreactivity, and the presence of enkephalin-like material in the adenohypophysis are unique to the lamprey.