in the pituitary of the lamprey

Summary. The distributions of ACTH-, aMSH-, flLPH-, and enkephalin-related substances were determined im-munohistochemically in the pituitary of the brook lamprey, Lampetra lamotenii. An antiserum directed against he mid-dle region of ACTH reacted chiefly with cells in the pro-adenohypophysis. An antiserum specific for aMSH 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 flLPH and fl-endorphin did not react with any region of the lamprey pituitary. However, an antiserum di-rected against 7LPH did react with a small population of cells in the meso-adenohypophysis. This reactivity could be blocked following pre-absorption with mouse flLPH but was not blocked by synthetic fl-endorphin(1-31). Antisera directed against either met-enkephalin or leu-enkephalin reacted with fibers in the anterior neurohypoph-ysis, cells in the pro-adenohypophysis, and all the cells of the meta-adenohypophysis. This crossreactivity could be blocked following pre-absorption with the appropriate n-kephalin, but not by pre-absorption with synthetic fl-endor-phin(1-31) or dynorphin(1-13). In addition, the enkepha-lin-like reactivity in the adenohypophysis of the lamprey was coincident with middle ACTH-like immunoreactivity in the pro-adenohypophysis and with aMSH-like immuno-reactivity in the meta-adenohypophysis. The absence of flLPH/fl-endorphin immunoreacfivity coincident with ACTH immunoreactivity, and the presence of enkephalin-like material in the adenohypophysis are un-ique to the lamprey