Adenohypophysial cell types in the pituitary of adult sea lampreys, Petromy
zon marinus, was localized by means of immunocytochemical and lectin cytoch
emical techniques. At least four types of adenohypophysial hormone cells ar
e present in the pituitary of adult sea lampreys. The first type of cell is
ACTH-like and occupies most parts of the rostral pars distalis (RPD), but
a few scattered ACTH-like cells are also present in the proximal pars dista
lis (PPD). The second type of cell is MSH-like and occupies the whole pars
intermedia. The third type of cell is GH/PRL-like and occupies the dorsal h
alf of the PPD. These GH/PRL-like cells were initially detected by heterolo
gous immunocytochemistry using antibodies to salmon GH, salmon PRL and blue
shark GH, after hydrated autoclave pretreatment of sections. Later, by use
of an antiserum raised against a synthetic peptide corresponding to the pa
rtial sequence of lamprey GH/PRL, the same cells as those containing GH/PRL
-like immunoreactivity were stained positively. Similarity of the topograph
ic distributions between lamprey GH/PRL-like cells and gnathostome fish GH
cells in the pituitary suggests that GH/PRL-like cells in the lamprey may b
e GH cells. The last type of cell is GTH-Iike and occupies the Ventral half
of the PPD. Although GTH has not yet been isolated from the lamprey pituit
ary, our immunocytochemical data suggest that GTH-like material in the sea
lamprey pituitary is more closely related to mammalian-like LH, rather than
to FSH or TSH. These four types of adenohypophysial cells occupy most part
s of the lamprey adenohypophysis and indeed there is little room for TSH or
PRL cells. Thus, the present study further suggests that GH and LH-like GT
H are ancestral forms of GH/PRL/SL family and glycoprotein hormones, respec
tively. (C) 2001 Elsevier Science Inc. All rights reserved.