Galanin (GAL) pituitary expression, mRNA (Ponchon et al,(2000) J. Neuroendocrinol 12:559-564) and peptide (O'Halloran et al, (1990) Endocrinology 127: 467-475), are under estrogen influences. Molecular action of GAL on the anterior pituitary is mediated by GAL receptor 2 (GALR2), which is involved in the regulation of PRL and GH (Ottlecz et al, (1998) PNAS 85:9861-9865,Depczynski et al,(1998) Ann N Y Acad Sci 863:120-1284). Using immunohistochemical techniques, we studied GAL and GALR2 profile,as well as their cellular distribution and the coexistence of GAL with estrogen receptor a (ERa) in the anterior pituitary of female rats throughout the estrous cycle.

The highest number of GAL-immunoreactive (-ir) cells was detected at pro-estrous-noon, and the lowest at proestrous-afternoon and estrous. GAL was present in cells that were also PRL-ir (56% at proestrous-morning, 25% at metaestrous and diestrous, and 10% at pro-estrous-afternoon and estrous), TSH-ir (15% at metaestrous and diestrous, 5% at pro-estrous-morning, pro-estrous-afternoon and estrous), or GH-ir (few positive cells along the cycle). Double immunostaining for ERa-GAL in all peptide expressing cells was observed. GALR2-ir was detected along the estrous cycle in all anterior pituitary cells, except at proestrous-noon, when only disperse groups of cells with the strongest staining intensity were observed. All hormone pituitary-producing cells were GALR2-positive at diestrous-morning and were undetectable in corticotrophs at proestrous-noon.

Our results indicate that anterior pituitary GALR2 expression is steroid hormone dependent, and suggest a functional relationship between GAL and estrogen in the anterior pituitary gland regulation. Supported by SAF2004-08316-C02-01 (MEC, Spain)