IMMUNOHISTOCHEMICAL LOCALIZATION OF ENKEPHALINS IN MEDIAN-EMINENCE AND ADENOHYPOPHYSIS

Immunohistochemical staining for methionine-enkephalin and leucine-enkephalin were used to reveal an enkephalin-like substance in the median eminence and adenohypophysis of guinea pig and rat. Nerve endings were stained for enkephalins in the external layer of the median eminence. By successive staining of two different antigens, somatostatin fibers in the guinea pig were also shown to be enkephalin-immunoreactive. Staining of the adenohypophysis varied with the species and the antisera used. Intermediate lobe and corticomelanotrophs were stained moderately. In both species, and with all the antisera, thyrotrophs were shown to contain an immunoreactive substance. In the guinea pig, gonadotrophs were stained particularly by the anti-leucine-enkephalin antiserum used. The locus of enkephalin action on pituitary functions can be discussed: enkephalins possibly have an inhibiting action on somatostatin fibers, which agrees with the stimulating action of enkephalins on GH already known. Furthermore, enkephalins could have a direct action on pituitary glycoprotein producing cells, which would explain their inhibiting action demonstrated previously on LH, FSH and TSH. © 1979.