Corticotroph (Basophil) invasion of the pars nervosa in the human pituitary: Localization of proopiomelanocortin peptides, galanin and peptidylglycine α-amidating monooxygenase-like immunoreactivities.

Corticotroph (basophil) invasion or the migration of corticotroph cells into the pars nervosa of the human pituitary gland was found in 35 of 767 (4.4%) consecutive pituitaries obtained at autopsy. The degree of invasion increased with patient age and extensive invasion was more common in men than in women. Immunoreactive ACTH, β-MSH, α-MSH, and galanin were detected both in the anterior lobe and invading corticotroph cells in approximately equal frequency. Fewer cells stained positively for α-MSH than for the three other peptides in both the anterior lobe and invading corticotrophs. Twelve corticotropic pituitary adenomas obtained surgically from patients with Cushing's disease were also examined and expressed varying degrees of immunoreactivity for ACTH, α MSH, β-MSH and galanin. Staining for all major pituitary hormones revealed only ACTH in the invading basophil cells. Peptidylglycine α-amidating monooxygenase (PAM) was present in the anterior pituitary, in invading corticotroph cells, and in some cells lining the cysts of the pars intermedia zone. PAM immunoreactivity was also detected in 4/12 corticotroph adenomas. These results indicate that corticotroph cells invading the pars nervosa are immunohistochemically similar to anterior lobe corticotrophs and have the ability to amidate various peptides such as proopiomelanocortin cleavage products and galanin with PAM.