Pituitary intermediate lobe cysts: their formation and contribution to intraglandular (residual lumen) colloid.

3 types of bovine pituitary intermediate lobe cysts referred to in the present study as type 1, 2 and 3, normally occur in the deep zone of the intermediate lobe. The deep zone of the intermediate lobe, like the entire lobe, is composed entirely of basophilic cells which make contact and invade the posterior lobe. The deep zone abuts the marginal zone which faces the intraglandular lumen (residual lumen) between the anterior and intermediate lobe. The marginal zone is readily distinguished from the deep zone since cysts do not form there and the cells in the marginal zone continually break down into a colloid-like material that sloughs into the intraglandular lumen. The major characteristics of the type 1 cyst is the constant addition of intermediate lobe cells to its peripheral ring and the presence of an isolated clump of unknown material in the colloid. The type 2 cyst is characterized by the continual disintegration of its peripheral cells which are cast into the cavity forming its contents. The type 3 cyst is characterized by a peripheral ring made up of a single layer of basophilic intermediate lobe cells as well as a limiting membrane which surrounds the cavity of the cyst. Intermediate lobe cysts may be a reservoir of active intermediate lobe materials. It is widely accepted that intermediate lobe cells synthesize a family of peptide hormones and a recent study shows that intraglandular colloid housed in the intraglandular lumen (residual lumen) contains intermediate lobe peptide hormones ACTH, alpha MSH and beta LPH.