Histological and Histochemical Studies on the Rat Pituitary Pars Intermedia

Abstract

The pars intermedia of the rat hypophysis was observed with the light microscope after staining with various histochemical methods. The results were compared with those of electron microscopy which have been published separately.
The pars intermedia may be divided into two parts, viz., the marginal zone facing the residual lumen of RATHKE's pouch and the pars intermedia proper situating dorsally to the former. When CIACCIO-fixed postchromicated paraffin sections are stained with HEIDENHAIN's azan method, the marginal zone preferably stains with orange G, while the pars intermedia proper with aniline blue. PAS staining followed by counterstain with mercuric bromphenol blue also differentiates the two parts, displaying the former blue and the latter purple.
Partial defect of the pars intermedia proper occurs frequently. In such a case the pars nervosa directly abuts the marginal zone. GOMORI-stainable substance probably corresponding to nerve fibers laden with neurosecretory substance frequently invades into the pars intermedia. In rare cases, ciliated cells occur among the epithelial cells lining the RATHKE's lumen or at the wall of cysts. In the latter case, goblet cells may be intermingled with the ciliated cells.
Glandular cells of the pars intermedia proper may be classified into two types, tha dark and light cells. The cytoplasm of the dark cell is PAS-positive and sudanophilic, and deeply stains with mercuric bromphenol blue. Various steps of transition between the dark and light cells are apparent especially in PAS preparations.
Colloid substance occurring in the lumen of RATHKE and in the cyst is also PAS-positive, sudanophilic and protein containing. It reacts positively to tests for SS and SH groups. Probable origin of the colloid was discussed.