Functional morphology of the pars intermedia of the rat hypophysis as revealed with the electron microscope

Summary

The pars intermedia of the hypophysis of normal and experimental rats was studied by electron microscopy. Observations of the hypophysis at various intervals following formalin induced stress or adrenalectomy indicate the existence of a functional relationship between the posterior lobe, the pars intermedia, and the adrenal cortex.

Glandular cells of the normal pars intermedia are divided into two types, i. e., the light and dark cells. The former type dominates in number and is characterized by a large amount of cytoplasm filled with clear vesicles 250–350 mμ in diameter. Dark secretory granules smaller than 300 mμ are few in number and restricted to the Golgi region.

After a single injection of formalin, the clear vesicles of the light cell dimmish and dark secretory granules varying in opacity increase in number. Transition from dark granules to clear vesicles is suggested. Three to five days after adrenalectomy, the light cells contain an abundance of moderately dense vesicles which are smaller than the larger more electron lucent vesicles of the normal light cells. The moderately dense vesicles are about 200 mμ in diameter and are extremely abundant filling the entire cytoplasm of the light cells 7 days after adrenalectomy.

Bundles of unmyelinated nerve fibers are often observed in the pars intermedia, and a typical neuroglandular synapse was found in the pars intermedia of a sham-operated animal suggesting neural control of the secretion process of pars intermedia cells.