Electron microscopic findings in rat hypophysis after adrenalectomy and administration of ACTH. II. Neurohypophysis.

Electron-microscopic changes in the neural lobe of the rat hypophysis following adrenalectomy and a single administration of ACTH were studied. Twelve hours after adrenalectomy, a decrease in the amount of neurosecretory substances was observed, manifested by a small number of elementary granules of high electron density and, by the appearance of a great number of optically empty vesicles and masses of membrane-free material of low electron density. The increased secretion of neurosecretory substances after adrenalectomy seems to be related to the increased requirement of the organism for the ACTH-releasing factor. One hour after administration of ACTH, a picture was observed suggestive of the release of neurosecretory substances from the neural lobe fibers, which is probably connected with disturbances in the composition of blood electrolytes accompanying the excess of adrenocortical hormones.