Effects of ACTH on membranous whorls in the adrenal gland of the Mongolian gerbil

The ultrastructure of whorls of rough endoplasmic reticulum in the adrenal gland of the Mongolian gerbil (Meriones unguiculatus) was examined during and after treatment with ACTH. Whorls were loosely wound after treatment for one day and consisted of only a few paired membranes. Focal areas of increased tubular smooth endoplasmic reticulum were seen throughout the cytoplasm of the cells. Whorls disappeared altogether after three days of ACTH treatment. The structures reappeared one day after stopping the ACTH injections and seemed to enlarge progressively by addition of membranes to the periphery of the structures. Numerous vesicles and sometimes parallel cisternae of rough endoplasmic reticulum were observed in the cytoplasm of adrenocortical cells containing newly forming whorls. The whorls apparently serve as a readily available reserve of rough endoplasmic reticulum, which can transform into smooth reticulum upon stimulation with ACTH.