Electron microscopic studies were made on the morphological changes of mitochondria of the adrenal cortex of young and mature rats under various experimental conditions : administration of ACTH, DOCA, chorionic gonadotrophin and KC1 with accompanying decrease in Na/K ratio, removal of hypophysis, etc. Correlation between the ultrastructure of the adrenal cortex and its function was sought.
1) Mitochondria can be classified into two types according to the structure of the internal membrane : type I with the internal membrane possessing crista-like or filament-like structure and type II with the internal membrane of honeycomb-like structure. The former is mainly found in the zona glomerulosa and the latter in the zona fasciculata and reticularis. As the rat matures or as hyperfunction of the adrenal cortex develops, the type I mitochondria become more complex in structure with the protruding structure of the internal membrane forming a fine network. The type 1 mitochondria are transformed into type II. When hyperfunction of the adrenal cortex persists, the limiting membrane of mitochondria breaks and the internal structures of mitochondria come into contact with the endoplasmic reticulum surrounding the mitochondria.
2) The structure of mitochondria in the zona glomerulosa is altered when either the Na/K ratio is lowered or DOCA is administered. A similar change can be observed with the adminisiration of ACTH or by hypophysectomy. The function of the zona glomerulosa, therefore, seems to be under the influence of the alteration of the Na/K ratio as well as the function of the hypophysis, though to a lesser extent.
3) With the administration of chorionic gonadotrophin, a tubular structure appears in the type II mitochondria in the inner layer of the zona fasciculata and in the outer layer of the zona reticularis. This structure, after six weeks administration of chorionic gonadotrophin, changes into a vacuolar structure.
These changes in the mitochondria differ from those seen after the administration of ACTH, e.g., disappearance of the fine structure in the internal membrane of the type II mitochondria in the outer layer of the zona fasciculata and opening of the limiting membrane.