Adult male albino rats are decapitated and the mitochondria in one adrenal gland are examined at increasing post‐mortem time intervals in the electron microscope. The contralateral adrenal gland is excised rapidly, immersed in aldehyde fixative, diced, and used as the control. As early as 15 minutes postmortem, tightly packed sheaves of tubules (each tubule measuring 140 AR in outside diameter) appear as inclusions in the matrix of mitochondria within the zona fasciculata. These inclusions occur in increasing numbers of mitochondria during the first hour postmortem, until 10‐25% of the mitochondria examined contain at least one sheaf of tubules. Observations at two and three hours post‐mortem reveal no significant increase in inclusion‐containing mitochondria. At these late time intervals additional post‐mortem alterations are evident: (1) a decrease in mitochondrial matrix density; (2) swelling of mitochondrial cristae; and (3) vesiculation of the smooth reticulum. Kjaerheim ('67), Wheatley ('68), and Magalhaes and Magalhaes ('68) have described tubular inclusions in the matrix of “normal” rat adrenal mitochondria which are identical to the post‐mortem inclusions described in this study. The presence of such inclusions in control mitochondria has been observed by the author on one occasion: within a degenerate mitochondrion enclosed inside a cytoplasmic membrane‐limited vacuole. The possible significance of this post‐mortem mitochondrial alteration in the rat adrenal cortex is discussed. Copyright © 1969 Wiley‐Liss, Inc.
