The effects of chronic administration of ACTH and dexamethasone on the morphology of mitochondria inzona glomerulosacells of the rat adrenal cortex were investigated by Stereological techniques. It was found that the volume of the mitochondrial compartment as well as the surface of the outer and inner mitochondrial membranes were significantly increased or decreased in relation to the number of days of ACTHor dexamethasone-treatment. In ACTH-administered rats, the average volume of individual mitochondria decreased significantly up to the 6th day of treatment and then showed a conspicuous increase from the 6th to the 15th day, whereas in dexamethasone-administered animals this parameter, after a small increase during the first 6 days of treatment, displayed a significant decrease. The number of mitochondria per cell showed a dramatic increase during the first 6 days of treatment with ACTH and continued to increase, but only slightly, with the subsequent treatment. In contrast, this parameter showed a parabolic decrease as a function of the duration of treatment in animals receiving dexamethasone. In the light of evidence showing that dexamethasone blocks ACTH-release, these findings are discussed and interpreted to indicate that ACTH is involved in the maintenance and stimulation of the growth and proliferative activity of mitochondria in rat adrenalzona glomerulosa.
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