Age-related changes in the inner zone of the adrenal cortex of the rat - amorphologic and biochemical study

In this work, a correlative morphologic and biochemical study on the effect s of ageing on the rat adrenal Inner Zone (IZ) was made, Male Wistar rats w ere studied at 2, 6, 12, 18 and 24 months. Structural data of Zona Fascicul ata (ZF) showed age-related increase in cell volume (P < 0.05), decrease in mitochondria (P < 0.01) and smooth endoplasmic reticulum (SER) volumes, an d increase in lipid droplets (P < 0.01) and lipofuscin granules (P < 0.01) volumes. In Zona Reticularis, the main change observed was the increase in lipofuscin granules (P < 0.001). Serum corticosterone from unstimulated rat s increased until 12 months but decreased thereafter (P < 0.01), to levels below those from 2-month-old rats. Similarly, plasma adrenocorticotrophic h ormone (ACTH) presented a maximum at 12 months, followed by a decrease to l evels higher than at 2 months (P < 0.05). In rats injected either with only ACTH or dexamethasone, before ACTH stimulation, corticosterone level had a maximum at 12 months. In aged rats, serum high density lipoprotein (HDL) a nd adrenal cholesterol ester increased significantly (P < 0.05 and P < 0.01 , respectively), whereas adrenal corticosterone decreased. Products of lipi d peroxidation, assayed with the thiobarbituric acid reaction and fluorimet ry showed an age-related increase (P < 0.05). The age-related decrease in m itochondria and SER volumes is consistent with the decrease of serum cortic osterone. The increase in lipid droplet and HDL and the reduction of adrena l corticosterone level correlate with the increase of adrenal cholesterol e ster content. These suggest a continued uptake of steroid precursor but a r educed steroid synthesis. On the whole, the data provide evidence for an ag e-related reduced functional ability of IZ and particularly of ZF. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.