| Abstract: | Zona glomerulosa cells of the rat adrenal cortex were studied at 2, 6, 12, 18 and 24 months. Adrenals from unstimulated rats were processed for light and electron microscopy and trunk blood was obtained for the assay of plasma renin activity and aldosterone. Similar assays were made in rats stimulated with adrenocorticotropic hormone (ACTH), 30 min before sacrifice. At light microscopy, no major structural changes were observed; the ultrastructure of most organelles was well preserved and the presence of lipofuscin granules in older animals was remarkable. Acid phosphatase activity was observed in lysosomes and some lipofuscin granules. The quantitative study showed an age-related decrease in cell and nuclear volume (p < 0.01 and p < 0.001 respectively) and an increase in volume density of lipid droplets, lipofuscin granules (p < 0.001), lysosomes and Golgi complex; a decrease in volume density of mitochondria and smooth endoplasmic reticulum (p = 0.052) was also observed. Plasma renin activity and aldosterone level were both reduced (p < 0.001). In stimulated animals, an enhanced aldosterone level was obtained which was higher at 12 months and decreased thereafter. These results show an age-related decrease of aldosterone secretion, consistent with structural and ultrastructural data and related to plasma renin decrement. They also show a decline in the response to aldosterone stimulation by ACTH, indicating a lesser functional ability of zona glomerulosa cells in old animals. |
