Study of the effects of aging on macromolecular synthesis in mouse steroid secreting cells using microscopic radioautography.

Abstract

The effects of aging on DNA, RNA and protein synthesis in adrenal gland cortical cells and testicular Leydig cells of ddY mice at various ages (from prenatal day 19 to postnatal days 1, 3, 7, 14, months 1 and 6 and 1 and 2 years after birth) were examined using light and electron microscopic (EM) radioautography after labeling with [3H]-thymidine, [3H]-uridine and [3H]-leucine. The percentage of the labeled cells in the adrenal glands after [3H]-thymidine injection was greatest in the zona glomerulosa of the cortex and the medulla on embryonic day 19, in the zona fasciculata and zona reticularis of the cortex on postnatal day 1 and gradually decreased with aging. EM radioautography revealed that well developed cell organelles such as smooth surfaced endoplasmic reticulum, Golgi apparatus, mitochondria with tubular cristae and lipid droplets were more frequently observed in the cytoplasm of unlabeled cells as compared to cells labeled with [3H]-thymidine in the three zones of the cortex. The effects of aging on RNA synthesis in adrenal glands after [3H]-uridine injection revealed that all types of cells of the adrenal gland were labeled. In each cell, silver grains were localized over the nuclei and cytoplasm and were more dense in the nuclei than the cytoplasm. Grain counts were highest in the cortex and medulla on fetal day 19 and then gradually decreased with aging from postnatal day 14 to 1 year after birth. In the cortex, the number of silver grains was higher in the zona glomerulosa than in the other zones from fetal day 19 to 1 year and grain counts were higher in the medulla in the embryonic stage as compared to the postnatal stages. However, the number of labeled mitochondria and the mitochondrial labeling index increased with aging. The [3H]-thymidine labeling index in the Leydig cells of the testis was low at embryonic and early postnatal stages, increased slightly at 6 months and reached a peak at 9 months which was maintained at a relatively high level in senescence. The number of the silver grains over the nuclei and cytoplasm of Leydig cells due to [3H]-uridine labeling was observed from embryonic day 19 and increased from month 3 onwards. From adult to senescence, [3H]-uridine incorporation was maintained at high levels in the nuclei and was relatively low in the cytoplasm. The effects of aging on [3H]-leucine incorporation in Leydig cells were also examined. The labeling indices between embryonic and early postnatal stages showed no obvious differences although the number of the silver grains in both cytoplasm and nucleus increased from 6 months onwards and was maintained at high levels until senescence. From these results, it was concluded that the effects of aging on DNA, RNA and protein synthesis in steroid secreting cells such as adrenal gland cortical cells and testicular Leydig cells of mice correlated with the hormonal changes observed with aging.