The development and maturation of adrenal medullary chromaffin cells of the rat in vivo: a descriptive and quantitative study.

A descriptive account and morphometric study of the adrenal medulla and adrenal chromaffin cells of Wistar rats aged from birth to 22 months is presented. Distinct adrenaline and noradrenaline-storing types of chromaffin cells are first identified in 4-day-old animals, prior to that time individual cells contain both adrenaline- and noradrenaline-storing granules. Primitive sympathetic cells and phaeochromoblasts occurs up to 2 days postnatally. Mitotic figures occur in chromaffin cells of a maturity and appearance appropriate to age and most frequently in adrenaline-storing cells. The adrenal medulla continues to increase in volume throughout the period and chromaffin cells increase in number and in some cases volume. There is a corresponding increase in neuronal elements. In 22-month-old rats individual cells or groups of chromaffin cells show evidence of hypertrophy and changes in cytoplasmic organelles, in particular lysosomes, rough endoplasmic reticulum and storage granules and vesicles. Some hypertrophied chromaffin cells contain a heterogeneous population of granules suggesting a degree of functional plasticity in some cells in aged rats.