Maturation of the adrenal medulla—II: Content and properties of catecholamine storage vesicles of the rat

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Albino Wistar rats were sacrificed at 10-day intervals from birth to 50 days of age. The adrenals were analyzed for catecholamines (CA) and dopamine β-hydroxylase (DBO), and purified storage vesicles were analyzed for CA and ATP. At birth, all three parameters were 3–5 per cent of 50-day levels, about 10 per cent at 10 days, 20–30 per cent at 20 days, 40–55 per cent at 30 days and 70–75 per cent at 40 days. Although all three increased approximately in parallel, CA/DBO was below normal from birth to 20 days and CA/ATP was above normal at 10 days. At birth, the vesicles were more fragile, but discontinuous density gradient studies indicated fewer “light” vesicles (vesicles deficient in CA and ATP which do not penetrate 1.6 M sucrose) compared to adults. At 10 and 20 days, however, more light vesicles were present and vesicle fragility was the same as in adults. Neonates did not secrete adrenal CA in response to insulin-induced hypoglycemia, but secretion was observed at all other ages. Isolated neonatal adrenals as well as adult adrenals exhibited Ca 2+-dependent CA secretion when exposed to high K + concentrations. These data suggest that there are age-dependent changes in the content and properties of adrenal CA storage vesicles which affect the uptake and storage of amines in the vesicles. The maturation of vesicles is probably dependent on the relative rates of synthesis of vesicle components, which in turn are affected by the degree of neural input to the gland.