Ontogenesis of chromogranin A and B and catecholamines in rat adrenal medulla.

The ontogenesis of chromogranins A and B and catecholamines was investigated for rat adrenal medulla. The chromogranins, the major secretory peptides of chromaffin granules, were characterized by one- and two-dimensional immunoblotting. Chromogranin B appeared identical in fetal and postnatal adrenals. On the other hand a significant portion of chromogranin A immunoreactivity in fetal adrenals was present in a component which was identified as a proteoglycan form of chromogranin A. In adult adrenals this proteoglycan chromogranin A was different and much less prominent. Total chromogranins and catecholamines increased parallely from the 17th prenatal day to the adult stage. However in early periods of development chromaffin granules are likely to contain relatively higher catecholamine levels than adult granules. At the end of the gestational period both the ratio of adrenaline to noradrenaline and of chromogranin A vs B increases sharply. These results establish that from the 17th prenatal day onward fetal adrenal glands contain chromaffin granules which are filled with both the major secretory peptides and catecholamines. The relative composition of the secretory content (adrenaline vs noradrenaline and chromogranin A vs chromogranin B) changes at the end of the gestational period in parallel with the development of the corticosteroid-producing adrenal cortex.