Electron microscopic observation on the adrenal medulla and extra-adrenal chromaffin tissue of the postnatal rabbit.

typical chromaffin during in the preaortic and in the of the developing adrenal electron-dense granular inclusions of a type which corresponds to typical chromaffin granules were observed in primitive sympathetic cells they were present in small numbers in phaeochromoblasts and were abundant in typical chromaffin cells. The mean size of adrenal medullary chromaffin granules increased from c. 60 nm in 14 d-old foetuses to 148 nm (adrenaline storing) or 86 nm (noradrenaline storing) in 28 d-old foetuses while the extra-adrenal granules remain at a mean diameter of 62 nm.