High-resolution autoradiography of the adrenal medulla after injection of tritiated dihydroxyphenylalanine (dopa)

Abstract

Mouse and hamster adrenal medullae were studied by means of light and electron microscopic autoradiography at various time intervals after the injection of tritiated dehydroxyphenylalanine (dopa). The specimens were double-fixed with glutaraldehyde and osmium tetroxide. The electron microscopic autoradiography showed that at 30 minutes, 4 hours, as well as one week after injection the label was mainly localized to regions rich in chromaffin granules interpreted as indicating a rapid incorporation and a long-lasting storage in the granules of the catecholamines formed from the tritiated dopa. In the peripheral part of the hamster medulla, cell groups that correspond to the noradrenaline-producing cells ( 12 ) were found to be much more osmiophilic than the rest of the medulla when examined under the light microscope. In hamster adrenals studied 30 minutes after H 3 -dopa injection, the concentration of radioactivity was highest in the centrally located, lightly stained adrenaline-producing cells. Four hours and one week after injection the activity appeared evenly distributed in the two cell types of the hamster medulla. This indicates that the whole synthesis of adrenaline takes place in the adrenaline cells and that noradrenaline formed in the noradrenaline cells is not transferred to the adrenaline cells for further methylation. The adrenaline cells seem to have a more rapid turnover rate in spite of the extra methylation step.