Autoradiographic Demonstration of a Zonal Distribution of 3H-Dopamine-Derived Radioactivity in the Mouse Adrenal Medulla Perfusion-Fixed with Glutaraldehyde

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Abstract
Localization of 3H-dopamine-derived radioactivity in the chromaffin cells of the mouse adrenal medulla was studied by means of light microscopy and EM autoradiography. Twenty .mu.Ci/gbw [g body wt] of the isotope 3,4-dihydroxy (ring-G-3H) phenylethylamine hydrochloride was injected i.p. in 7 mice, which were then perfusion-fixed from the left ventricle of the heart with 2.5% glutaraldehyde from 15 min-24 h after injection. Following the post-osmication, dehydration through an ethanol series and Epon embedding, sections of pieces of the adrenal gland and liver were processed for autoradiography using the dipping method. Both A and N cells of the adrenal medulla showed maximum radioactivity at 30 min after isotope injection. The radioactivity on the A cells was higher than that on the N cells 15-30 min after injection. Both types of chromaffin cells contained a similar amount of radioactivity at later time points. At all time points examined, both A and N cells were highest in the 3H-dopamine-derived radioactivity in the zone immediately beneath the corticomedullary junction, whereas the radioactivity in the central portion of the adrenal medulla was always lower. No difference was demonstrated between the ultrastructure of the heavily labeled chromaffin cells and that of the lightly labeled cells. No regional difference in the 3H-dopamine-derived radioactivity was demonstrated in the liver lobules. No zonal distribution of radioactivity was demonstrated in autoradiograms of the mouse adrenal medulla prepared after the 3H-leucine (L-leucine-4,5-3H) injection. These results are consistent with the idea that the chromaffin cells in the zone immediately beneath the cortico-medullary junction of the mouse adrenal gland have a greater dopamine-handling capacity than those in the central portion of the adrenal medulla and that this phenomenon is characteristic of dopamine.