Ultrastructure of the adrenal medulla of normal and insulin-treated hamsters

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Abstract
Fine structural characteristics of the chromaffin cells both in normal and insulin-administered hamster adrenal gland were studied. Exocytosis occurs in 5 per cent of nonstimulated cells especially on the apical cell surfaces. At the same time the occurrence of a great number of closely attached secretory granules was conspicuous on the lateral plasma membrane in the untreated hamster adrenal medulla. Following insulin treatment (10IU/100g/body weight), characteristic was the development of large intercellular vacuoles between the lateral plasma membrane, in which electrondense secretory material was frequently present. On the basis of this observation it is suggested that in the case of insulin-induced hormone secretion, exocytosis preferentially occurs on the lateral plasma membrane, and may play an important role in the discharge of secretory materials from the cells.