Molecular Pharmacology, Vol 5, 342-349, Copyright © 1969 by the American Society for Pharmacology and Experimental Therapeutics

Mechanism of Secretion from the Adrenal Medulla

V. Retention of Storage Vesicle Membranes following Release of Adrenaline

¹ Department of Biochemistry, Duke University Medical Centre, Durham, North Carolina 27706

Dopamine -hydroxylase (EC 1.14.2.1) was used as a marker to follow the fate of the adrenal storage vesicles following the release of adrenaline. Neurogenic secretion of adrenaline induced by insulin produced a decrease in the adrenaline and dopamine -hydroxylase contents of the gland. There was only a slight decrease in the enzyme activity of the particulate fraction obtained from lysed storage vesicles, but a marked decrease in the activity of the soluble fraction. Twenty-four hours after the administration of reserpine (1 mg/kg) to rabbits, changes in the dopamine -hydroxylase activity were similar to those observed after insulin treatment, but the glands were more severely depleted of their catecholamines. After lower doses of reserpine (0.25 mg/kg), or if ganglionie transmission was blocked by chlorisondamine 1 hr prior to the administration of reserpine (1 mg/kg), there were significant decreases in the catecholamine content but no changes in the dopamine -hydroxylase activity. These findings indicate that neurogenic secretion is characterized by release of the soluble content of the storage vesicles directly to the exterior of the cell and retention of the storage vesicle membranes within the cell. Interference only with time uptake or storage mechanism by reserpine results in depletion of the catecholamine content, but not of the intravesicular protein.