Investigations on the secretion mechanism of corticosteroid hormones

Morphometrical and biochemical findings favouring the view that an exocytotic mechanism is involved in the release of corticosteroid hormones are reviewed. Acute stimulation provokes a notable increase in the number of dense granules in adrenocortical cells of some mammalian species. Stereology shows that the increase in the volume density of granules is of the same order of magnitude as that of the intracellular concentration of corticosteroid hormones, as evaluated by radioimmunological techniques. Electron dense granules do not display cytochemically demonstrable peroxidase or acid-phosphatase activity, and the increase in their volume density is not associated with an enhanced activity of many typical lysosome enzymes. Vinblastine, an antimicrotubular agent which interferes with exocytotic mechanisms, induces a parallel rise in both the volume density of granules and the intracellular hormonal concentration. The putative granular fraction, isolated by differential centrifugation from adrenal homogenates obtained from vinblastine and ACTH treated rats, possesses a corticosterone concentration higher than other subcellular fractions, excluded postmicrosomal supernatant.