Non-neurogenic adrenal catecholamine release in the neonatal rat: exocytosis or diffusion?

When subjected to stress, neonatal rats secrete adrenal catecholamines by a mechanism which does not require nerve stimulation. To test whether the non-neurogenic secretory mechanism involves exocytosis, we examined the effects of hypoxia (a non-neurogenic stimulus) and nicotine (a stimulus which simulates neurogenic input) on catecholamine levels and on the uptake of [3H]epinephrine into chromaffin granules. Hypoxia- and nicotine-induced depletion of catecholamines were both accompanied by a reduction in uptake, indicating a loss of granule integrity which is characteristic of exocytosis. Although a significant proportion of adrenal catecholamines was found to be extragranular, only the granular pool was involved in the secretory response.