Evidence that the secreting adrenal chromaffin cell releases catecholamines directly from ATP-rich granules.

1. Cats' adrenal glands were perfused with Locke's solution and stimulated through the splanchnic nerves or by acetylcholine.2. In response to such stimulation there appeared in the venous effluent, in addition to catecholamines, large amounts of AMP and adenosine and smaller amounts of ATP and ADP. Like the catecholamines, these substances had their origin in the chromaffin cells as was shown by their failure to appear when the splanchnic nerves were stimulated during perfusion with drugs blocking the adrenal synapses.3. During stimulation the ratio of catecholamines: ATP and metabolites in the venous effluent corresponded closely with the reported ratio of catecholamines: adenine nucleotides in the ;heavy' chromaffin granules.4. Adenine nucleotide appeared in the adrenal effluent pari passu with catecholamines within a second or two of beginning stimulation.5. It is concluded that the nucleotide-rich granules are the immediate source of catecholamines released from the stimulated adrenal chromaffin cell, and that the other two intracellular ;pools' that have been described, nucleotide-poor and ;free' cytoplasmic catecholamines, contribute little or not at all.