Colchicine inhibits adrenal medullary secretion evoked by acetylcholine without affecting that evoked by potassium.

In perfused rabbit adrenal glands, colchicine (500 muM) inhibited the catecholamine secretion evoked by acetylcholine (20 mug/ml) but not that evoked by excess potassium (60 mM). Since both stimuli are believed to release catecholamines ultimately by the same secretory process, exocytosis, it is concluded that these inhibitory effects of colchicine exerted against acetylcholine result from an action early in the process of stimulus-secretion coupling, possibly at the level of the acetylcholine receptor, and that it is inappropriate to use such inhibitory effects to support the view that secretion proper (exocytosis) in chromaffin cells involves colchicine-sensitive elements such as microtubules.