Colchicine inhibited amylase secretion by isolated rat parotid glands only 6 h after administration of the drug in vivo. This delayed effect was not the result of the inability of the drug to reach its reaction site. When parotid glands were emptied of their secretory granules by isoproterenol treatment, the subsequent replenishment of cells with granules was inhibited by colchicines. Colchicine concomitantly produced alterations of the Golgi complexes, the cisternae of which were reduced in size and surrounded by clusters of microvesicles. Incubation of parotid glands with colchicines for prolonged durations failed to alter stored amylase secretion as stimulated by isoproterenol, but it inhibited the release of de novo synthesized enzyme. Another colchicines-binding activity, firmly bound to the particular fraction of homogenates, was found, of which a part may represent membrane located microtubular protein. An assembly-disassembly cycle of microtubules appears to exist in the parotid gland, as in the liver. However, only 14 percent of tubulin was found to be polymerized as microtubules in parotid glands as opposed to 40 percent in the liver. The present data suggest that colchicine primarily inhibits the transfer of secretory material towards or away from the Golgi complexes but not the hormone-stimulated secretion of stored amylase.

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