The effect of morpine dependence on the vesicular content of adrenergic nerves in relation to arteriolar smooth muscle in the pancreas of the rat.

1. Sibling male Wistar rats were kept in groups of three under identical conditions. Two groups were made morphine dependent in 28 days and the third served as control. The state of dependence was established by recording the development of tolerance to the analgesic action of the drug and the effect of acute withdrawal of morphine and injection of nalorphine on one test group.2. Animals in the other test group and the control group were killed and specimens of pancreas collected and prepared for examination by electron microscopy. The adrenergic innervation of pancreatic arterioles was located and photographed and the effect of morphinization on the percentage of granular and agranular small vesicles in the axons determined.3. Morphinization produces a significant reduction in the granular or dense core vesicle population of these adrenergic axons.