Opiate receptor mediated internalization of I-?-endorphin in human polymorphonuclear leucocytes

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Abstract
The early events in the interaction of (125I)-Tyr27-.beta.-endorphin with human polymorphonuclear leucocytes were investigated. Using ultrastructural autoradiography we found that the labeled peptide specifically bound to the plasma membrane and was internalized within two minutes of incubation at 37.degree. C. Both processes could be inhibited by unlabeled .beta.-endorphin or by the opiate antagonist diprenorphine. This finding was confirmed by radioreceptorassays. With longer incubation times the specific association of the labeled .beta.-endorphin with the cells decreased. About 10% of the tracer was degraded within 10 min of incubation as shown by gel chromatography. The morphological changes induced by 125I-.beta.-endorphin the granulocytes were investigated under the microscope. The labeled peptide had the same biological effect as unlabeled .beta.-endorphin.