Biochemical Characterization of Naloxone-Resistant Receptors for B-Endorphin on a Human Mononuclear Cell Line (U937) and Murine Splenocytes
β -Endorphin and the opiate alkaloids affect a variety of leukocyte functions which are involved in host defense and immunity. These effects can be separated according to their sensitivity vs resistance to inhibition by naloxone. Modulation of monocyte (1) and stimulation of polymorphonuclear leukocyte superoxide generation (2,3), inhibition of lymphocyte gamma-interferon secretion in response to concana-valin A (4), enhancement of natural killer (NK) cell activity (5,6), and opioid-induced inhibition of the antibody response to sheep erythrocytes (7) are all reversed by the opiate receptor antagonist, naloxone. These responses may depend on the activation of opiate receptors such as the mu-like (8) and delta opiate receptors (9) which have been partially characterized on murine splenocytes and human peripheral blood mononuclear cells. The mu-like site was sensitive to displacement by naloxone or morphine and completely resistant to ß-endorphin and leucine or methionine enkephalin. In contrast to these responses which are apparently mediated by opiate receptors, the effects of β-endorphin on mononuclear cell proliferative responses (10–12), interleukin-2 production (13), and calcium uptake (14) are resistant to inhibition by naloxone.
KeywordsU937 Cell Human Peripheral Blood Mononuclear Cell Opiate Receptor Scatchard Analysis High Affinity Binding Site
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