Role of β-endorphin in the regulation of proinflammatory cytokine production by peripheral blood monocytes in vitro

β-Endorphin activated interleukin-1β production in the culture of unfractionated cells with lipopolysaccharide, but had no effect on the synthesis of tumor necrosis factor-α and interleukin-6. This peptide produced a slight stimulatory effect on spontaneous production of interleukin-1β by cultured leukocytes. Opioid receptor blockade with naloxone and naltrindole did not abolish the stimulatory effect of β-endorphin on interleukin-1β production. β-Endorphin did not modulate the synthesis of interleukin-1β, tumor necrosis factor-α, and interleukin-6 in a purified fraction of monocytes.