EVIDENCE FOR AN OPIOID INHIBITORY EFFECT ON T-CELL PROLIFERATION

The proliferative response of human or rat T lymphocytes to phytohemag glutinin (PHA) or concanavalin A (ConA) was measured after acute (30 m in) or chronic (8 days) treatment with the opiate receptor antagonists naloxone or naltrexone. Both in the rat and in the human, proliferati on was significantly enhanced by acute treatment with the opiate recep tor antagonists. In contrast, after chronic treatment proliferation al ways decreased. The sudden removal of an opioid inhibitory tone might be the basis for the increased proliferative responses observed after acute treatment. The decrease after chronic treatment could be ascribe d to the amplification of the inhibitory effect of endogenous opioids due to the up-regulation of opiate receptors that follows chronic anta gonist administration. Receptor binding studies of beta-endorphin rece ptors on splenocytes of chronically naloxone treated rats confirmed th is hypothesis: a higher number of beta-endorphin receptors were expres sed on splenocytes of naloxone-treated rats compared to controls (B(ma x) = 9.8 x 10(-12) VS. 1.1 6 x 10(-12), respectively).