THE ZINC POOL IS INVOLVED IN THE IMMUNE-RECONSTITUTING EFFECT OF MELATONIN IN PINEALECTOMIZED MICE

Melatonin (MEL) affects the immune system by direct or indirect mechan isms. An involvement of the zinc pool in the immune-reconstituting eff ect of MEL in old mice has recently been documented. An altered zinc t urnover and impaired immune functions are also evident in pinealectomi zed (pr) mice. The present work investigates further the effect of ''p hysiological'' doses of MEL on the zinc pool and on thymic and periphe ral immune functions in pr mice. Daily injections of MEL (100 mu g/mou se) for 1 month in px mice restored the crude zinc balance from negati ve to positive values. Thymic and peripheral immune functions, includi ng plasma levels of interleukin-2, also recovered. The nontoxic effect of MEL on immune functions was observed in sham-operated mice. Becaus e the half-life of MEL is very short (12 min), interruption of MEL tre atment in ox mice resulted, after 1 month, in a renewed negative crude zinc balance and a regression of immune functions. Both the zinc pool and immunological parameters were restored by 30 further days of MEL treatment. The existence of a significant correlation between zinc and thymic hormone after both cycles of MEL treatment clearly shows an in volvement of the zinc pool in the immunoenhancing effects of MEL and t hus suggests an interrelationship between zinc and MEL in pr mice, Mor eover, the existence of significant positive correlations between zinc or thymulin and interleukin-2 suggests that interleukin-2 may partici pate in the action of MEL, via zinc, on thymic functions in px MEL-tre ated mice.