Immunotoxicological examination of repeated dose combined exposure by dimethoate and two heavy metals in rats

Abstract

The immunotoxicity of 28 days combined oral exposure by dimethoate (DM) and two heavy metals (Pb or Cd) was investigated in male Wistar rats. Immunotoxic and no-effect doses of DM (28.2 and 7.04 mg/kg) were combined with immunotoxic and no-effect doses of CdCl2 (6.43 and 1.61 mg/kg) or lead acetate (80.0 and 20.0 mg/kg) in such a way that the high dose of each substance was given in combination with the no-effect dose of the other. To examine the interactions of these agents, general toxico-logical (body weight gain, organ weights), haematological (absolute and differential WBC, RBC, MCV, Ht, cell content of the femoral bone marrow), and immune function (splenic PFC number, DTH reaction) parameters were measured. Treatment with the combination of Pb or Cd and DM did not result in a reduction of humoral (PFC) and cellular (DTH) immune responses, whereas treatment with the substances alone did result in immune suppression. This protecting effect can probably be attributed to an effect on the kinetics of the compounds tested rather than on the immune system itself. Further interactions were found in both combinations, DM-Cd and DM-Pb, in the body weight gain and in the relative liver weight; the DMPb combination also affected the relative thymus weight and the MCV value. These findings show that the immunotoxic effects of the investigated materials, including their detectability and health consequences, can be modified in case of combined exposure.