To study interaction and dose-related effects of mixed cypermethrin and methyl parathion on endocrine and immune functions, 120 Wistar rats were divided randomly into six groups of ten male and ten female rats, respectively, at the age of 2 months. All groups were force-fed every 2 days for 30 days with cypermethrin 0.0, 8.0, 0.0, 8.0, 1.8, 0.4 mg/kg bw and methyl parathion 0.0, 0.0, 0.23, 0.23, 0.0518, 0.0115 mg/kg bw. Controls received vehicle solvent only. Body weight gain and organ weights were measured. Serum or blood were used to test luteinizing hormone, follicle stimulating hormone, estradiol (E(2)), testosterone, thyroid hormones (T(3), T(4), TSH), IgG, IgA, rate of neutrophil phagocytosis and of lymphocyte transformation. The effects on relative weights of ovaries and adrenals, IgA and rate of lymphocyte transformation were antagonistic interaction; the effect on estradiol was synergistic in female, whereas addictive in male rats; and the other indices indicated addictive interaction. Organ weights were similar in exposed and control animals except for adrenal (heavier in exposed rats, P<0.01). Serum levels of FSH and estradiol were higher in exposed groups than in controls (P<0.01). IgG levels were lower in exposed rats than in controls (P<0.01), and IgA levels were higher in exposed females than in controls (P<0.01). Lymphocyte transformation rates were lower (P<0.01) and neutrophil phagocytosis rates were higher (P<0.01) in exposed rats than in controls. Our results showed that exposure to low-dose mixtures of cypermethrin and methyl parathion may affect hormone levels (especially estradiol) and immune function in rats, and the NOAELs of combined compounds were located at 1/600 LD(50).
