[Effects of mixed cypermethrin and methylparathion on endocrine hormone levels and immune functions in rats: II. Interaction].

Objective: To study interaction of mixed pesticides cypermethrin and methyl parathion on reproductive hormones, thyroid hormones, and immune functions in rats.

Methods: Eighty 2-month old Wistar rats (40 male and 40 female) were divided randomly by body weight into 8 groups. The dose 1/30 LD50 were chosen for the single or combined exposure representing respective doses of 0, cypermethrin 8.0 mg/kg bw, methylparathion 0.23 mg/kg bw, and 1/30 LD50 cypermethrin plus 1/30 LD50 methylparathion. The control group received vehicle solvent only. All groups were force-fed every two days for 30 days. Body weight gain and organ weights were determined. Serum levels of IgG and IgA, reproductive hormones [luteinizing hormone (LH), follicle stimulating hormone (FSH), estradiol (E2), and testosterone], as well as the thyroid hormones [triiodothyronine (T3), tetraiodothyronine (T4), and thyroid stimulating hormone (TSH) were measured using radioimmunoassay (RIA). In addition, two immunological parameters (rate of neutrophil phagocytosis, rate of lymphocyte transformation] were being measured in blood samples.

Results: The most of index indicated addictive interaction, while the effects on relative weights of ovaries and adrenals, IgA and rate of lymphocyte transformation were antagonistic. It was of interest that the effect on estradiol was synergistic interaction in female rats, whereas it was addictive interaction in male rats, whose estradiol level could be increased 64.64% by cypermethrin exposure.

Conclusion: Our results showed that exposure to cypermethrin and methyl parathion mixture at 1/30 LD50 dose had interaction on endocrine hormone levels, and immune functions in rats. Estradiol was very sensitive, the mixture can enhance estradiol level both in male and female rats.