[Effects of mixed cypermethrin and methylparathion on endocrine hormone levels and immune functions in rats: I. Dose-response relationship].

Objective: To study dose-response relationship effects of mixed cypermethrin and methyl parathion on reproductive hormones, thyroid hormones, and immune functions in rats.

Methods: Eighty 2-month old Wistar rats (40 males and 40 females) were divided randomly by bodyweight into 4 groups. Four doses (0, 1/600 LD50, 1/135 LD50 and 1/30 LD50) were chosen for the combined exposure representing respective doses of cypermethrin 0, 0.4, 1.8 and 8.0 mg/kg body weight and of methylparathion 0, 0.0115, 0.0518 and 0.2300 mg/kg body weight. The control group received vehicle solvent only. All groups were force-fed every two days for 30 days with these dose combinations. 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 body weight gains were similar in all 4 groups. The weights of adrenal glands in exposed rats were heavier than those in control (P < 0.05). Serum FSH and E2 levels in exposed rats were higher than those in the control group (P < 0.01). Serum TSH levels were proportionally increasing with higher pesticide doses (r(s) = 0.329, P < 0.01). Lymphocyte transformation rates in all exposed animals were lower than that of the control group (P < 0.01). To the contrary, rates of neutrophil phagocytosis in all exposure groups were higher than those of the control group (P < 0.01). Furthermore, serum IgG levels of all exposed animals were lower than that of the control (P < 0.01) and serum IgA levels in exposed females were higher than that of the control (P < 0.01). Dose-response relationships for these changes were significant (rank correlation statistics P < 0.05 or < 0.01).

Conclusion: Our results showed that exposure to different mixtures of cypermethrin and methyl parathion disrupted the endocrine hormone levels, and immune functions in rats.