Weight gain associated with chronic exposure to chlorpyrifos in rats

This work exposed rats to low levels of the organophosphate insecticide chlorpyrifos and monitored for toxic effects, including weight gain.

Rats received either a subcutaneous injection of chlorpyrifos, 5 mg/kg/day, or an equal volume of vehicle daily for 4 months. Subjects were observed for 30 minutes after injection for signs of acute toxicity. Body weights were recorded at baseline, 2 months, 3 months, and 4 months. At the end of the experiment, the weights of hearts, medial lobe of the livers, peri-nephric fat pads, and gastrocnemius muscles were recorded. Effects of chlorpyrifos on adipocyte differentiation in culture were studied. Results were compared using RMANOVA.

No signs of acute cholinergic toxicity were observed after injections in any subject. Rats in the 5 mg/kg group were significantly heavier than those in the control group by 2 months (335.7 +/- 16.7 g vs. 318.6 +/- 15.8 g; p = 0.034). This difference increased at 3 months (350.1 +/- 16.4 g vs. 322.3 +/- 21.3 g p = 0.006) and 4 months (374.4 +/- 22.2 g vs. 340.2 +/- 25.2 g p = 0.006). At 4 months, the weights of the perinephric fat pads were significantly increased in the chlorpyrifos group relative to controls (2.867 + 0.516 vs. 1.130 + 0.171, p = 0.0039). The two groups showed no weight differences between hearts, livers, and gastrocnemius muscles. Chlorpyrifos did not affect adipocyte differentiation in tissue culture.

Chronic exposure to chlorpyrifos at 5 mg/kg/day caused an increase in rat body weight when compared to controls. This increase was in adipose tissue. Chlorpyrifos did not induce differentiation of adipocytes in culture.