Comparative subacute toxicity of dietary diazinon in the male and female rat

Male and female rats were fed a semipurified diet containing either 0,2 or 25 ppm diazinon for varying times. At appropriate times, animals were bled from the orbital sinus to facilitate measurement of plasma cholinesterase and erythrocyte acetylcholinesterase activities. Additional animals were sacrificed to enable determination of brain acetylcholinesterase activity. General nutritional evaluations included measurement of body weight gains and feed consumption during the growing period. Feeding diazinon at the levels employed produced no visible toxic manifestations. Body weight gains and feed consumption were comparable among control and treated groups during all studies. Feeding 25 ppm diazinon for 30 days produced more significant reduction of cholinesterase activity in plasma (by 22–30%) and brain (by 5–9%) among treated females compared to corresponding males. Erythrocyte acetylcholinesterase activity was significantly more depressed (by 13–17%) in treated females relative to appropriate males at Days 21–28 of the feeding trial. At no time was cholinesterase activity in any tissue assayed more significantly reduced among treated males than females. Feeding 2 ppm diazinon for 7 days failed to modify erythrocyte acetylcholinesterase activity among both sexes relative to controls. Plasma cholinesterase activities of treated males were not significantly different from control values, whereas, treated females showed significant depression (by 29%) of plasma enzyme activity. This latter finding is of interest since 2 ppm is the “no effect” level of diazinon for the rat established by the FAO/WHO on the basis of studies which focused on the male sex. The results indicate the female rat to be more sensitive to the toxicity of dietary diazinon compared to the male.