Circadian susceptibility rhythms to some organophosphate compounds in the rat.

LD50 values after i.p. doses of phenitrotion (PH), dichlorvos (D) and methyl parathion (MP) were established at 0600, 1200, 1800 and 0000 and plasma corticosterone was determined in male rats. The PH toxicity was significantly higher at 0600 than at 1800. Moreover, there was a significant difference between the PH toxicity at 1200 (lower) and 0000 (higher). The D toxicity differed significantly only between 1200 (higher). There was however a lack of circadian susceptibility, rhythm to MP. The results differ according to the metabolic fate and the solubility of the tested compounds.