Effects of dichlorvos on blood cholinesterase activities of cattle.

Inhibitory effects of dichlorvos (2,2-dichlorovinyl dimethyl phosphate, DDVP) [corrected] on erythrocyte acetylcholinesterase (AChE) and plasma cholinesterase (ChE) activities of steers were characterized after treatments in vitro and in vivo (cutaneous application). The rates of in vitro inhibition were markedly influenced by DDVP concentration and incubation time. The activities of inhibited enzymes failed to reactivate spontaneously and had little response to treatment with 2-pyridine aldoxime methiodide (2-PAM). After gel-filtration chromatography, however, the inhibited enzymes had remarkable spontaneous reactivation and reactivation by 2-PAM treatment, indicating interference of excess unreacted DDVP in the reactivation process. Repeated cutaneous applications of a DDVP-containing livestock spray caused marked and characteristic decreases of AChE and ChE activities in blood of treated steers; however, the effects were transient because activities of both enzymes regenerated gradually. The nature of these in vivo trends suggests that spontaneous and de novo synthetic mechanisms could be responsible for complete recovery of both enzyme activities.