Time course of inhibition of acetylcholinesterase and aliesterases following parathion and paraoxon exposures in rats

Detoxication of paraoxon by rat liver homogenate and serum carboxylesterases and A-esterases*

“…They suggested that these nonspecific binding sites might be nonvital esterases such as CbxE and pseudocholinesterases. Both in vitro and in vivo studies have shown that rat hepatic CbxE are more sensitive to inhibition by some oxons, including PO, than is rat brain AChE (6,7). In the present in vitro study, more than 50% of the total CbxE detoxication capacity was reached in 5 seconds, and the saturation of CbxE occurred in 3 minutes (Figure 1), suggesting that PO may be readily destroyed by CbxE as soon as it is generated in the liver because of the potency of PO as a CbxE inhibitor (IC 50 of 1.3 nM) (6).…”

Effect of Organophosphorus Compound Intoxication on Auditory Brainstem Response in Mini Pigs

“…Champers and Chambers [11] reported that a paraox on intoxication given at a dosage of 1.75 mg/kg to rats causes and maximal inhibition of the brain ChE of 90% and that severe signs characteristic of anticholinesterase poisoning are seen after 60 min.…”

The effect of high and low dosages of paraoxon in β-naphthoflavone-treated rats

“…These dosages were selected to yield about 25 and 60% inhibition of brain AChE for the low and the high dosage, respectively, at 1 hour post administration. Intravenous administration was used to avoid P‫ס‬O's sequestration by the residual oil in the peritoneal cavity, as may have been the case with ip administration in the earlier study (8). All appropriate naive, vehicle, and pretreatment controls were also studied.…”

“…The AChE assay was performed in all brain parts by a modification of the Ellman et al (11) technique using acetylthiocholine as the substrate and 5,5Ј-dithiobis(nitrobenzoic acid) as the chromogen, as described previously (8). Protein concentration was quantified by the method of Lowry et al (12) using bovine serum albumin as the standard.…”

“…Previous studies had indicated that BNF pretreatment decreased hepatic aliesterase activity and yielded a decreased amount of hepatic aliesterase inhibition following intraperitoneal (i.p.) treatment with an organophosphate (8); however, the presence of the oil vehicle complicated interpretation of the results. Additionally, hepatic aliesterases from BNF-treated rats had different patterns of substrate specificity and in vitro P‫ס‬O inhibition patterns compared with aliesterases from controls (9).…”