Chlorpyrifos and parathion effects on enzyme activities in fingerling channel catfish, Ictalurus punctatus: Interactions with DEF (S,S,S-tributyl phosphorotrithioate) and Aroclor 1254

Channel catfish fingerlings were exposed to various xenobiotics in experiments to evaluate effects on enzyme activity.; In the first study, brain, gill, liver, muscle, and plasma were assayed for acetylcholinesterase (AChE) inhibition and gill, liver, and plasma were assayed for aliesterase (ALiE) inhibition in vitro by DEF and oxons of chlorpyrifos (Cpxn) and parathion (Pxn). DEF (1 mM) inhibited AChE activity {dollar}<{dollar}15% in all tissues. AChE I{dollar}sb{lcub}50{rcub}{dollar} values for Cpxn were 28-33 nM, and for Pxn were 446-577 nM. ALiE I{dollar}sb{lcub}50{rcub}{dollar} values for Cpxn were 0.1-0.2 nM, for DEF were 24-163 nM, and for Pxn were 6-46 nM.; In the second study, fish were exposed to chlorpyrifos (Cp), parathion (Pth), DEF, and combinations of the phosphorothionates and DEF for 4 h followed by a 388 h recovery period. AChE inhibition following Cp and Pth exposures was rapid. Cp led to more persistent inhibition than Pth. DEF treated fish had low inhibition in brain and muscle, and high inhibition in gill, liver, and plasma. In vitro and in vivo results suggest that DEF's disposition and mode of action are different than those of Cp or Pth. ALiE activities demonstrated that exposure to DEF or combination treatments resulted in persistent, high inhibition. Greater AChE inhibition in combination treatments was not evident suggesting that ALiEs do not serve to protect AChE, even though ALiEs are inherently more sensitive to inhibition.; In the third study, fish were exposed for 20 h to piperonyl butoxide (PBO) followed by a 4 h exposure to DEF. AChE activities were determined at 0 and 12 h after the exposure period. Inhibition of brain, plasma, and liver AChE activity by DEF was antagonized by PBO; muscle AChE was not inhibited by DEF. PBO did not antagonize the inhibition of liver or plasma ALiE by DEF. These results suggest that PBO retards the formation of the metabolite(s) of DEF that inhibit AChE.; In the fourth study, fish were injected (IP) with 100 mg Aroclor 1254/kg body wt and sacrificed at 96 h. Microsomal cytochrome P450-mediated deethylation of 7-ethoxyresorufin was induced; however, effects on desulfuration or dearylation of Cp and Pth were not evident. Results indicate that Aroclor 1254 does not appreciably induce the isozymes of cytochrome P450 responsible for desulfuration and dearylation at the treatment rate tested.