In the present study, electron paramagnetic resonance coupled with spin-trapping technique was used, with alpha-
phenyl-N-tert-butylnitrone (PBN) as a spin-trapping agent, to investigate
free radical generation in freshwater fish with acute
2,4-dichlorophenol (2,4-DCP)
poisoning. The PBN-radical adducts were detected in fish liver samples following treatments of 2,4-DCP (0.025, 0.05, 0.5, 5, or 25 mg/kg) 24 h after intraperitoneal (i.p.) injection and 2,4-DCP (0.5 mg/kg) at 2, 4, 8, 24, or 72 h after i.p. injection in Carassius auratus. The hyperfine splitting constants for the PBN-radical adducts are aN = 13.7 G, aH = 1.8 G, and g = 2.0058, which is consistent with those of PBN/
hydroxyl radical (*
OH). The results indicate that the
hydroxyl radical is probably produced during acute intoxication of 2,4-DCP. The relative similarity in the kinetics (from 2 to 72 h) of
superoxide dismutase activity induction and *
OH generation implies that the generation of *
OH possibly depends on the
superoxide anion (O2*-).
Superoxide anion (O2*-) might be the precursor radical undergoing the Haber-Weiss reaction to form *
OH. Possible pathways for radical chain reactions in the formation of the
hydroxyl radical in vivo after 2,4-DCP administration are proposed. Other parameters with respect to
antioxidant defense (e.g.,
superoxide dismutase and
catalase) and oxidative damage (lipid peroxidation level) indicate that the fish were subjected to oxidative stress induced by 2,4-DCP and that the mechanisms of oxidative stress possibly involve the in vivo stimulation of
hydroxyl radical formation.