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Abstract
This study investigated the effect of different photoperiods on acetaminophen-induced hepatotoxicity in rats. Twenty four adult male rats (average weight = 160±7g) were conditioned to different photoperiod regimens for 6 weeks. At the end of the 6-week period, rats exposed to normal, short and long photoperiods received oral acetaminophen (2g/kg body weight) while in the control group, exposed to normal photoperiod, received oral saline. Rats were sacrificed 24 h after acetaminophen administration by cervical dislocation and blood was collected by cardiac puncture for the estimation of liver enzymes activities. Liver tissues were excised and homogenized for estimation of liver malondialdehyde (MDA) concentration. Elevation of serum levels of alanine and aspartate transaminases and alkaline phosphatase caused by acetaminophen intoxication were not affected in rats subjected to long photoperiod while these parameters were significantly (P<0.05) reduced in rats subjected to short photoperiod. However, alteration of photoperiod resulted in significantly (P<0.05) lower serum gamma glutamate transpeptidase and total protein in acetaminophentreated rats. All groups of rats had similar serum albumin while serum malondialdehyde concentration was significantly lower in rats subjected to short photoperiod. This study revealed the protective effects of short photoperiod against acetaminophen-induced hepatotoxicity and lipid peroxidation in rats. Key words : Acetaminophen, photoperiod, lipid peroxidation, Hepatotoxicity
Highlights
Studies have shown that short day lengths generally enhance many types of immune responses in the laboratory animals (Nelson, 2004; Olayaki et al, 2008)
Effects of photoperiods on serum levels of liver function parameters in acetaminophentreated rats: Administration of acetaminophen resulted in marked elevation of serum levels of AST (496%, P
Exposure to long photoperiod (16:8, light:dark hr) produced no significant effect on serum levels of AST, ALT and ALP but inhibited increased serum levels of GGT caused by acetaminophen administration by 26% (P
Summary
Studies have shown that short day lengths generally enhance many types of immune responses in the laboratory animals (Nelson, 2004; Olayaki et al, 2008). Increased cellmediated immune responses including lymphocyte proliferation to mitogens, delayed-type hypersensitivity responses and overall numbers of circulating immune cells have been reported as a consequence of exposure to short day length (Blom et al, 1994; Demas and Nelson, 1996; Demas and Nelson, 1998; Bilbo et al, 2002). A hormone produced by a wide range of organism including animals, plants and microbes, has been reported for its antiinflammatory and immune enhancing actions in laboratory animals (Maestroni et al, 1987; Guerrero and Reiter, 2002). Previous studies have shown that melatonin exhibited hepatoprotective effect by reducing the generation of reactive oxygen species and lipid peroxidation (Kanno et al, 2006). Pineal melatonin production exhibits a circadian rhythm, with a low level during daytime and high levels during night (Claustrat et al, 2005)
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