Molecular and Histocytological Biomarkers - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 77

Körner et al. (2008), examining concomitantly the gene expression of the estrogen recep-
tor beta-1 (ERβ-1) and the glucocorticoid receptor (GR) in the liver of ethinylestradiol-
exposed fish, showed no treatment-related alterations. In line with observed constant bile
cortisol concentrations, their data did not indicate corresponding stress-related effects on
hepatic vitellogenin production. Jørgensen et al. (2001) investigated the responses to stress
in 2-(chlorophenyl)-2-(4-chlorphenyl)-1,1-dichloroethane ( o ʹ p -DDD) exposed (given a sin-
gle, oral dose of 75 mg o ʹ p -DDD kg -1 fish) and unexposed Arctic char Salvelinus alpinus . No
effects of o ʹ p -DDD were observed on post-stress hormone secretion (i.e., peak post-stress
plasma ACTH and cortisol levels).
According to Hontela (2000), at that time there was very little information available on
the cortisol status of fish chronically exposed to sublethal chemical stress in their medium,
despite the biological importance of cortisol that is implicated directly or indirectly (inter-
actions with other hormones such as thyroid hormones, reviewed by Peter 2011) in the
regulation of growth, reproduction (Milla et al. 2009), and resistance to disease, which are
vital functions, potentially impaired by chemicals. For instance, in the lake trout Salvelinus
namaycush , combinations of environmental contaminants (mercuric chloride or Aroclor
1254) and cortisol interact to produce a greater toxicity than that of the environmental con-
taminant alone. Hence, stressors that lead to increased cortisol production may increase
the toxicity of mercury and Aroclor 1254 to lake trout thymocytes (Miller et al. 2002). Pre-
exposure to copper and atrazine resulted in the abolition of an acute cortisol post-stress
in the freshwater fish Prochilodus lineatus (Nascimento et al. 2012) and the rainbow trout
Oncorhynchus mykiss (Tellis et al. 2012) exposed to other stressors (air exposure or confine-
ment). In trout, there was no Cu accumulation in the hypothalamus-pituitary-interrenal
axis (HPI axis) suggesting this was not a direct toxic effect of Cu on the cortisol regula-
tory pathway and the ability of the fish to maintain ion and carbohydrate homeostasis
was maintained. Tellis et al. (2012) suggest that this effect on cortisol may be a strategy to
reduce costs during the chronic stress of Cu exposure, and not endocrine disruption as a
result of toxic injury. However, Nascimento et al. (2012) suggest that P. lineatus suffering an
impaired cortisol stress response may not be able to respond to any additional stressors.
The response of cortisol has been used by Hontela's (2000) team to evaluate the func-
tional integrity of the hypothalamo-hypophysio-interrenal axis in fish living in contami-
nated environments. Cortisol failure (with addition of low levels of plasma thyroxin) was
detected in mature males and females and immature yellow perch Perca flavescens and
northern pike Esox lucius in the Saint Lawrence River by comparing reference and contam-
inated (PCBs, PAHs, Cd, Hg) sites. Cortisol depletion was observed by the same team in
both species in a river impacted by a kraft paper mill. Lockhart et al. (1972 in Hontela 2000)
reported lower levels of plasma cortisol and glucose in pike originating from a mercury-
contaminated lake compared to fish from a reference lake. Cortisol and glucose levels
appeared as responsive stress biomarkers in a field study using the barbel ( Barbus bocagei )
and the carp ( Cyprinus carpio ) collected in the Tagus River (Iberian peninsula) at a refer-
ence site and nine sampling sites selected on the basis of whether various human activities
and hydrographic characteristics were present (Carballo et al. 2005).
Less information is available for cortisol in other taxa. However, the review by Letcher et
al. (2010) on effect assessment of persistent organohalogen contaminants in arctic wildlife
and fish reports that organochlorine (OC) pesticides combined with PCBs and their inter-
actions could account for more than 25% of the variation in plasma cortisol concentrations
in polar bears. Cortisol concentration in East Greenland polar bears was found at signifi-
cantly higher concentrations in historical hair samples (1892-1927; n = 8) relative to recent
ones (1988-2009; n = 88). In addition, there was a linear time trend in cortisol concentration