SYMPOSIUM on Marine Accidental Oil Spills
Effects of different polycyclic aromatic hydrocarbons in the
teleostean fish rainbow trout in relation to sexual development
and response to stress
Manuel GESTO, Adrián TINTOS, Jesús M. MÍGUEZ and José L. SOENGAS.
Laboratorio de fisioloxía animal, Facultade de Bioloxía, Edificio de Ciencias Experimentáis, Universidade
de Vigo / 36310, Vigo, SPAIN
ABSTRACT
Polycyclic aromatic hydrocarbons (PAHs) are the main toxic and persistent compounds
present in most crude oils. As a result of the continuous incomes from submarine, terrestrial and
atmospheric sources to the sea PAHs are now ubiquitous contaminants of aquatic ecosystems.
High molecular weight-PAHs (specially with 4 or more condensed rings) are very toxic at
multiple levels. Smaller ones have minor intrinsic toxicity but their biodisponibility is much
higher, as a result of their higher solubility in water. PAHs have many deleterious effects on
aquatic organisms. Among them, their capacity to disrupt endocrine systems is one of the most
dangerous from the point of view of organism populations, since reproduction could be
compromised when any reproductive parameter is affected. PAHs mechanisms of action distinct
of those mediated by the aryl hydrocarbon receptor (AhR) are not well understood.
In our studies we evaluated the capacity of different PAHs to alter different steroid
hormones, like 17β-estradiol or cortisol. Furthermore, we assessed simultaneously, several
parameters of energy metabolism and brain monoaminergic neurotransmission systems.
Naphthalene altered plasma levels of 17β-estradiol (a sexual steroid) and cortisol (an interrenal
steroid) as well as liver intermediary metabolism and brain monoaminergic systems in juvenile
female rainbow trout. Several studies were conducted with this PAH to investigate whether or
not these alterations were dependent on vitellogenic stage of the fish and if they could interfere
with trout reproduction. In subsequent experiments we evaluated the effects of higher molecular
weight PAHs. Thus, like naphthalene, β-naphthoflavone and benzo(a)pyrene altered cortisol,
liver intermediary metabolism and brain noradrenergic, dopaminergic and serotonergic systems
of rainbow trout. In addition, the capacity of all three PAHs to disrupt the endocrine response of
the fish to acute or prolonged stress situations was tested.
Modes of action of low and high molecular weight PAHs within fish organism seem to be not
identical. While naphthalene (low MW) disrupts both 17β-estradiol and cortisol systems, βnaphthoflavone and benzo(a)pyrene (high MW) only affect cortisol levels. The normal elevation
of plasmatic levels of cortisol when fish are exposed to an acute stress stimulus further
increased when fish were treated with all the PAHs tested. However, when stress stimuli are
prolonged, β-naphthoflavone and benzo(a)pyrene-treated fish were not able to mantain high
levels of cortisol, suggesting a toxic action of this PAHs, not elicited by naphthalene. Changes in
liver metabolism are similar for both low and high molecular weight PAHs: processes leading to
higher plasmatic levels of glucose, like glycogenolysis and gluconeogenesis, are enhanced,
suggesting a greater energetic demand that could serve to support detoxification processes.
These changes were also dependent on sexual maturation stage of fish. With respect to brain
monoaminergic systems, changes in noradrenergic, dopaminergic and serotonergic activity
were in general very dependent on neurotransmitter, brain region and PAH used. They were
also inconsistent over exposure times to the PAHs and a nonspecific mechanism of action as
nonpolar narcosis is likely to be involved in these changes.
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