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International Journal of Marine Science 2014, Vol.4, No.44, 1-14
http://ijms.biopublisher.ca
8
protein peptide fragments is a rapidly growing field of
research. Studies suggest that various biologically
active peptides can result in favorable or negative
outcomes on organism, and the role of biologically
active short sequence peptides as potential agents
through the modulation of age-, sex- and pathologies
-dependent biochemical pathways is very important
(Grune, 2000; Karyakina and Belova, 2004). Thus,
oligopeptides concentration in animal tissues serve be
biomarkers of physiological status.
In our study oligopeptides concentration in the liver of
examined elasmobranchs was significantly higher in
buckler skate compared with dogfish and stringray. In
the serum the greatest value was indicated in dogfish,
while no significant differences shown in red blood
cells of examined fish species. We suggest the
observed difference could be explained by the
specificity of metabolic rate of the species. High level
of oligopeptides in shark serum could be associated
with its active swimming and feeding behavior,
transport and excretory function of blood serum, while
ray and skate are more sluggish and their metabolic
rate is slower.
Marine elasmobranchs are osmoconforming hypoionic
regulators, with extracellular fluids containing lower
ionic levels than the surrounding marine water. Yet,
the plasma osmolality is hyperosmotic to the external
medium due to the retention of urea. (Ip et al., 2009).
Taking this into account, we propose that
oligopeptides in elasmobranch serum may be involved
in the regulation of osmolality, together with urea and
trimethylamine oxide (TMO) (Filho and Boveris,
1993; Harms et al., 2002; Metcall and Gemmell, 2005;
Lopez-Cruz et al., 2010).
No correlations were observed between oligopeptides
level in the serum, red blood cells and in the liver,
indicating
they
fluctuate
independently
in
elasmobranchs. However, data pertaining to
oligopeptide concentrations in fish tissues are very
limited, and further investigations are needed to
understand the relationship of interspecies differences
to the ecology and life history of the species in
question.
Antioxidant defense of the organism include several
enzymes: SOD protects against oxidative damage by
catalyzing the reaction of dismutation of the
superoxide anion to H
2
O
2
, which degrades by CAT to
H
2
O. PER includes peroxide-degrading enzymes both
specific and nonspecific, which reduce both hydrogen
peroxide and hydroperoxides. GR maintains a ratio of
GSH/GSSG under oxidative stress; it is a major
regulatory enzyme that regenerates GSH from GSSG
(Livingstone, 2001; Lesser, 2006). Alterations in the
antioxidant enzyme activities of aquatic animals in
response to environmental changes are used to
indicate the potential for more severe hazards.
In our study antioxidant enzyme activities in the liver
of the ray and skate were higher than in dogfish.
Given the sluggish nature of skates and rays, these
results contradict several other studies demonstrating
that antioxidant levels in fish species depended on
metabolic oxygen consumption or swimming activity
(Filho et al., 1993; Sole et al., 2009; Lopez-Cruz et al.,
2010). Furthermore, antioxidant enzyme activities
differ between tissue type and function (Filho and
Boveris, 1993; Filho et al., 1993; Rudneva, 2012;
Velez-Alavez et al., 2013).
Our findings show a different trend of antioxidant
levels in elasmobranch liver and red blood cells. In
dogfish blood SOD and CAT activities were
significantly lower than in skates, while PER and GR
level demonstrated the opposite trend. No correlations
between antioxidant enzyme activities in liver and red
blood cells of tested elasmobranchs were observed
with the exception of strong positive correlation
between hepatic and blood CAT activity (r=0.93). We
therefore conclude that antioxidant enzyme levels vary
independently in the liver and in red blood cells of
tested elasmobranchs. It could be associated with
different functions of blood and liver.
Like the increased concentrations of oligopeptides in
the dogfish, the increased concentration of PER and
GR in shark blood compared with skate/rays may be
associated with the increased swimming activity of the
dogfish. However, in our previous study no
differences in glutathione-S-transferase (GST, the
phase II biotransformation enzyme) activity were
observed between examined Black Sea ray and skate.
Because GST involves in antioxidant defense of the
organism also, and taking into account the
peculiarities of metabolic pathways of elasmobranchs
we proposed the presence of specific GST activity in
their tissues (Rudneva et al., 2010a, b).