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APRIL 30, 2007
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Donna Krupa
Office: (301) 634-7209
Cell: (703) 967-2751
dkrupa@the-aps.org
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Saturday April 28
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Hearts Of Male And Female
Rainbow Trout Are Different
Female
rainbow trout prefer carbohydrates and tolerate lower oxygen levels better
than males
WASHINGTON – The heart is one of the most energy
demanding organs of the human body. Its failure to function properly
accounts for 600,000 deaths each year. Similarly, the rainbow trout, native
to the Pacific Northwest and beloved as a sport- and food fish, requires
dynamic and sustained cardiac function to maintain its health and swimming
activity.
Previous studies of trout cardiac performance and
energy metabolism have been conducted under hypoxic (oxygen shortage)
conditions, but gender was not specifically examined. Nor were comparisons
made between male and female fish (the largest group of vertebrates) made.
There is a growing appreciation of significant sex differences in cardiac
characteristics and function in adult humans. A new research study begins to
close the gender gap in fishes, and finds that sex differences in cardiac
performance and metabolism exist in rainbow trout. These differences occur
at a young age and are only realized when the trout heart is contracting and
not under resting conditions.
The study is entitled Sex Differences in Cardiac
Glucose Metabolism and Function in Immature Rainbow Trout (Oncorhynchus
mykiss). It was conducted by Pavan K. Battiprolu, Adam C. Goddard and
Kenneth J. Rodnick, all of the Department of Biological Sciences, Idaho
State University, Pocatello, Idaho. Dr. Rodnick’s laboratory is presenting
the team’s findings at the 120th American Physiological Society (APS;
www.the-APS.org) annual meeting, which is being held as part of the
Experimental Biology (EB ’07) conference. More than 12,000 scientific
researchers will attend the gathering being held April 28-May 2, 2007 at the
Washington, DC Convention Center.
The Study
The researchers examined if two regulatory molecules
found in the fish heart -- citrate (an acid which inhibits the glycolytic
metabolic pathway) and pyruvate dehydrogenase (PDH), the enzyme allowing
carbohydrates to be oxidized -- differ between the sexes. The researchers
hypothesized that male hearts would have higher citrate levels and females
would benefit more from the stimulation of PDH than males.
The study also sought to determine if sodium cyanide (NaCN)
-- an inhibitor of oxidative metabolism – decreases activity of the
glycolytic pathway and cardiac performance in both sexes, and if males
possess a larger outermost (epicardial) layer of the ventricle vs. the inner
endocardium layer. The trout heart is a composite organ and layer
distinction is important because the epicardium, much like the human heart,
receives oxygenated blood via the coronary circulation. Conversely, the
endocardium is supplied by only deoxygenated blood returning from the rest
of the body. Not surprisingly, the authors expect there to be corresponding
layer differences in energy production and function.
Methodology
Uniform ventricle strips
or transverse rings were cut from 10-12 month old, hatchery raised,
sexually-immature male and female rainbow trout. Each strip was prepared in
one of two ways: (1) incubated without stimulation (i.e., ventricle strips
were incubated in a respiration cell containing an oxygenated buffer
solution with glucose as the energy substrate). Oxygen consumption was
measured using a calibrated oxygen electrode and data acquisition system; or
(2) electrically-paced (i.e., ventricle strips were electrically-stimulated
at physiological rates and temperature in tissue baths containing buffer,
with (a) glucose and (b) glucose + DCA (dichloroacetate, an activator of PDH
and a therapeutic drug used to treat human heart disease and cancer), or (c)
glucose + NaCN under oxygenated and hypoxic conditions.
The researchers measured
several indices of contractile performance (resting tension, twitch force,
post-rest potentiation and other variables. Frozen samples of ventricle
tissue were homogenized and assayed for citrate concentration. Ventricle
rings were processed, sectioned and stained. Light microscopy was used to
capture images of ventricle layers and analyzed for layer cross-sectional
areas. Lactate concentration and net lactate release from cardiac tissue
was also examined.
Results
The researchers found:
-
ventricle strips from males and females had similar rates of oxygen
consumption and lactate release under resting conditions;
-
the inhibition of oxidative metabolism with NaCN lowered cardiac
performance dramatically, and elevated resting tension and lactate
release in both males and females;
-
under stimulated conditions with DCA vs. controls, female
ventricle strips selectively demonstrated better performance and reduced
lactate release;
-
force production during reoxygenation – after
a hypoxic insult -- significantly improved in males receiving DCA, but
not females;
-
male ventricle tissue had 2.5-fold
higher citrate concentrations than
females; and;
-
males had a proportionately larger epicardium to endocardium ratio
compared with females with similar size hearts.
Summary and Conclusions
This study expands upon
previous findings that sex differences in cardiac performance and metabolism
exist in fish in general, and have now been found to occur in rainbow trout
in particular. Moreover, the differences are only realized during working
conditions and involve stimulation or inhibition of the glycolytic pathway
and carbohydrate oxidation. Ultimately, sex differences in cardiac energy
metabolism and function may help define habitat suitability, swimming
capabilities and health status of wild and hatchery-reared rainbow trout,
and human heart disease, sex-specific treatment.
***
The research was funded by the NIH (grant # P20 RR16454
from the BRIN-INBRE Program of the National Center for Research Resources)
and NSF (award # IOB-517669).
The
American Physiological Society (APS) has been an integral part of the
scientific discovery process since it was established in 1887. Physiology
is the study of how molecules, cells, tissues and organs function to create
health or disease.
# # #
NOTE TO EDITORS: The APS annual meeting is part
of the Experimental Biology 2007 (EB ’07) gathering and will be held April
28-May 2, 2007 at the Washington, DC Convention Center. To schedule an
interview with Dr. Rodnick, please contact Donna Krupa at 301.634.7209
(direct dial), 703.967.2751 (cell) or
DKrupa@the-APS.org.
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