February 15-18, 2009 Washington State Convention Center Seattle ...

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A PRELIMINARY ASSESSMENT OF PROTEIN SYNTHESIS USING DEUTERATED WATER:
A NOVEL APPROACH TO CHARACTERIZE GROWTH OF CHANNEL CATFISH Ictalurus
punctatus
Camilo Pohlenz*, Heath Gasier, Michael Wiggs, Alejandro Buentello, Stephen Previs, James Fluckey and Delbert
Gatlin III
Texas A&M University System
College Station, TX 77840-2258 USA
cpohlenz@tamu.edu
A thorough understanding of protein synthesis (PS) in the skeletal muscle of fish is needed to improve the efficiency of aquaculture
production. In fish, muscle accounts for over 50% of total mass of most species, and is composed mainly of protein.
Traditionally, PS in fish has been assessed with a procedure known as the “flooding dose”. However, concerns about the
suitability of this method have surfaced as a result of sharp variations obtained for whole–body PS estimates. These variations
likely result from the brevity of treatment and nutritional state of the animal at the time of measurement. Deuterium oxide
( 2 H 2 O) is a versatile stable isotope tracer that makes possible the study of bio–molecule dynamics with minimal disturbance
to the living organism, and permits long–term investigations which yield integrative measures of PS. Therefore, the specific
objective of this study was to evaluate fractional synthetic rates (FSR) of muscle PS in juvenile channel catfish. To this end,
the incorporation of 2 H from 2 H 2 O administered in–vivo into L–alanine was used to compute FSR.
A preliminary experiment to evaluate the equilibration of plasma H 2 O with 2 H 2 O used 24 fish (~65 ± 1.2 g each) in a 30–L
aquarium. 2 H 2 O was added to the water at a 4.0% concentration. Samples of six randomly selected fish were taken at 0, 4,
8 and 24 h for extraction of blood from the caudal vein and muscle from the left epaxial myomere. Separated plasma and
dissected muscle samples were rapidly stored frozen at –80 C, until further analysis. In a second experiment, the effects of
dietary arginine (Arg) on muscle FSR were evaluated. After a 6–week feeding period with two different levels of L–Arg•HCl
(0.5 and 4.0% of diet), 2 H 2 O was added to the aquarium water and six fish/diet were sampled at 24 h, as described above. Gas
chromatography/mass spectrometry was used to assess the 2 H–labeling of plasma water and muscle protein.
Table 1 indicates that 2 H equilibrated in catfish plasma within 1 h, and remained stable for ~ 24 h. There was a continuous
increase in the 2 H–labeling of muscle protein. FSR was only calculated from the 24 h samples. No significant differences
(P > 0.05) were observed between FSR of fish fed different levels of Arg. Taken together these results indicate that the assessment
of PS over an extended period of time is easily attained in catfish using deuterated water. Some advantages of using of
2 H2 O to evaluate PS are that it is a non–invasive and relatively inexpensive method, accounts for the influence of feeding; and,
the ease of administration makes it a practical assessment option.