Objective—To determine the growth-related changes
in metabolic and anatomic properties in equine muscle
fiber type, including hybrid fibers identified with
Animals—24 2-, 6-, 12-, and 24-month-old female
Procedure—Samples were obtained from the gluteus
medius muscle of all horses. Expression of
myosin heavy chain (MHC) isoforms MHC-I, -IIa, -IIb,
and -IIx in each muscle fiber was detected by use of
4 primary monoclonal antibodies: BA-D5, SC-71, BFF3,
and BF-35, respectively. Five muscle fiber types
(types I, I/IIA, IIA, IIA/IIX, and IIX) were immunohistochemically
identified. The area and activity of succinic
dehydrogenase (SDH) in each fiber type were determined
by use of quantitative histochemical staining
and image analysis.
Results—Although the proportion of type I and IIX
fibers did not change with age, the proportion of type
IIA and IIA/IIX fibers significantly increased and
decreased, respectively, from 2 months to 24 months
of age. The increase in proportion of type IIA fibers
with growth may have been attributable to muscle
fiber-type transition from type IIA/IIX fibers but not
from type IIX fibers. Values for SDH activity and fiber
area in hybrid fiber types were intermediate to those
for their respective pure phenotypes.
Conclusions and Clinical Relevance—Hybrid fibers
have an important role for determining the proportion
of muscle fiber type in horses < 24 months old, and
the metabolic and anatomic properties of the hybrid
fibers are well coordinated, as in mature horses.
(Am J Vet Res 2005;66:401–405)
Objective—To determine the effect of growth and
training on metabolic properties in muscle fibers of
the gluteus medius muscle in adolescent
Animals—Twenty 2-year-old Thoroughbreds.
Procedure—Horses were randomly assigned to 2
groups. Horses in the training group were trained for
16 weeks, and control horses were kept on pasture
without training. Samples were obtained by use of a
needle-biopsy technique from the middle gluteus
muscle of each horse before and after the training
period. Composition and oxidative enzyme (succinic
dehydrogenase [SDH]) activity of each fiber type were
determined by use of quantitative histochemical
staining procedures. Whole-muscle activity of SDH
and glycolytic enzyme (phosphofructokinase) as well
as myosin heavy-chain isoforms were analyzed biochemically
and electrophoretically, respectively.
Results—The SDH activity of type-I and -IIA fibers
increased during growth, whereas whole-muscle
activity was unchanged. Percentage of type-IIX/B
muscle fibers decreased during training, whereas that
of myosin heavy-chain IIa increased. The SDH activity
of each fiber type as well as whole-muscle SDH activity
increased during training. An especially noticeable
increase in SDH activity was found in type-IIX/B fibers.
Conclusions and Clinical Relevance—Changes in
muscle fibers of adolescent Thoroughbreds are
caused by training and not by growth. The most noticeable
change was for the SDH activity of type-IIX/B
fibers. These changes in the gluteus medius muscle of
adolescent Thoroughbreds were considered to be
appropriate adaptations to running middle distances at
high speeds. (Am J Vet Res 2002;63:1408–1412)
Objective—To compare methods for harvesting canine bone marrow stromal cells (BMSCs) and determine the biological properties of canine BMSCs at successive passages in vitro.
Sample—BMSCs collected from the femurs of 9 Beagles.
Procedures—A fibroblast assay was performed to compare 2 methods for harvesting BMSCs: the aspiration and perfusion method. Flow cytometric analysis was performed to evaluate the cell surface markers. Changes in proliferative activity were analyzed by examining radioactivity of hydrogen 3-thymidine. Cell senescence was studied via senescence-associated β-galactosidase staining, and differentiation properties (osteogenesis and adipogenesis) were estimated in association with passage.
Results—The aspiration method yielded significantly more fibroblasts than the perfusion method. The cells harvested by both methods gave positive results for CD44 and CD90 and negative results for CD34 and CD45. After induction, the cells had osteogenic and adipogenic phenotypes. The biological properties of BMSCs harvested by the aspiration method were estimated in association with passage. With increasing number of passages, the proliferative activity was reduced and the proportion of cells with senescence-associated β-galactosidase staining was increased. The capacity of differentiation was reduced at passage 3.
Conclusions and Clinical Relevance—The aspiration method was superior for collection of BMSCs. In early passages, canine BMSCs had the proliferative activity and potential of osteogenic and adipogenic differentiation, but this decreased with increased number of passages. Consideration of passage will be important to the success of any strategy that seeks to regenerate tissue though the use of BMSCs.