Objective—To investigate influence of the
Rendement Napole (RN–) mutation on proglycogen
(PG) and macroglycogen (MG) content in skeletal
muscles before and after exercise and evaluate glycogen
concentrations within various muscle fiber types.
Animals—5 pigs with the RN– mutation and 3 noncarrier
Procedure—Pigs performed 2 exercise tests on a
treadmill. In the first, pigs (mean body weight, 27 kg)
ran a distance of approximately 800 m. In the second,
pigs (mean body weight, 63 kg) ran until fatigued.
Biopsy specimens (biceps femoris muscle) for determination
of PG and MG contents were obtained
before and after exercise, 24 hours after the first test,
and 3 hours after the second test. Histochemical
analysis was performed on specimens obtained
before and after the second test.
Results—Before exercise, PG stores did not differ
markedly between groups, but MG stores were
twice as high in pigs with the RN– mutation, compared
with noncarrier pigs. The MG content
decreased to a similar extent in both groups after
exercise. Resynthesis of MG was greater in pigs with
the RN– mutation than in noncarrier pigs by 3 hours
after exercise. A low glycogen content after exercise
was observed in many type I and type IIA fibers and
in some type IIB fibers.
Conclusions and Clinical Relevance—The RN– mutation
was associated with high MG stores in skeletal
muscle that did not influence exercise performance.
The RN– mutation did not impair glycogenolysis during
exercise but may induce faster resynthesis of MG
after exercise. (Am J Vet Res 2005;66:1197–1201)