83

Effect of work-load exercise on the compensatory muscle
hypertrophy in the albumin-deficient rat
Shigeru Yamada
Department of Sports Sciences, College of Arts and Sciences, the University of Tokyo,
3-8-t Komaba, Meguroku, TokYo 153
Summary

To study the role of albumin in the work'induced hypertrophy in skeletal muscle, effect of workload exercise on skeletal muscles of the albumin-deficient rat (Nagase Analbuminemia Rat; NAR) wascompared with those of normal rats. The work-induced muscle hyPertrophy, which is constantly
observed with normal rats, failed to take place in NAR.

Key liords: Albumin, Skeletal muscle, Compensatory hypertrophy, Albumin-deficient rat

Introduction
Much interest has been focused in recent years on the mechanisms leading to compensatory
hypertrophy in skeletal muscle (1, 2,3, 4, 5).In the previous paPer (5), we reported that the tenotomyinduced hypertrophy in the rat skeletal muscle accompanies a significant increase in the level of a
specific protein with a molecular weiSht of approximately 64,000 Daltons. This protein, designated"64KDa protein", has been identified as rat albumin based on biochemical and irnnunological criteria(5). Moreover, the result of isotope incorporation experiments suggested that albumin in lat skeletal
muscle is most likely to be synthesized in muscle cells and the rate of its synthesis is significantly
elevated in the hypertrophied muscle (5). These observations imply a possible correlation between
albumin and the compensatory muscle hypertrophy. Thus, the Present experiments have been designed
to elucidate the role of albumin in the work-induced enlargement of skeletal muscle. For the purposeof these experiments, we took advantage of using a mutant rat strain which has a defect in albumin
synthesis. The albumin deficient rat, termed "Nagase analbuminemia Rat" (abbreviated as NAR), is amutant of the Sprague Dawley rat which lacks albumin in serum (6). The molecular processes whichbring about the absence of serum albumin in this mutant rat have been recently established. The NAR
has a defect in the nuclear splicing of the primary transcipt from the albumin gene, producing a
non-functional albumin mRNA (7). If albumin in skeletal muscle is coded for by the gene which also
cordes for serum albumin and if atbumin participates in muscle enlargement, then the processes leading
to the compensatory muscle hypertrophy strould be impaired in NAR. In the present study, changes inmuscle weight and protein components in the work-loaded skeletal muscles of NAR were comparedwith those of normal mts.

Materia.ls and Methods

Animals
Nagase analbuminemia rats (NAR) derived from JCLSprague Dawley rats were kindly suppliedby Dr. sumi Nagase, sasaki institute, Tokyo. Normal sprague-Dawley rats were obtained from thestock of CLEA Japan, Kanagawa.

Tenotomy

Rats of the sarne developmental stage were divided into control and experimental groups byweight'matching. Tenotomy and sharn-opcmtion of the hind legs were performed in the sarne manneras described previously (5). The plantaris and the soleus muscles in both operated and contralaterallimbs were removed for examination 7 days after operation.
Polyacrylamide gel electrophoresis
Polyacrylamide gel electrophoresis was performed as described by Laemmli (8) on lwo acrylamide slab gels. Total muscle proteins were dissolved in a sample buffer, containing 25 mM Tris-HCl, 2%SDS, pH 6.5 and heated in boiling water for 2 min. Electrophoresis was performed at 25 mA constantcurrent until the bromophenol blue tracking dye moved to the end of the gel. After electrophoresis,

proteins were stained with Coomassie blue (5).

Results

Effect of tenotomy and exercise on muscle hyperhophy in the analbumineia rat
To study the effect of work-load exercise on the muscle hypertrophy in NAR, the soleus and theplantaris muscles of one limb were workioaded by tenotomy of the synergistic gastrocnemius muscle.
The contralateral limb which received only sham-operation served as control. During one week following tenotomy, the work-loaded muscles of the tenotomized limb of NAR failed to exhibit statisticallysignificant changes in wet weight as compared to those of control muscles (Table l). By contrast, weroutinely observed 30-507a weight gain in the work-loaded muscles of normal rats when the synergisticmuscle was tenotomized (5).

Effect of tenotomy on muscle protein components
To ascertain whether the work-load exercise brings about qualitative or quantitative change in theprotein components of the skeletal muscles of NAR, total protein from the work-loaded and control
muscle were analyzed by means of sDS polyacrylamide ger electrophoresis. Densitometric tracings ofthe staining patterns clearly demonstrate that the amount of albumin in the muscle preparations ofNAR, either work-load or control, is negligible, while marked increase in albumin content is noticed in
the work-loaded muscle of normal rat (Fig. l). These results not only reaffirms that 64 KDa protein israt albumin, but also strongly suggest a correlation between albumin and exercise-induced muscle

hypertrophy.

Teble l. Effect of tenotomy and exercise on weight of skeletal muscles ofnormal and analbuminemia rats

Rat Strain

NAR(n‐ 5)

Normalrll=5)

MusclcControlWork loaded

Plantaris

950± 1311094■ 197

Soleus596±45844■ 269

Plantaris1035±

フ41408■

Soleus603± 108

89*837■ 103拿

Values are means r SD for 5 muscles. + P<0.01

ＦＥＥＥＩＥＥ

B

ＥＥＬ
監
勝鬱

彎CH‑Fig. l. SDs-polyacrylamide gel electrophotesis ol muscle proteins. The plantaris muscles from thetenotomized (H) and shamrperated (C) timbs of NAR were removed ? days aftel operationand each muscle was solubilized with 4 ml of SDS sample buffel (3). Each 15 ! I of solution(20 p g protein) was subjected to SD$polyacrylamide gel electrophoresis and stained forprotein with Coomassie b1u€ (A). Electrophoreograms of muscle proteins were traced by adensitometer (B). Arrows indicate the position of muscle albumin. Direction of electrophoresis
was from left to right.

86Discusion

In the previous paper, compensatory hypertrophy in the rat skeletalmuscle accompanies an increasein muscle concentration of albumin (5). Studies on th€ physiological role of albumin in compensatory
muscle hypertrophy would be geatly facilitated by the availability of a rat strain defectiye in albuminbiosynthesis (6,7). In the present experiments, tenotomy was performed on the skeletal muscle ofalbumin deficient rats (NAR) and changes in weight and protein composition of the work-loaded
synergistic muscles were compared with those of normal rats. In contrast to the case with normal rats,
we found that NAR fails to develop significant muscle hypertrophy in response to the workload
training. The result strongly suggests the positive inyolyement of albumin in the work-induced enlarge,
ment of skeletal muscle, though mechanisms by which albumin participates in the muscle hypertrophy
remain to be elucidated.

Refetences

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2) Hofmann, W.W.: (1980) J. Neuro. Sci.45, 205-216.
3) Gutmam, E., Schiaffino, S.and Hanzlikova, V.: (1971)Exp. Neurol.3t,451 464.
4) Schiaffino, S. and Hanzlikova, V.: (1970) Expedential 26 (2), 152-153.
5) Yamada, S., Tomino, S., Izumi, S. and Akino, M.: 0984) B.B.A. ?98,260-267.
6) Naga3e, S., Shimamune, K. and Shumiya, S.: (1980) Jikken Dobutsu 29, 33 38.
7) Esumi, H., Okui, M., Sato, S., Sugimura, T. and Nagase, S.: (1980) proc. Natl. Acad,. Sci. jj,3215-3219.
8) Irammli, U.K.: (1970) Nature 227, 680.