93

Effect of work-load exercise on the compensatory muscle
hypertrophy in the hypophysectomized rat
Shigeru Yamada
Department of SPorts Sciences, CoUege of Arts and Sciences, the University of Tokyo,
3-8-l Komaba, Meguro-ku, TokYo 153

Summary

To study the role of growth hormone in the work-induced hypertrophy in skeletal muscle, effectsof work-load exercise on skeletal muscles of hypophysectomized rat was compared with those ofnormal rats. The work-induced muscte hypertrophy was observed with hypophysectomized rat. The
development of compensatory muscle hypertrophy and the accumulation of albumin in the workloaded muscle took place in the hypophysectomized rat.

Key Words: Atbumin, Skeletal muscle, Compensatory hypertrophy, Growth hormone.

Introduction
We have been studying the mechanisms bringing about the work-induced hyPetrophy in the rat
skeletal muscte and found that the tenotomy-induced hypertrophy in the skeletal muscle accompanies
a significant increase in concentration of albumin in the hypertroPhied muscle (l). The observationthat the mutant rat defective in albumin synthesis failed to develop the work-induced muscle
hypertrophy strongly suggested the possible correlation between the muscle albumin concentration andhypetrophy (2). However, the albumin deficient rat is also known to exhibit the lowered in born levelsof testost€rone ard growth hormone (3). To rule out the possibility that the loweled tostosterone level
might affect the development of the work-induced muscle hypertrophy, we studied the effect ofwork-load exercise on the skeletal muscle of the castrated male rats (4). This paper deals with theexperiments on tlle work-load exercise in the skeletal muscle of the hypophysectomized rat and showsthat neither growth hormone nor testosterone are primarily involved in the workinduced enlargement

ofthe rat skeltal muscle.

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Materials and Methods

Animals
Sprague-Dawley rats were obtained from the stock of CLEA Japan, Kanagawa.

Tenotomy

Rats of the same developmental stages were divided into control and experimental groups byweight-matching. Tenotomy and sham-operation of the hind legs were performed in the same manneras described previously (l). The plantaris and soleus muscles in both operated and contralateral limbs
were removed for examination 7 days after operation.

Hypophysectomy
Rats weighing 70 to 95 g were anesthetized as above and hypophysectomized. The hypophysecto,mized rats were maintained for 3 to 4 weeks before use, at which time they weighed 100 to 120 g.
Assay of growth hormone

Blood samples were centrifuged and growth hormone in plasma was determined by a doubleantibody radioimmunoassay method using materials zupplied by NIADDK (5).
Pr€paration of sntibody

Anli-64KDa protein antibody was prepared as described previously (l).
Polyacrylamide gel electrophoresis and immunoblotting
Methods for potyacrylamide gel electrophoresis and immunoblotting were performed in the samemanner as described previously (1, 4).

Results

The effect of growth hormone on compensatory muscle hypertrophy was studied. Figure I showsthat the gro}vth hormone concentration in the hypophysectomized rats was negligible as compared tothat in the sham-operated rats. To study the effect of work-load exercise on the muscte hypertrophy

in hypophysectomized mt, the soleus and the plantads muscles of one limb were work-loaded bytenotomy of the synergistic gastrocnemius muscle. The contralateral limb which received only shamoperation served as control. During the week following tenotomy, the workJoaded muscles of thetenotomized limb of hypophysectomized exhibited statistically significant increase in wet weight ascompared to those of control muscles (Fig. 2). Total protein from the work-toaded and the control
muscle were anzlyzed, by means of SDS polyacrylamide gel electrophoresis (Fig. 3A). Changes inmuscle albumin levels were compared between hypertrophied and control muscles of the hormone-depleted rats by means of western-blotting (Fig. 3B). As observed in the case of normal rats. theamount of albumin significantly increased in the work-loaded muscles of the hormone-depleted animals.
These results slrongly suggest that the possible correlation between albumin and exercise-induced
muscle hypertrophy and that growth hormone is not essential for the development of muscle
hypertrophy.

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Discussion

Among biochemical parameters which may influence th€ rate of muscle hypertrophy, serum levelgrowth hormone is known to exert pronounced effects (6,7,8,9,1O,11,12, 13, 14,). Pituitary groi thhormone is essential for normal growth of most body tissues in mammals. (17). Thus hypophysectomy
prevents normal growth of mammals, while administration of excess growth hormone leads to gigan-tism (8, I I , 13, 15, 16). Although the lesponse of different tissues to treatment with these hormones is
not uniform and the mechanisrns by which these hormones affect muscle mass and muscle protein
composition remain only poorly understood, the accumulated facts raise the possibility that theobserved inability of the NAR skeletal muscte to respond to work load training might be the consequ-ence of the lowered inbom levels of testosterone and gowth hormone in this mutant rat (3).
Therefore, the effect of hypophysectomy on compensatory muscle hype rophy was examined innormal rats as respects muscle enlargement and albumin accumulation. The results show that com'pensalory muscle hypertrophy is inducible in the hypoPhysectomized rats. Moreover, muscle
hypertrophy observed with this oryan-ectomized rats also accompanied albumin accumulation in

the hypertrophied muscle. Successful induction of the compensatory muscle hypertrophy in thehypophysectomized rats is well in agreemeflt with the Goldberg's statement that growth hormone
has no effect on tenotomy-induced muscle hypertrophy (17). Taken together, the present results,suggest that Browth hormone is not essential for the induction of muscle hypertrophy.

日 ぁじ ｏ目ｏ日ち 工︵■一■８ ０NHof hypophysectomy on the serum growth hormone concentlation Norma'l male latsFig.
- l. Effectwere hypophysectomized and level of serum growth hormone was determined by radioim'
munoassay as described in "Mateflals and Methods", N and H indicate the 8io*'th hormone
concentation in setum of normal and hypophys€ctomized rats, respectively Blood war drawn
from the abdominal aorta at 15-20 min after sodium pentobarbital injection'

６こ 一
島Ｆ′ｏｏ３¨- C HCH

Soleus I'lantaris

Fig.2. Effects of tenotomy and tiaining on the weight of the plantaris and soleus muscles in thehypophys€ctomized rats. Expeimental conditions aae desc bed in ..Materials and Methods',.
H and C indicate the muscle weight of the tenotomized and sham-operated limbs after training,rcspectively. The muscle weights are represented as a mean value.

AB

一一CHCHFig. 3. SDs-polyacrylamide gel electrophoresis and Westem blot analysis of the hypertrophied andcontrol muscles of the hypophysectomized rat. Conditions for hypophysectomy and tenotomy
were as descdbed in "Materials and Methods,'. After tenotomy and training for 7 days, tlre
plantaris muscle of the tenotomized (H) and control (c) limbs were dissected and sorub izedinSDS sample bufier. Each l2 pl of solution (25 ,Ig protein) was subjected to SDs-polyaoylamide

gel electrophoresis and stained for protein with Coomassie blue (A). proteins in the gel waselectiophoretically transfered to nitrocelulose firter. The filter was treated with anti-rat
albumin antibody and peroxidase-conjugated anti-rabbit IgG, and stained forperoxidase activity
as described in "Mateiais and Methods,, (B).

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