Effects of Heat Stress on Prevention of Disuse Muscle Atrophy in Rat Soleus Muscle(Articles Supported by Grants from JPTA)

本研究の目的は,温熱負荷ならびに温熱負荷と持続的筋伸張運動を併用した場合の廃用性筋萎縮の進行抑制効果を明らかにすることである。実験動物は,7週齢のWistar系雄ラットで,1週間の後肢懸垂によってヒラメ筋に廃用性筋萎縮を惹起させるとともに,その過程で約42この温熱ならびに持続的筋伸張運動,両者を併用した方法を負荷し,筋湿重量とタイプI・II線維の筋線維直径の変化,Heat shock protein 70(Hsp70)の発現状況を検索した。温熱負荷によってHsp70の発現が増加し,タイプI・II線維とも廃用性筋萎縮の進行抑制効果を認めた。そして,これはHsp70の作用によってタンパク質の合成低下と分解完遂が抑制されたことが影響していると考えられた。一方,持続的筋伸張運動でも廃肝吐筋萎縮の進行抑制効果を認めたが,温熱負荷と併用した方法がより効果的であり,これはHsp70の作用と機械的伸張刺激の作用の相乗効果によるものと推察された。It is known that heat stress induces expression of heat shock protein 70 (Hsp 70) in myocytes. Hsp 70 plays an important role in chaperoning nascent peptides during translation, and it has been assumed that the elevation of cellular Hsp 70 levels can serve as a countermeasure to attenuate the disuse-induced reduction in protein synthesis. We therefore investigated the effects of heat stress, prolonged stretching, and heat stress combined with prolonged stretching on prevention of disuse muscle atrophy in rat soleus (SOL) muscle. Thirty Wistar rats were divided randomly into the control (Con, n=5), heat stress (Heat, n=5), hindlimb suspension (HS, n=5), HS and heat stress (HS&Heat, n=6), HS and prolonged stretching (HS&Stretch, n=5), and HS and heat stress combined with prolonged stretching (HS&Heat&Stretch, n=4) groups. Disuse muscle atrophy was induced by hindlimb unweighting for 7 days. Each rat in the Heat, HS&Heat, and HS&Heat&Stretch groups was anesthetized, and bilateral hindlimbs were immersed daily in hot water (42 ℃) for 60 min during HS. In HS&Stretch and HS&Heat&Stretch groups, both soleus muscles underwent prolonged stretching daily for 30 min during HS. At the end of the experimental period, the SOL muscles were extracted and weighed. Frozen sections were stained with myofibrillar adenosin triphosphatase (pH 10.5), and muscle fiber diameters of each fiber type were measured. To determine the levels of Hsp 70 in muscular tissue, we performed an enzyme-linked immunosorbent assay (ELISA) and western blotting methods. The weight of the SOL muscles relative to body weight for the HS&Heat, HS&Stretch, and HS&Heat&Stretch groups increased significantly compared with the HS group. The mean muscle fiber diameter of type I and II for the HS&Heat, HS&Stretch, and HS&Heat&Stretch groups increased significantly compared with the HS group. HSP 70 levels were significantly greater in the Heat, HS&Heat, and HS&Heat&Stretch groups compared with the Con, HS, and HS&Stretch groups. Our results suggest that the progression of disuse muscle atrophy can be attenuated by heat or stretch, and this mechanism is related to the expression of Hsp 70 or mechanical stretch in myocytes