Chronic intermittent cold exposure did not affect β-hydroxyacyl-CoA dehydro genase activitiy in rat soleus muscle
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(2) Chronic intermittent cold exposure did not affect B-hydroxyacyl-CoA dehydro genase activitiy in rat soleus muscle Junichi SUZUKI Research and Education Center for Winter Sports, Hokkaido University of Educalion, 5-3 Ainosato, Kim- ku, Sapporo, Ho kkfdo 002-3502,Japan Abstract The effects o f 4-week intermittent cold exposure on enzyme activities concerning citric acid cycle and B-oxidation were studied in soleus muscles in female Wistar rats. The rats were randomly divided into control (CNT, n=5) and cold-acclimated (CA, n=6) groups. All rats were housed under condition of control temperature (24+F "C). The rats of CA group were subjected to cold chamber set at 5*1 O C . The duration of cold exposure was 2 hours per day, and lasted for 4 weeks from the age of 12 weeks. Body weight at the time of sacrifice did not significantly different between the two groups. The weight of interscapular brown adipose tissue significantly increased by 71% after the cold exposure (Pc0.05). The activity of 0hydraxyacyl-CoA dehydrogenase (HAD), the key enxyme of B-oxidation, did not change after the cold exposure. The activity of citrate synthase (CS) tended to increase by 12% after the cold exposure, but the difference was not significant. The HADtCS ratio showed, but not significantly, lower value in the CA than CNT. These results suggest that the present type o f cold exposure does not improve the capacity of fatty acid utilization in muscle mitochondria.. Key words: O-hydroxyacyl-CoA dehydrogenase; cold acclimation; citrate synlthase; skeletal muscle When the homeotherms are exposed to a cold atmosphere, thermogenesis in the skeletal muscles as well as in other organs is enhanced [1,2,6,7]. In hind-limb muscles, an increase in the oxidative enzyme activity was observed after chronic cold exposure [4,9,10]. In our previous study, succinate dehydrogenase activity was increased in soleus and deep portion of gastrocnemius muscles, but not in superficial portion of gastrocnemius muscle after cold acclimation (5 "C for 4 weeks) [lo]. It is therefore possible that an increase in oxidative enzyme activity is observed after cold acclimation in the skeletal muscles that are mainly composed of oxidative fibers. Adan el a1 (1995) determined the energy sources used to maintain muscle shivering during acute cold exposure (4 "C) for up to 2 h [I]. In their study, substrate sifted from glucose andlor glycogen to triacylglycerol (TG).Therefore it is postulated that the capacity of TG utilization, i.e,, 0-oxidation of mitochondria, is enhanced after repetitive intermittent exposure to cold atmosphere, even though duration. of daily exposure is short, around 2 hours. However, the capacity of B-oxidation in skeletal muscle after intermittent cold exposure has not yet been determined. The present study, therefore, observed the activity of l3-hydroxyacyl-CoA dehy drogenase (HAD) in rat soleus muscle after intermittent cold exposure for 4 weeks.. Methods. Animals Eleven female Wistar rats (I0 weekold) were purchased from Clea Japan Inc. (Tokyo, Japan). After the rats were fed for 14 days to allow adaptation to the new environment, the rats were randomty divided into two groups; warm control (CNT; n=5) and cold-acclimated group (CA; n=6). All rats were housed under conditions of control temperature (242~1 'C) and a relative humidity of about 50%. Lighting (7:OO- 19:OO) was controlled automatically. All rats were given commercial laboratory chow (CE-2, Clea Japan Inc.) and tap water.
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