Skeletal and cardiac muscle protein turnover during short-term cold exposure and rewarming in young rats

Abstract

Young animals exposed to cold environmental temperatures typically have decreased skeletal muscle accretion but increased heart masses. To explore these phenomena, we measured protein synthesis and degradation in vivo in cardiac and skeletal muscle in weanling rats during short-term cold exposure and rewarming. Control rats were housed at 25 degrees C throughout the experiment. Ad libitum-fed and pair-fed (to the intake of controls) rats were housed at 5 degrees C (cold) for 5 days and then at 25 degrees C (rewarmed) for another 5 days. Cold exposure decreased rates of protein accretion and synthesis in skeletal muscle, whereas degradation did not differ. The effects of cold exposure on skeletal muscle were similar in both pair-fed and ad libitum-fed rats, except growth was lower in pair-fed rats. In cardiac muscle, cold exposure increased rates of protein synthesis and degradation and resulted in increased cardiac mass. Results in pair-fed animals generally fell between those of control and ad libitum-fed cold rats. During rewarming, growth rates were not higher in skeletal muscle in ad libitum-fed re-warmed rats, although protein turnover returned toward control values; in pair-fed rats, it remained lower. In heart, growth rates of ad libitum-fed and pair-fed rewarmed rats decreased due to lower protein synthesis rates. These alterations appear to be consistent with a strategy designed to improve survival in cold environments.

High-sugar diets increase cardiac dysfunction and mortality in hypertension compared to low-carbohydrate or high-starch diets

“…To our knowledge, this is the first study to assess protein synthesis in the heart with 2 H 2 O method. The values that we obtained (~1.0%/h) are similar to the values previously reported in conscious rats using the [2,6- 3 H]phenylalanine incorporation method [39]. From the increase in LV mass and the fractional synthesis rate, the relative imbalance between protein synthesis and breakdown that is required to result in LVH can be estimated.…”

Effects of 20-Week Intermittent Cold-Water-Immersion on Phenotype and Myonuclei in Single Fibers of Rat Hindlimb Muscles

“…However, the muscle weight normalized by body weight was even increased generally following cold exposure, suggesting that the cold-exposure-related inhibition of the gain was greater in whole body weight than that in each skeletal muscle. The responses of body and muscle weights to cold exposure are comparable to those reported elsewhere [3,15,16]. Chronic cold exposure causes a drop of body temperature [3,15,17].…”

“…The responses of fiber size observed in the present study are comparable with those reported by others [4,19]. Samuels et al [16] found that 10 days of cold exposure decreased the growth rate because of a lower rate of protein synthesis, instead of an increased rate of protein degradation. However, the mean sizes of all muscle fibers with different phenotypes in sea divers who have been diving 4-5 h daily during their life in water with temperatures ranging from 10-12°C to 25-27°C during the winter and summer, respectively, were smaller than those in non-divers [4].…”

Cold-impaired cardiac performance in rats is only partially overcome by cold acclimation

“…Prolonged exposure of rats to low environmental temperatures typically results in reduced skeletal muscle growth but increased heart mass, due to differential rates of in vivo protein synthesis and degradation (McAllister et al, 2000;Samuels et al, 1996). In guinea pigs, myocardial hypertrophy following CA-induced volume overload is compensated by increases in capillarity (Kayar and Banchero, 1985).…”