Skeletal and heart muscle protein turnover during long-term exposure to high environmental temperatures in young rats

Abstract

A study was undertaken to determine the long-term effects of a hot environment on protein turnover in skeletal and cardiac muscles of young homeothermic animals. Three groups of 36 male 28 day old rats were housed at 35 degrees C (hot group), 25 degrees C (control group), or 25 degrees C but pair-fed to the intake of the hot group (pair-fed group). Rates of protein synthesis and degradation were measured in vivo on days 5, 10, 15, and 20. By day 20, soleus and gastrocnemius (skeletal muscle) protein masses were 7 and 14% lower in the hot group and 31 and 21% lower in the pair-fed group compared with the control group (P < 0.05). The fractional rate of protein synthesis (k(syn)) was on average 11% lower (P < 0.05) in the hot group compared with control rats and was not different from pair-fed rats. The fractional rate of skeletal muscle protein degradation (k(deg)) in hot rats was slightly lower than in control rats; k(deg) was on average 18% higher (P < 0.05) in the pair-fed group compared with the hot group and this difference appeared to be most prominent on day 5. In heart, by day 20, protein mass was 30% lower in the hot group and 40% lower in the pair-fed group compared with control rats (P < 0.05). k(syn) was on average 19% lower (P < 0.05) in the hot group compared with the control group, but not different from pair-fed rats. In the heart there were no differences in k(deg) among treatments. Plasma triiodothyronine (T3) concentration was lower in the hot group, but not in the pair-fed group, compared with controls. In conclusion, chronic exposure to hot environments was associated with lower skeletal and cardiac muscle mass and protein turnover; lower protein mass in this tissue was due to decreased k(syn); this is consistent with lower plasma T3 concentrations. In pair-fed rats, k(syn) was also reduced, but interestingly k(deg) was not, resulting in a greater loss of skeletal muscle mass. These results suggest that heat exposure invokes physiological adaptations to preserve skeletal muscle mass despite decreased food intake. In the heart, loss of protein was a result of decreased k(syn), which can be primarily ascribed to lower food intake.

Fetal and neonatal programming of postnatal growth and feed efficiency in swine

“…Thus, growing-finishing, gestating or lactating swine are highly susceptible to heat stress, as well as the associated oxidative stress, resulting in an excessive production of reactive oxygen species [26, 27]. Under experimental conditions, increasing environmental temperatures from 23 °C to 33 °C markedly reduces feed intake, growth performance, and the efficiency of nutrient utilization for weight gains in swine [28–30], and, at the same time, impairs immune responses [31] and muscle protein synthesis [32]. Interestingly, the pig’s breed does not influence physiological responses to thermal stress [33, 34].…”

Heat Acclimation, Epigenetics, and Cytoprotection Memory

“…Whereas the major adaptive targets in the heart are genes associated with excitation contraction coupling and Ca 2+ signaling, in the soleus, upregulation of metabolic genes is noted. Samuels et al 2000 (184) demonstrated that chronic heat exposure invoked physiological adaptations that preserved skeletal muscle mass (in contrast to the Figure 13 Expression level of (i) Ecitation-contraction coupling and Ca 2 regulatory genes in the heart and (ii) energy metabolism associated genes in the soleus. No other differences in functional categories expression levels were detected between the groups.…”

Protein and Amino Acid Metabolism in Poultry during and after Heat Stress: A Review

“…The effects of HS on protein turnover are controversial but may be related to the magnitude and duration of the heat load producing either a detrimental or therapeutic effect. Both HS and pair feeding reduced the muscle mass of rats; however, pair-fed animals had higher protein degradation, leading to a more severe loss of skeletal muscle that might be attributed to protein preservation triggered by heat exposure [41].…”