Post-exercise hot-water immersion is not effective for ribosome biogenesis in rat skeletal muscle.

Ribosome biogenesis is an important regulator of skeletal muscle hypertrophy induced by repeated bouts of resistance exercise (RE). Hot-water immersion (HWI), a widely used post-exercise recovery strategy, activates the mechanistic target of rapamycin (mTOR) signaling, a key regulator of ribosome biogenesis in skeletal muscle. However, the effect of HWI on skeletal muscle ribosome biogenesis is not well understood. Here, we aimed to investigate the effects of HWI and post-exercise HWI on ribosome biogenesis using a rat RE model. Male Sprague-Dawley rats were randomly assigned to HWI and non-HWI groups. In both groups, the right leg was isometrically exercised using transcutaneous electrical stimulation, while the left leg was used as an internal non-RE control. Following RE, both limbs were immersed in hot water (41.2 ± 0.03℃) for 20 min under isoflurane anesthesia in the HWI group and the gastrocnemius muscles were sampled at 3 and 24 h post-exercise. HWI significantly increased mTOR signaling and c-Myc mRNA expression, whereas post-exercise HWI significantly increased transcription initiation factor-IA mRNA expression. However, neither HWI nor post-exercise HWI enhanced 45S pre-rRNA expression, ribosomal RNA, or ribosomal protein content. Additionally, HWI tended to decrease 28S rRNA and 18S rRNA content, widely used markers of ribosome content. These results suggest that HWI as a post-exercise recovery is not effective in activating ribosome biogenesis.