RÉSUMÉ
Objective To establish an overload-induced hypertrophy model in aged rats by severing the distal tendon of gastrocnemius muscle, and to investigate the effect of vitamin D on overload-induced hypertrophy and the related mechanism. Methods A total of 20 male rats (24 months old) underwent tenotomy of the achilles tendon of the gastrocnemius muscle in the left hind limb; and a control sham operation was performed on the right hind limb. The rats were randomly divided into control group and experimental group. Experimental group received 1 000 IU/kg of vitamin D by intragastric administration, and the control group was given soybean oil. The animals were sacrificed one week later, the blood samples were collected, and the left, right hind musculus plantaris tissues were weighed and kept in liquid nitrogen. ELISA assay was used to examine serum 25(OH)D level and vitamin D receptor (VDR) in the skeletal muscle. Western blotting analysis was used to examine mTOR, rpS6 protein and their phosphorylation. Results The food intake and body mass were not significantly different between the two groups. Compared with the control side, vitamin D supplement significantly increased the muscle mass of the overload side in both groups (P<0. 05); and the mass of the overload side in the vitamin D supplement group was significantly higher than that in the control group (P<0. 05), while the mases were not significantly different for the sham sides in the two groups. The results of ELISA assay showed that vitamin D supplement significantly increased serum 25(OH)D levels in rats compared with the control group (P< 0. 05), and significantly promoted the expression of VDR in the overload side compared with the Sham side (P<0. 05), while there was no significant difference between the two sides in the control group. Western blotting analysis showed that p-rpS6/rpS6 and p-mTOR/mTOR ratios in the overload sides were higher than those in the Sham sides, but significant difference was only found for the vitamin D supplement group (P<0. 05). Conclusion Tenotomy of the achilles tendon of the gastrocnemius muscle can effectively promote the skeletal muscle hypertrophy in aging rats, and vitamin D supplement can further enhance overload-induced skeletal muscle hypertrophy, which might be related to VDR expression in skeletal muscle and protein synthesis protein mTOR and rpS6.