The aim of this study was to increase growth hormone (GH1) and insulin-like growth factor-1 (IGF1) levels in rat muscle indirectly through the transduction of C2C12 cells via lentivectors and to compare their effects on muscle mass. The coding sequences of GH1, IGF1, and GH1-IGF1, linked by the 2 A self-cleaving peptide to enable polycistronic expression, were synthesized, cloned and inserted into the pCDH vector. Recombinant pseudolentiviruses containing our target genes were produced in HEK293T cells. C2C12 cells were transduced with pseudo lentiviruses and selected through resistance to puromycin antibiotics. The expression of the GH1 and IGF1 genes at the mRNA and protein levels was verified by RT–PCR and Western blotting, respectively. The recombinant pseudo lentiviruses and transduced C2C12 cells were injected into the tibialis anterior (TA), gastrocnemius and quadriceps muscle groups of eight-week-old rats. The body weights of the rats were measured weekly for eight weeks after the injection. The leg weight and histology of the muscle after eight weeks were also measured. The results revealed the expression of the GH1 and IGF1 genes at the mRNA and protein levels in C2C12 cells. An increase in both hormones, either directly or indirectly through C2C12 cells, increased the animal body weight, leg weight, and muscle fibre size after eight weeks. The direct and indirect transfer of IGF1 increased body weight, leg weight and muscle fibre size more than did the direct or indirect transfer of GH1. In the direct transfer groups, the body weight was greater than that in the indirect transfer groups after eight weeks. We demonstrated that nonpituitary secretion of GH1 mimicked some physiological effects of pituitary GH1 in a rat model. Further investigations are needed to study other possible effects of extra copy of GH1 and IGF1 genes over a longer period on other tissues.

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