Context Little is known about the expression of skeletal muscle-specific isoforms of the insulin-like growth factor-I (IGF-I) gene in response to exercise in humans. Data for women are sparse and the influences of age and physical training status are unknown. Here we aimed to describe the expression of mRNA for the IGF-I isoforms in the quadriceps muscles of women at rest and after isometric exercise. Objective To categorise mRNA expression of the IGF-I splice variants IGF-IEa and IGF-IEc (MGF) in healthy women, determine whether isometric exercise stimulates expression, and to determine the duration of the response. Design Observational study. Setting Clinical research facility. Participants Six healthy women (median age 38 years, range 25–43 years). Intervention Single bout of maximal isometric knee extension undertaken as 20 sets of 6 contractions. Muscle samples from the lateral mass of the quadriceps were obtained by needle biopsy at baseline, 2.5 h and 50 h after exercise. Main outcome measures Quantification of mRNAs for IGF-IEa and MGF. Results mRNA for the IGF-IEa transcript was significantly elevated by 50 h post-exercise compared to baseline (p = 0.005) and mRNA for MGF was significantly elevated by 2.5 h (p = 0.026). There were no statistically significant differences between measurements at 2.5 h and 50 h for either transcript. Conclusions We have shown that the upregulation of the muscle specific IGF-IEa and MGF isoforms occurs within 2.5 h of a single bout of isometric exercise in women. The upregulation persists for at least 2 days after exercise. We have also demonstrated a potentially safe and effective way of studying the responsiveness of these isoforms to resistance exercise in future studies of older and/or frail individuals. |