Effect of training and growth hormone suppression on insulin-like growth factor I mRNA in young rats

Abstract

The growth hormone (GH)-insulin-like growth factor I (IGF-I) axis plays a role in the adaptation to exercise training, but IGF-I gene expression in response to exercise training and GH suppression has not been studied. Twenty female rates underwent a 4-wk treadmill training program begun in the prepubertal period (day 14 of life). In 10 of the training rats, GH production was suppressed by anti-GH-releasing hormone antibodies (GH suppressed). IGF-I mRNA and protein levels were measured in liver and hindlimb skeletal muscle. GH suppression reduced IGF-I mRNA expression in the liver to a much greater extent than in the muscle. In the GH control rats, training induced significant increases in hepatic exon 1-derived IGF-I mRNA (mean increase 30%; P < 0.05) and muscle exon 2-derived mRNA (mean increase 35%; P < 0.05). In the GH-suppressed rats, only muscle exon 1-derived transcripts were significantly increased by training (55%; P < 0.05) and this was associated with a significant increase in muscle IGF-I protein levels (P < 0.05). We speculate that the anabolic response to training may involve both GH-dependent increases in IGF-I mRNA in the liver and GH-independent increases in the muscle.

IGF-I system responses during 12 weeks of resistance training in end-stage renal disease patients

“…These findings raise important questions concerning the relative contributions of the systemic vs. local IGF-I system toward training adaptations. For example, Zanconato et al [24] reported increases in local IGF-I gene expression and production despite no changes in circulating IGF-I after exercise training on rats. Recent work has demonstrated the existence of two different IGF-I isoforms in human skeletal muscle (one isoform identical to the liver derived form and one isoform responsive to mechanical stretch, termed mechano growth factor [MGF]) [25].…”

Growth hormone and mild exercise in combination increases markedly muscle mass and tetanic tension in old rats

“…Therefore, IGF-I seems to be involved in muscle regeneration and growth, and IGF-I produced locally in¯uences muscle cell growth via autocrine and paracrine mechanisms in concert with systemic IGF-I. The studies of Zanconato et al (42) suggest that exercise results in both GHdependent increases in IGF-I mRNA in the liver and GHindependent increases locally in the muscles. In old mice, exercise increased the IGF-I receptor-binding capacity and af®nity and stimulated protein synthesis (43), and adenoviral delivery of the IGF-I gene to skeletal muscles has been shown to increase muscle mass in old mice (44).…”

Effects of swimming training on bone mass and the GH/IGF-1 axis in diabetic rats

“…This process is responsible for most of the IGF-1 found in the circulation [9]. Exercise training can stimulate local muscle production of IGF-1, even in the absence of GH [10]. Regular exercise improves metabolic control in diabetic individuals and is an important component of treatment in diabetes mellitus [4].…”