Serum IGF-I levels and IGF-I gene splicing in muscle of healthy young males receiving rhGH

Objective: Elevated growth hormone (GH) levels lead to increased circulating insulin-like growth factor-I (IGF-I), but the effects oil localised muscle IGF-I splice variant expression is not known. The effects of rhGH administration. with or without an acute bout Of high resistance exercise, were measured oil serum IGF-I and oil the mRNA levels of IGF-I splice variants in the vastus lateralis muscle of healthy young men. Design: The Study was a randomised double blind trial with a crossover design. Seven subjects were randomly assigned to a group receiving daily injections of rhGH (0.075 IU kg(-1) day(-1)) or placebo for a two week period. Following a one month washout. the groups were reversed. Results: Administration of rhGH increased circulating IGF-I from 31.8 +/- 3.2 to 109 +/- 5.4 nmol/L (p < 0.05). There was no effect of the exercise bout. RNA was extracted from muscle biopsies obtained from exercised and non-exercised legs 2.5 h after the cessation of the exercise. Transcript expression was measured using Real-time QPCR. There was no effect of either exercise or rhGH administration oil IGF-I 5' (Class 1 or Class 2) or 3' (IGF-IEa, or MGF) transcripts. Conclusion: Although rhGH administration has all effect oil liver IGF-I expression, as shown by increase ill circulating IGF-I. muscle IGF-I expression is unaffected ill Young healthy Subjects with normal GH profile. The findings contrast with those of a Previous Study in which GH deficient elderly men showed higher Muscle IGF-I 3' splice variant levels following rhGH administration with and without resistance training. Unlike in the liver, muscle Class 1 and 2 IGF-1 expression do not change significantly following administration of rhGH. (C) 2008 Elsevier Ltd. All rights reserved.