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Received July 21, 2003
Revised September 4, 2003
Accepted after revision October 14, 2003
1 Royal Free and University College Medical School
2 Bispebjerg Hospital
3 Copenhagen Muscle Research Centre
* To whom correspondence should be addressed. E-mail: m.hameed{at}rfc.ucl.ac.uk.
The expression of two isoforms of insulin-like growth factor-I (IGF-I): mechano growth factor (MGF) and IGF- IEa were studied in muscle in response to growth hormone (GH) administration with and without resistance training in healthy elderly men. A third isoform, IGF-IEb was also investigated in response to resistance training only. The subjects (age 74 ± 1 year, mean ± SEM) were assigned to either resistance training with placebo, resistance training combined with GH administration or GH administration alone. Real time quantitative RT-PCR was used to determine mRNA levels in biopsies from the vastus lateralis muscle at baseline, after 5 and 12 weeks of training. GH administration did not change MGF mRNA at 5 weeks, but significantly increased IGF-IEa mRNA (237%). After 12 weeks, MGF mRNA was significantly increased (80%) compared to baseline. 5 weeks of resistance training significantly increased the mRNA expression of MGF (163%), IGF-IEa (68%) and IGF- IEb (75%). No further changes were observed after 12 weeks. However, after 5 weeks of training combined with GH treatment, MGF mRNA increased significantly (456%) and IGF-IEa mRNA by (167%). No further significant changes were noted at 12 weeks. The data suggest that when mechanical loading in the form of resistance training is combined with GH, MGF mRNA levels are enhanced. This may reflect an overall upregulation of transcription of the IGF-I gene prior to splicing.
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