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J Clin Endocrinol Metab. 2010 Sep;95(9):E64-8. doi: 10.1210/jc.2010-0689. Epub 2010 Jun 9.

Exercise and fasting activate growth hormone-dependent myocellular signal transducer and activator of transcription-5b phosphorylation and insulin-like growth factor-I messenger ribonucleic acid expression in humans.

Author information

1
Department of Medicine and Endocrinology, Aarhus University Hospital, 8000 Aarhus C, Denmark. mikkel.vendelbo@ki.au.dk

Abstract

CONTEXT:

GH secretion is increased by stress, such as fasting and exercise.

OBJECTIVE:

Our study was designed to test the hypothesis that fasting and exercise increase GH levels, GH-dependent signal transducer and activator of transcription (STAT)-5b phosphorylation, and IGF-I mRNA levels in human skeletal muscle.

DESIGN AND PARTICIPANTS:

Eight healthy men (25.5 +/- 4.3 yr) were studied for 6 h (a 4 h basal and a 2 h clamp period) in the basal state and after 72 h fasting and a 1-h ergometer cycling at 65% maximal oxygen uptake. Muscle biopsies were taken at t = 30 and 270 min.

SETTING:

The study was conducted at a university clinical research unit.

RESULTS:

During exercise, GH concentrations rapidly increased to greater than 10 ng/ml (P < 0.001). Thirty minutes after exercise, we observed a 4-fold increase in signal transducer and activator of transcription (STAT)-5 phosphorylation (P < 0.001) followed by an increase in IGF-I mRNA after 270 min (P = 0.026). During fasting, more sporadic GH bursts occurred, leading to an overall 3-fold increase in GH area under the curve(t=0-270) (P < 0.001). Similarly, STAT5 patterns were less consistent, with a tendency toward increased phosphorylation (P = 0.067, area under the curve(t=0-270)), whereas IGF-I mRNAs were persistently increased (P < 0.01).

CONCLUSIONS:

Our data show that myocellular GH signaling is stimulated after exercise and fasting in terms of increased STAT5 phosphorylation and/or IGF-I gene expression. This suggests that exercise with brief, well-defined GH peaks leads to distinct STAT5 phosphorylation and subsequent IGF-I gene expression, whereas fasting induces more sporadic GH bursts and less distinct but more persistent activation of the GH signal.

PMID:
20534752
DOI:
10.1210/jc.2010-0689
[Indexed for MEDLINE]

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