Interstitial IGF-I in exercising skeletal muscle in women.
OBJECTIVE
To study interstitial IGF-I concentrations in resting and exercising skeletal muscle in relation to the circulating components of the IGF-IGF binding protein (IGFBP) system.


METHODS
Seven women performed endurance exercise with 1 leg (Ex-leg) for 1 h. The resting leg (Rest-leg) served as a control. IGF-I was determined in microdialysate (MD) and was compared with veno-arterial (v-a) concentrations of circulating IGF-IGFBP components.


RESULTS
Median (range) basal MD-IGF-I was 0.87 (0.4-1.5) microg/l or 0.4 (0.2)% of total-IGF-I (t-IGF-I) determined in arterial serum and in the same concentration range as free dissociable IGF-I (f-IGF-I). Rest-leg MD-IGF-I decreased, reaching significance after exercise. Ex-leg MD-IGF-I was unchanged during exercise and declined after exercise at the level of significance (P = 0.05). There was a release of f-IGF-I from the Ex-leg into the circulation at the end of and shortly after exercise. A small but significant increase in circulating IGFBP-1 was detected at the end of exercise and IGFBP-1 increased further after exercise. Although interleukin-6 (IL-6) has been associated with IGFBP-3 proteolysis, the circulating molecular forms of IGFBP-3 remained unchanged in spite of an IL-6 release from the muscle compartment.


CONCLUSIONS
Circulating IGFBP-1 is related to interstitial IGF-I in resting muscle although the temporal relationship may not be simple. Further studies should explore the role of local release of IGF-I and its impact on IGF-I activity during contraction.
Berg
U
U
Pediatric Endocrinology Unit, Department of Woman and Child Health, Karolinska Institute, Astrid Lindgren Children's Hospital, SE-171 76 Stockholm, Sweden. ulrika.berg@ki.se
Gustafsson
T
T
Sundberg
C J
CJ
Kaijser
L
L
Carlsson-Skwirut
C
C
Bang
P
P
D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D015444:Exercise / Q000502:physiology*; D045604:Extracellular Fluid / Q000737:chemistry*; D005260:Female; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000097:blood; D018972:Insulin-Like Growth Factor Binding Protein 3; D018969:Insulin-Like Growth Factor Binding Proteins / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D015850:Interleukin-6 / Q000097:blood; D007866:Leg / Q000098:blood supply; D017551:Microdialysis; D018482:Muscle, Skeletal / Q000098:blood supply / Q000737:chemistry*; D012039:Regional Blood Flow
D001786:Blood Glucose; C032231:IGFBP1 protein, human; C515497:IGFBP3 protein, human; D018970:Insulin-Like Growth Factor Binding Protein 1; D018972:Insulin-Like Growth Factor Binding Protein 3; D018969:Insulin-Like Growth Factor Binding Proteins; D015850:Interleukin-6; D007334:Insulin-Like Growth Factor I