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  • Author: Søren Peter Jørgensen x
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Anne Vestergård Møller, Søren Peter Jørgensen, Jian-Wen Chen, Anni Larnkjær, Thomas Ledet, Allan Flyvbjerg and Jan Frystyk

Background: It is unclear how IGFs become separated from their IGF-binding proteins (IGFBPs) in vivo. However, the IGFBPs possess binding sites for glycosaminoglycans (GAGs) and interaction with GAGs alters IGFBP ligand affinity. Accordingly, GAGs may control IGF bioavailability. To test this hypothesis, we investigated the effect of GAGs on serum levels of free and bioactive IGF-I, total IGF-I, and IGFBPs in vitro.

Methods: Serum was incubated with increasing concentrations of six different GAGs (heparin, tinzaparin (Innohep®), dermatan sulfate, heparan sulfate, non-anticoagulant (nac) heparin, and nac low-molecular weight heparin). To investigate for reversibility, heparin was co-incubated with protamine sulfate (PS). Finally, the effect of heparin was studied in serum from pregnant and post partum women, normal subjects and patients with type 1 diabetes.

Results: All GAGs increased free IGF-I in a dose-dependent manner (P < 0.0001), whereas total IGF-I and IGFBP levels remained unchanged. However, the potency of the GAGs differed significantly (P < 0.0001) and did not relate to their anti-coagulating activity. The effect of heparin on free IGF-I was fully reversed by PS. Heparin increased free and bioactive IGF-I in all tested sera (P < 0.0001), but the increase was most pronounced in samples from pregnant women (P < 0.0001).

Conclusion: All tested GAGs stimulated the release of free and bioactive IGF-I in several types of serum, most likely by reversible interaction with the IGFBPs. The effect was most pronounced in pregnancy sera, which are characterized by extensive IGFBP-3 proteolysis. Our findings support the view that GAGs localized in the vessel wall and attached to the extracellular matrix control IGF-I tissue accessibility and bioactivity.

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Birgitte Nellemann, Britt Christensen, Kristian Vissing, Line Thams, Peter Sieljacks, Mads Sørensen Larsen, Jens Otto Lunde Jørgensen and Søren Nielsen


Very low density lipoprotein triglyceride (VLDL–TG) and free fatty acids (FFA) constitute a substantial proportion of human energy supply both at rest and during exercise. Exercise acutely decreases VLDL–TG concentration, and VLDL–TG clearance is increased after an exercise bout. However, the effects of long-term training are not clear.


The aim was to investigate long-term effects of training by direct assessments of VLDL–TG and palmitate kinetics and oxidation in healthy lean men (n=9) at rest, before and after a 10-week training program, compared with a non-training control group (n=9).


VLDL–TG kinetics were assessed by a primed constant infusion of [1-14C]VLDL–TG, and VLDL–TG oxidation by specific activity (14CO2) in expired air. The metabolic study days were placed 60–72 h after the last exercise bout.


Palmitate kinetics and oxidation were assessed by a 2 h constant infusion of [9,10-3H]palmitate. In the training group (n=9), maximal oxygen uptake increased significantly by ≈20% (P<0.05), and the insulin sensitivity (assessed by the hyperinsulinemic–euglycemic clamp) improved significantly (P<0.05). Despite these metabolic improvements, no changes were observed in VLDL–TG secretion, clearance, or oxidation or in palmitate kinetics.


We conclude that 10 weeks of exercise training did not induce changes in VLDL–TG and palmitate kinetics in healthy lean men.