The Regulation Of Subcutaneous Adipose Tissue Blood Flow During Exercise In Humans

Abstract

Adipose tissue blood flow in humans has been rather sparsely studied, especially in response to exercise. In a recent study Stallknecht and colleagues showed evidence of increased blood flow in subcutaneous adipose tissue (SCAT) adjacent to exercising compared to resting muscle by use of xenon-washout technique (Stallknecht et al. Am J Physiol Endocrinol Metab. 292:E394-399, 2007). PURPOSE: In the present study we investigated whether SCAT blood flow increases along with increasing exercise intensity and tested the hypothesis that adenosine plays a role in the regulation of SCAT during exercise. METHODS: We measured SCAT blood flow at rest and during exercise with increasing exercise intensities with positron emission tomography (PET) and [15O]H2O in six healthy young women. Exercise consisted of intermittent isometric knee extensor contractions (1 s contraction followed by 2 s rest with workloads of 50, 100, and 150 N). Adipose tissue blood flow was measured adjacent to working knee-extensors (QF) and adjacent to inactive hamstring muscles localised based on the fused images of PET and MRI. Measurements were performed without and with non-specific adenosine receptor blockade by intravenous infusion of theophylline. RESULTS: SCAT blood flow adjacent to working QF increased from rest (1.0 ± 0.3 ml/100g/min) to exercise with increasing exercise intensity (50N = 4.1 ± 1.4 ml/100g/min, 100N = 5.4 ± 1.8 ml/100g/min and 150N = 6.9 ± 3.0 ml/100g/min, p = 0.03), while blood flow in subcutaneous adipose tissue adjacent to inactive muscle remained essentially the same to rest (1.0 ± 0.5 ml/100g/min) and during three exercise intensities (1.2 ± 0.8, 0.9 ± 0.3, and 0.9 ± 0.3 ml/100g/min). Theophylline prevented the increase in SCAT blood flow adjacent to working muscle towards the highest exercise intensity (4.3 ± 1.8, 4.0 ± 1.5, and 4.9 ± 1.8 ml/100g/min, respectively, p = 0.06), but had no significant effect on adipose blood flow adjacent to inactive muscle (1.6 ± 1.0, 1.1 ± 0.1, and 1.1 ± 0.5 ml/100g/min). CONCLUSIONS: The results show that SCAT blood flow adjacent to working muscle increases with increasing exercise intensity and that this increase is partly mediated by adenosine.