TOTAL FOREARM BLOOD-FLOW AS AN INDICATOR OF SKELETAL-MUSCLE BLOOD NOW- EFFECT OF SUBCUTANEOUS ADIPOSE-TISSUE BLOOD NOW

1. In studying forearm skeletal muscle substrate exchange, an often ap plied method for estimating skeletal muscle blood flow is strain gauge plethysmography. A disadvantage of this method is that it only measur es total blood flow through a segment of forearm and not the now throu gh the individual parts such as skin, adipose tissue and muscle. 2. In the present study the contribution of forearm subcutaneous adipose ti ssue blood flow to total forearm blood flow was evaluated in lean (% b ody fat 17.0 +/- 2.2) and obese males (% body fat 30.9 +/- 1.6) during rest and during infusion of the non-selective beta-agonist isoprenali ne. Measurements were obtained of body composition (hydrostatic weighi ng), forearm composition (magnetic resonance imaging) and of total for earm (venous occlusion plethysmography), skin (skin blood flow, laser Doppler), and subcutaneous adipose tissue blood flow (Xe-133 washout t echnique). 3. The absolute forearm area and the relative amount of fat (% of forearm area) were significantly higher in obese as compared to lean subjects, whereas the relative amounts of muscle and skin were s imilar. 4. During rest, the percentage contribution of adipose tissue blood flow to total forearm blood flow was significantly higher in lea n compared with obese subjects (19 vs 12%, P < 0.05), whereas there we re no differences in percentage contribution between both groups durin g isoprenaline infusion (10 vs 13%). Furthermore, the contribution of adipose tissue blood flow to total forearm blood now was significantly lower during isoprenaline infusion than during rest in lean subjects (P < 0.05), whereas in the obese this value was similar during rest an d during isoprenaline infusion. 5. In conclusion, although the overall contribution of adipose tissue blood flow to total forearm blood flow seems to be relatively small, the significance of this contribution m ay vary with degree of adiposity. Calculations on the contribution of adipose tissue blood flow and SBF to total forearm blood flow indicate that the contribution of non-muscular flow to total forearm blood flo w may be of considerable importance and may amount in lean subjects to 35-50% of total forearm blood flow in the resting state.