MEASUREMENT OF INTERSTITIAL MUSCLE GLUCOSE AND LACTATE CONCENTRATIONSDURING AN ORAL GLUCOSE-TOLERANCE TEST

To study the relationship between blood flow rate and muscle metabolis m, muscle microdialysis was performed in nine human subjects (5 female s and 4 males) after an oral glucose load (75 g). Two microdialysis pr obes were inserted into the medial femoral muscle for estimation of gl ucose and lactate concentrations in the interstitial fluid, and the mu scle blood flow was measured concomitantly with strain-gauge plethysmo graphy. After subjects fasted overnight, their glucose concentration i n arterial plasma and interstitial fluid was 4.6 +/- 0.13 vs. 3.8 +/- 0.23 mmol/l (P < 0.05), and the corresponding lactate concentrations w ere 0.60 +/- 0.07 vs. 0.83 +/- 0.07 mmol/l (P < 0.05). Muscle blood fl ow was 5.2 +/- 0.7 and 7.5 +/- 1.4 ml . 100 g(-1) . min(-1) (P < 0.05) at 0 and 90 min after oral glucose, respectively. The arterial-inters titial concentration differences of glucose increased after oral gluco se [at 0 min 0.73 +/- 0.24 vs. 2.19 +/- 0.60 mmol/l at 90 min (P < 0.0 01)]. The corresponding values for lactate were -0.23 +/- 0.10 at 0 mi n vs. -0.26 +/- 0.18 mmol/l at 90 min (not significant). The data show that 1) the capillary wall is partly rate limiting for glucose uptake , and 2) after oral glucose, the glucose concentration gradient over t he capillary wall increases despite a limited increase in blood flow r ate, which then mediates similar to 10-20% of total enhancement of glu cose uptake in muscle.