Chromium chloride increases insulin-stimulated glucose uptake in the perfused rat hindlimb
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Chromium has been reported to increase glucose clearance in insulin resistant and diabetic populations. Skeletal muscle is the tissue primarily responsible for glucose clearance. We therefore tested the effect of chromium chloride (CrCl3) on skeletal muscle glucose uptake both in the absence and presence of a submaximal level of insulin via the rat hindlimb perfusion technique. 0.096 μM CrCl3 was used with and without 200 μU/ml insulin. Our testing showed that insulin significantly increased [H3]-2 deoxyglucose (2-DG) uptake in both the gastrocnemius and quadriceps muscles. Additionally, the combination of CrCl3 and insulin (Cr-sIns) led to greater amounts of 2-DG uptake than insulin alone (sIns) in both the gastrocnemius (Cr-sIns 6.49±0.75 μmol/g/h, sIns 4.83±0.42 μmol/g/h) and quadriceps (Cr-sIns 6.74±0.62 μmol/g/h, sIns 4.54±0.43 μmol/g/h). However, CrCl3 without insulin (Cr) had no affect on 2-DG uptake above basal (Bas) in both the gastrocnemius (Cr 1.45±0.14 μmol/g/h, Bas 1.61±30 μmol/g/h) and the quadriceps (Cr 1.35±0.15 μmol/g/h, Bas 1.27±0.13 μmol/g/h). It has been speculated that chromium works to increase glucose uptake by increasing insulin signaling. To examine this, we used western blotting analysis to test both Akt and AS160 phosphorylation in the mixed gastrocnemius. We found that insulin increased Akt and AS160 phosphorylation, but chromium had no affect on Akt (Cr-sIns 25%±2%, sIns 22%±4%) or AS160 (Cr-sIns 35%±5%, sIns 36%±4%) phosphorylation in the absence or presence of insulin. Our results suggest that supplementation with CrCl3 can lead to an increase in glucose uptake in skeletal muscle, but only in the presence of insulin. However, this effect of CrCl3 does not appear to be a result of enhanced insulin signaling.