Insulin selectively increases accessibility of small dextrans in capillaries of rat skeletal muscle: role for glycocalyx

Abstract

ObjectiveTo determine the effect of insulin on solute accessibility in skeletal muscle capillaries and the role of the glycocalyx herein.MethodsA bolus of small (40 kDa) dextrans (dex40) and large (2000 kDa) dextrans (dex2000) was i.v. infused in anesthetized rats (control versus hyaluronidase, during rest and 30 minutes after a bolus of insulin (1U/kg); all N=3). 3 minutes after tracer infusion the calf muscle was removed, formaldehyde‐fixed, paraffin‐embedded and sectioned. Images were captured using fluorescence microscopy. For each dextran, the total intensity per mm2 muscle was calculated from the number of tracer filled capillaries multiplied by the average intensity of each tracer per capillary.ResultsTotal intensity of Dex40 did not differ between control and hyaluronidase treated rats (70276 ± 5416 versus 95500 ± 43041) (MEAN ± SEM) in rest, but was increased after insulin in all experiments (control: 103991 ± 7787, hyaluronidase: 190147 ± 47995). Total intensity of Dex2000 did also not differ between control (45744 ± 10730) and hyaluronidase treated rats (31061 ± 2512) at rest. In contrast to Dex40, only an increase after insulin in the hyaluronidase treated rats was observed.ConclusionThese data indicate that insulin facilitates the selective delivery of small‐sized plasma solutes in capillaries of skeletal muscle. The size‐selectivity is lost after enzymatic glycocalyx degradation.Sponsored by Dutch Heart Foundation (NHS2009B56) and Dutch Diabetes Research Foundation (DFN 2006.00.027)