Rapid insulin-mediated increase in microvascular glycocalyx accessibility in skeletal muscle may contribute to insulin-mediated glucose disposal in rats

PLoS One. 2013;8(1):e55399. doi: 10.1371/journal.pone.0055399. Epub 2013 Jan 31.

Abstract

It has been demonstrated that insulin-mediated recruitment of microvascular blood volume is associated with insulin sensitivity. We hypothesize that insulin rapidly stimulates penetration of red blood cells (RBC) and plasma into the glycocalyx and thereby promotes insulin-mediated glucose uptake by increasing intracapillary blood volume. Experiments were performed in rats; the role of the glycocalyx was assessed by enzymatic degradation using a bolus of hyaluronidase. First, the effect of insulin on glycocalyx accessibility was assessed by measuring the depth of penetration of RBCs into the glycocalyx in microvessels of the gastrocnemius muscle with Sidestream Dark-field imaging. Secondly, peripheral insulin sensitivity was determined using intravenous insulin tolerance tests (IVITT). In addition, in a smaller set of experiments, intravital microscopy of capillary hemodynamics in cremaster muscle and histological analysis of the distribution of fluorescently labeled 40 kDa dextrans (D40) in hindlimb muscle was used to evaluate insulin-mediated increases in capillary blood volume. Insulin increased glycocalyx penetration of RBCs by 0.34±0.44 µm (P<0.05) within 10 minutes, and this effect of insulin was greatly impaired in hyaluronidase treated rats. Further, hyaluronidase treated rats showed a 35±25% reduction in whole-body insulin-mediated glucose disposal compared to control rats. Insulin-mediated increases in capillary blood volume were reflected by a rapid increase in capillary tube hematocrit from 21.1±10.1% to 29.0±9.8% (P<0.05), and an increase in D40 intensity in individual capillaries of 134±138% compared to baseline at the end of the IVITT. These effects of insulin were virtually abolished in hyaluronidase treated animals. In conclusion, insulin rapidly increases glycocalyx accessibility for circulating blood in muscle, and this is associated with an increased blood volume in individual capillaries. Hyaluronidase treatment of the glycocalyx abolishes the effects of insulin on capillary blood volume and impairs insulin-mediated glucose disposal.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Analysis of Variance
  • Animals
  • Blood Volume / drug effects
  • Blood Volume / physiology
  • Erythrocytes / physiology
  • Glucose / metabolism*
  • Glycocalyx / metabolism*
  • Hematocrit
  • Histological Techniques
  • Hyaluronoglucosaminidase / pharmacology
  • Insulin / metabolism*
  • Insulin Antagonists / pharmacology
  • Insulin Resistance / physiology
  • Male
  • Microvessels / metabolism*
  • Muscle, Skeletal / blood supply*
  • Muscle, Skeletal / metabolism
  • Rats
  • Rats, Wistar

Substances

  • Insulin
  • Insulin Antagonists
  • Hyaluronoglucosaminidase
  • Glucose

Grant support

The study was supported by the Dutch Diabetes Research Foundation (grant number 2006.00.027), the Netherlands Heart Foundation (grant number 2005T037) and the Center for Translational Molecular Medicine (Work package 01C-104-04-PREDICCT). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.