Capillary Hemodynamics and Expression of Angiogenic Regulators in Metabolically Different Rat Muscles

Abstract

The capillary networks in skeletal muscles are unique in that they have anastomoses that interconnect the capillaries. It is well known that the capillary density as assessed in cross sections is higher in slow than fast muscles. The differences in capillary density in 3-D, red blood cell velocities (VRBC), and angiogenic regulators in slow vs. fast muscles, however, have not been studied extensively. PURPOSE: The aim of this study was to determine if these capillary parameters are different in slow vs. fast muscles in adult rats. To achieve this goal, we used newly developed methods that enabled the visualization of capillaries in 3-D. METHODS: Female Wistar rats (10-12 wk old) were used. Both the capillaries and anastomoses were observed using newly developed pencil-lens probe intravital microscopy techniques under carefully controlled in situ conditions. Applying virtual test grids superimposed onto stacks of perfectly registered optical images captured by a confocal microscope, we have estimated and compared the capillary volume and VBRC in a slow (soleus) and a fast (superficial region of the lateral gastrocnemius, LGs) muscle. In addition, the expression of angiogenic regulators was measured by real-time PCR. RESULTS: VRBC in both the capillaries and the anastomoses was slower in the soleus than LGs. The number of capillaries and anastomoses was higher, diameters smaller, and tortuosity greater in the soleus than LGs. Consequently, capillary volume was larger in the soleus than LGs. In addition, the expression levels of VEGF, HIF-1alpha, and angiopoietin-1 mRNAs were higher in the soleus than LGs. CONCLUSION: The differences in the microvasculature architecture, VRBC and angiogenic regulators between the soleus and LGs are consistent with the greater oxygen demands of the highly active soleus muscle.