Localization of the renin-angiotensin system components to the skeletal muscle microcirculation

Objectives: Local renin-angiotensin systems have been found in various organs and tissues throughout the body. The studies described here tested the hypothesis that a fully functional renin-angiotensin system exists in the skeletal muscle microvasculature. The purpose of this study was to localize the components and products of the system to the skeletal muscle microvasculature. Methods: The presence of mRNA and protein for renin and angiotensinogen was shown by reverse transcriptase polymerase chain reaction analysis and immunohistochemistry, respectively. Angiotensin II concentration in isolated microvessels was measured by high-performance liquid chromatography separation and radioimmunoassay. Results: Renin and angiotensinogen mRNA was detected from isolated cremaster microvessels. Specific staining for renin and angiotensinogen protein was found throughout the walls of microvessels. The concentration of the angiotensin II in the microvessels (104.3 +/- 18.1 fmol/g) was found to be higher than the concentration of angiotensin II in the plasma (8.7 +/- 1.2 fmol/mL) of the same animals. Also, it was shown that the microvessel angiotensin II concentrations in spontaneously hypertensive rats were higher than in Sprague-Dawley rats. Conclusions: The current study demonstrates that within the skeletal muscle microvessels, the components and products necessary for a local renin-angiotensin system are present, but does not rule out the possibility of interaction between circulating and tissue renin-angiotensin systems.