Evidence for the presence of contractile elements in rat renal medullary vasa recta capillaries

Studies in our laboratory have shown differential regulation of blood flow distribution within the renal medulla. There is morphological evidence that smooth muscle-like structures, known as pericytes, surround the vasa recta capillaries (VRC) in the outer medulla (OM) but presently, it is unclear whether pericytes surround VRC within the inner medulla (IM) Since pericytes are believed to contain contractile elements, they may be involved in the control of blood flow distribution between OM and IM. Studies were carried out in Sprague Dawley rats (200-350g) to determine the presence of a contractile element, smooth muscle α-actin, within renal medullary VRC by immunohistochemistry using specific monoclonal antibodies, and the use of RT-PCR to verify the specificity of the smooth muscle α-actin within isolated medullary VRC at the level of RNA. Using immunohistochemistry, we have determined that the smooth muscle α-actin exists throughout the VRC from the OM and IM. Specific primers for the smooth muscle α-actin used on isolated VRC determined that the mRNA was found within these vessels (verified by Southern Blot and PCR sequencing). These results suggest that VRC within both the OM and IM contain smooth muscle α-actin, which may allow these vessels to control intramedullary blood flow distribution.