Contractility and flow in aged mesenteric lymphatic vessels

Effective mesenteric lymph flow is crucial for fluid and macromolecule homeostasis, fat absorption, and immunity. Aging distorts all of these functions, while even the status of contractility and flow in aged mesenteric lymphatic vessels (MLV) is not well characterized. In this study, we investigated the aging‐related changes of contractility and flow in MLV in vivo with reference to their NO‐dependent modulation. We used a high‐speed imaging system to measure flow and diameter of MLV in two age groups of Fischer‐344 rats: 9‐mo and 24‐mo old. A gently exteriorized loop of the small intestine was imaged on a preparation board using an intravital microscope equipped with a digital high‐speed video camera (500 fps). Video files with duration of 1–2 minutes were processed using a combination two techniques: particle image velocimetry ‐ to track moving lymphocytes inside the MLV and particle tracking velocimetry ‐ to track movement of the MLV walls. Changes in lymphatic diameter, frequency of MLV contractions, flow velocity, flow rate and wall shear stress were calculated. Imaging was performed under controlled conditions and during the application of the non‐selective nitric oxide synthase (NOS) inhibitor, L‐NAME. Results demonstrate the negative inotropic and chronotropic effects of aging on contractility of MLV including their differential responses to NOS blockade for both age groups. NIH R01 AG030578, HL094269.