Hydrostatic Pressures in Lymphatic Networks of the Mouse

Current research on the lymphatic system makes nearly exclusive use of mouse models because that species is highly amenable to genetic manipulation. However, the lack of information about intraluminal hydrostatic pressures in mouse lymphatic networks limits the ability of investigators, for both in vivo and ex vivo studies, to interpret key physiological data. The goal of the present study was to provide some of that information for several commonly studied lymphatic vessel networks of young, healthy mice: the superficial cervical lymphatic network, the popliteal afferent network, and the mesentery network.

The servo-null micropressure method was used to measure intraluminal hydrostatic pressures in lymphatic vessels, taking advantage of Prox1-GFP and Prox1-tom mice, expressing eGFP and td-tomato reporters, respectively, in lymphatic endothelium, to visualize entire lymphatic networks and facilitate micropuncture of individual vessels.

New methods were devised for making servo-null pressure measurements under fluorescence illumination. Intraluminal pressures oscillated with the lymphatic contraction cycle, and systolic pressure peaks coincided with lymphatic systole. The largest peaks occurred when contractions of consecutive lymphangions were entrained. In networks with active contractions, the pressure profile was "uphill"; in networks without contractions, the pressure profile was "downhill."

Our results provide essential information about the "normal" values for intraluminal hydrostatic pressures in several of the most commonly studied lymphatic networks of the mouse.