title: Minimally invasive quantification of lymph flow in mice and rats by imaging depot clearance of near-infrared albumin.
abstract: There is a lack of available methods to noninvasively quantify lymphatic function in small experimental animals, a necessity for studies on lymphatic system pathophysiology. We present a new method to quantify lymph flow in mice and rats, based on optically monitoring the depot clearance of near-infrared fluorescently labeled albumin and subsequent calculation of removal rate constants (k). BSA was conjugated with Alexa680 NHS ester and remained stable in protein-rich solutions without free dye dissociation. To assess lymph flow, mice or rats were imaged every 30 or 60 min during a 3- to 6-h period following an intradermal injection of 0.5 or 1 μl Alexa680-albumin. Mice were awake between measurements, whereas rats were anesthetized throughout the experiment. The k, a parameter defined as equivalent to lymph flow, was calculated from the slopes of the resultant log-linear washout curves and averaged -0.40 ± 0.03 and -0.30 ± 0.02%/min for control C57BL/6 and C3H mice, respectively. Local administration of the vasoconstrictor endothelin-1 in mice led to a significant reduction in k, whereas overhydration in rats increased k, reflecting the coupling between capillary filtration and lymph flow. Furthermore, k was 50% of wild type in lymphedema Chy mice where dermal lymphatics are absent. We conclude that lymph flow can be determined as its rate constant k by optical imaging of depot clearance of submicroliter amounts of Alexa680-albumin. The method offers a minimally invasive, reproducible, and simple alternative to assess lymphatic function in mice and rats.
authors.affiliation: Department of Biomedicine, Hematology Section, University of Bergen, Jonas Lies Vei 91, Bergen, Norway. tine.karlsen@biomed.uib.no
authors.forename: Tine V
authors.initials: TV
authors.lastname: Karlsen
authors.forename: Emmet
authors.initials: E
authors.lastname: McCormack
authors.forename: Maja
authors.initials: M
authors.lastname: Mujic
authors.forename: Olav
authors.initials: O
authors.lastname: Tenstad
authors.forename: Helge
authors.initials: H
authors.lastname: Wiig
mesh_terms: D000418:Albumins / Q000378:metabolism*; D000818:Animals; D005260:Female; D005456:Fluorescent Dyes; D008196:Lymph / Q000502:physiology*; D008208:Lymphatic System / Q000502:physiology*; D051379:Mice; D019275:Radiopharmaceuticals; D051381:Rats
chemical_list: D000418:Albumins; D005456:Fluorescent Dyes; D019275:Radiopharmaceuticals