Figure 1

Lymph transit is markedly impeded by cooling. (A) Lymph transit time was measured by injecting the marker dye India ink subcutaneously into the hind paw of anaesthetised rats and visually monitoring the time taken to reach the exposed lymphatics in the groin, as indicated by the first evidence of improved visualisation of the vessel wall through greying of the lymph. Data shown as mean ± SEM (P < 0.0001 by unpaired two-tailed t-test or P < 0.001 by non-parametric Mann Whitney test, n = 9 and 7 at mean hind limb temperatures of 33 and 3 °C respectively). (B) Contrast-enhanced camera images taken through a dissecting microscope of a rat groin where blood and lymphatic vessels were surgically exposed. (Ba) Image taken 2 h after injection of India ink into the paw of a rat hind limb where the limb and paw but not the groin were maintained at 3 ± 1 °C. Dye transport was so low that the relatively clear lymphatics were not discerned in the camera image despite being identifiable by eye with the exception of one lymphatic in which there was slight greying (green arrow). (Bb) Image of the same area taken 15 min after hind limb cooling was removed shortly after the image of Ba. The leg temperature was now at 15 °C. Yellow arrows point to lymphatic vessels that are now discernible because of transport of the India Ink dye. The same filter for contrast enhancement was applied to both images. Black arrows in Ba and Bb point to a shadow at a bifurcation region of a blood vessel. The width of the images is 3 mm.