Distribution and density of the canine renal cortical lymphatic system

The pattern, distribution, and extent of the lymphatic circulation in the canine renal cortex was studied with light and electron microscopy, in two groups of animals, one with and one without ipsilateral ureteric obstruction for 3 days. Recognition of lymphatics in tissue sections was facilitated by mild dilatation, induced in both groups by ligation of the renal collecting vessels for 4 to 6 hours, and by retrograde injection of tracer in a third group. Of 77 lymphatics present in 180 blocks from six kidneys, approximately one third were intralobular, the remainder being primarily associated with interlobular blood vessels. The cross-sectional area of interlobular lymphatics was almost twice that of intralobular lymphatics. The relationships of these lymphatics were analyzed quantitatively. Intralobular lymphatics had primary relationships with terminal arteries, arterioles, renal corpuscles, and tubular elements. Both inter- and intralobular lymphatics had secondary relationships with a small proportion of all components of the cortical parenchyma including juxtaglomerular complexes. The most common association was between lymphatics and elements of the vascular tree. Morphometric analysis was used to obtain volume density data on the composition of the renal cortex. The volume density of lymphatics was 0.0026 in ureter-obstructed kidneys and 0.0017 in nonobstructed kidneys. The cross-sectional surface area of lymphatics in ureter-obstructed kidneys was significantly larger than those in nonobstructed kidneys. The volume density of other cortical components was found to be in good agreement with published data. From the volume density data, it was concluded that the volume of lymph in the renal cortex, under conditions of mild lymphatic dilatation, was about 1% that of the volume of blood in the cortical peritubular capillaries.