An integrated light and electron microscopic study on the existence of intramedullary lymphatics in the dog kidney.

The existence of intramedullary lymphatics was investigated in canine kidneys by two detailed morphological approaches. The first used a combined light and electron microscopic analysis of medullary tissue fixed in vivo and obtained from animals with dilated as well as freely-flowing intrarenal lymphatics. Examination of 100 vascular bundles and 100 interbundle areas from 90 medullary tissue strips elicited only one strip containing lymphatic vessels. These lymphatics, in a vascular bundle, were confirmed ultrastructurally and were followed in serial one micron sections which revealed their course to be immediately adjacent to or within the arcuate region. The dearth of medullary lymphatics was in marked contrast to the existence of cortical lymphatics found in similarly processed tissue. By the second approach sections of arcuate lymphatics were examined for medullary tributaries. In serial sections from 60 tissue blocks arcuate lymphatics received only cortical tributaries. Reconstruction diagrams made from 8 blocks showed 14 tributaries from the cortex and none from the medulla. It was concluded from this study that an intramedullary system of lymphatics does not exist within the dog kidney. It is proposed that a meduallary contribution to renal lymph occurrs by movement of fluid through the medullary interstitium to lymphatics associated with arcuate or possibly interlobar blood vessels.