Renal lymphatic ultrastructure and translymphatic transport

Abstract

Information on the mechanisms of transport across renal lymphatic endothelium in the dog was derived by qualitative and quantitative ultrastructural analyses. Interlobular and intralobular renal lymphatics were studied in dogs with ureteric obstruction and lymphatic ligation, in dogs with lymphatic ligation only, and in dogs with unimpeded lymph and urine flow. Minor differences were detected in the ultrastructural features of lymphatic endothelium among the three groups of animals and between the two types of lymphatics studied within each group. Approximately 5% of the endothelial intracytoplasmic volume was occupied by vesicles, the majority of which were of the small uncoated variety. On an average 65% of these vesicles lay within the cytoplasm, and of the remainder, most were associated with the luminal border. Interendothelial contacts were of three varieties—end-to-end, overlapping, and complexly interdigitating. One-third of these lacked any specialized junctional complexes, whereas about 60% of the identifiable complexes revealed a fascia occludens. The remainder (approximately 10%) possessed fascia adhaerentes. Only 2 examples, out of 240 contacts studied, could be described as open junctions (greater than 50 nm). The conclusions drawn from this study were that (1) interlobular and intralobular renal lymphatics subserve similar functions in lymph formation, (2) at least in the absence of local irritation or trauma, open junctions do not play a significant role in translymphatic transport of fluid and protein, and (3) for poorly diffusible substances the primary pathways into the lymphatic lumen are intravesicular transport and the normal intercellular channels between contiguous cells.