The accumulation of nucleated cells in the vasa recta in acute renal failure has been attributed to intravascular hematopoiesis caused by reduced medullary blood flow. Medullary plasma flow was determined in rats with HgCl2 induced acute renal failure by infusing 125I albumin i.v. for 15 or 30 sec and measuring radioactivity in plasma and the renal papillae. Measurements made 40 to 48 hr after i.v. injection of HgCl2 revealed a significantly raised medullary plasma flow at a time when there were prominent collections of nucleated cells in the vasa recta. Vascular tracer studies using India ink demonstrated that blood flow was maintained in vasa recta which contained nucleated cells. Electron microscopic and histochemical studies showed that these cells were lymphocytes, neutrophils and monocytes, present in approximately the same proportions as in the peripheral blood. It is suggested that the nucleated cells in the vasa recta are not produced within the kidney, but are brought there via the circulating blood. Their accumulation within the vasa recta is unexplained but is unrelated to a reduction in medullary blood flow.
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