Thomas Kahn

Effects of Hypotonic Saline Loading in Hydrated Dog: Evidence for a Saline-induced Limit on Distal Tubular Sodium Transport*

We performed studies on dogs under hydrated conditions, utilizing the rate of free water formation (C(H2O)) as an index of the rate of distal tubular sodium transport. Since C(H2O) could be progressively increased with no evidence of a maximal rate during loading with hypotonic (2.5%) mannitol, it was concluded that there is no limit on distal tubular sodium transport during mannitol loading. In contrast, during hypotonic (0.45%) saline loading C(H2O) rose initially, but as urine flow (V) exceeded 25% of the filtered load C(H2O) attained maximal levels (up to 20% of the filtered load) and remained stable as V increased to 50% of the filtered load. It was concluded that saline loading progressively inhibits proximal sodium reabsorption. Initially, the distal tubule absorbes a large fraction of the proximal rejectate and sodium excretion rises slightly. Eventually, an alteration in distal sodium transport appears which culminates in a maximal rate or transport limit. This distal transport limit provoked by saline loading could not be characterized by a classical Tm as seen with glucose and does not seem to be consequent to high rates of flow through the distal tubule. Regardless of the precise nature of this limit, the major increment in sodium excretion develops during saline loading only after saline alters the capacity of the distal tubule to transport sodium.

Infarction of intestine with massive amyloid deposition in two patients on long-term hemodialysis

Two patients undergoing hemodialysis for 19 and 13 yr, respectively, developed intestinal infarction with extensive amyloid deposits in the muscle layer and blood vessels. In 1 patient the deposit reacted positively with antiserum to beta 2-microglobulin by immunohistochemical stain, and therefore was classified as beta 2-microglobulin in origin. The amyloid protein of the other patient remains unclassified. In patients with gastrointestinal symptoms who have been undergoing hemodialysis for long periods of time, amyloidosis of the intestine should be considered.

Plasma Cell Dyscrasia with Kappa Light-chain Crystals in Proximal Tubular Cells: A Histological, Immunofluorescent, and Ultrastructural Study

This is a case report of a 56-year-old man with plasma cell dyscrasia who presented with proximal tubulopathy manifested as kappa light-chain crystal deposition in the proximal convoluted tubular cells. This was associated with mild cellular damage. The crystals were seen as negative images with the hematoxylin–eosin and periodic acid–Schiff (PAS) stains. They were identified as kappa light-chains by immunofluorescent imaging and confirmed by immunoelectron microscopy. Ultrastructurally, the crystals appear to be located within lysosomes. No deposits of light-chains were seen elsewhere in the kidney biopsy.