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A gel filtration fraction of serum from chronically uremic patients has been shown previously to produce natriuresis in the rat. In the present studies, the same fraction from urine of uremic patients and normal subjects was studied for its natriuretic activity. Urine samples were obtained from 17 chronically uremic patients (mean glomerular filtration rate [GFR], 8.7 ml/min; mean fractional sodium excretion [FE(Na)], 5.7%), and 14 normal subjects. The fraction from the uremic patients produced a significant increase in absolute sodium excretion (U(Na)V) and FE(Na); the fraction from normal subjects had no statistically significant effect on either U(Na)V or FE(Na); and the difference between the response to the uremic vs. normal fractions was highly significant for both parameters of sodium excretion. When a more concentrated urine fraction from uremic patients was administered, a striking natriuresis was observed with values for FE(Na) rising to levels as high as 12%. Studies also were performed on eight patients with far advanced chronic renal insufficiency and the nephrotic syndrome. The serum fraction was studied in each of these patients and the urine fraction in three. For the group, U(Na)V in the assay rats decreased by 0.87 mueq/min and FE(Na) decreased by 1.35% after infusion of the serum fraction. These results differ significantly from those of patients with chronic uremia without the nephrotic syndrome. The data are consistent with the view that the increased activity of the natriuretic factor in the serum of chronically uremic patients is not due to failure of excretion; rather it relates either to an increased rate of production and/or a decreased rate of degradation. The data also show that the inhibitor is detectable when FE(Na) is increased, but not when uremia is associated with a sodium-retaining state.

Inhibitors of protein synthesis capable of differential effects on nascent peptide synthesis on membrane-bound and free polyribosomes were employed to investigate the structure and function of cellular membranes of liver. The formation of membranous whorls in the cytoplasm and distension of nuclear membranes were induced by inhibitors of protein synthesis (i.e., cycloheximide and emetine) which predominantly interfere with nascent peptide synthesis on membrane-bound polyribosomes in situ. Other inhibitors of protein synthesis such as puromycin and fusidic acid, which inhibit nascent peptide synthesis on both free and membrane-bound polyribosomes, and chloramphenicol, which inhibits mitochondrial protein synthesis, did not induce these alterations. Cycloheximide, puromycin, and chloramphenicol produce some common cellular lesions as reflected by similar alterations in morphology, such as swelling of mitochondria, degranulation of rough endoplasmic reticulum, and aggregation of free ribosomes. The process of whorl formation in the cytoplasm, the incorporation of [(3)H]leucine and of [(3)H]choline into endoplasmic reticulum and the total NADPH-cytochrome c reductase activity of the endoplasmic reticulum were determined. During maximum formation of membranous whorls, [(3)H]leucine incorporation into cytoplasmic membranes was inhibited, while [(3)H]choline incorporation into these structures was increased; maximum inhibition of protein synthesis and stimulation of choline incorporation into endoplasmic reticulum, however, preceded whorl formation. Cycloheximide decreased the activity of NADPH-cytochrome c reductase of rough endoplasmic reticulum, but increased NADPH-cytochrome c reductase activity of smooth endoplasmic reticulum. In addition, cycloheximide decreased the content of hemoprotein in both the microsomal and mitochondrial fractions of rat liver, and the activities of mixed function oxidase and of oxidative phosphorylation were impaired to different degrees. Succinate-stimulated microsomal oxidation was also inhibited. The possible mechanisms involved in the formation of membranous whorls, as well as their functions, are discussed.

Studies were performed on Na and K transport by red blood cells of the freshwater turtle under anaerobic and aerobic conditions. Although it had previously been assumed that cation transport in turtle red blood cells was dependent on respiration, the present data show greater Na efflux rates in N(2) than in O(2). However, ouabain inhibited Na transport by the same amount quantitatively in O(2) and N(2) gas phases. Thus there was no difference in ouabain-sensitive or "pump" Na transport rates. Na influx rates were higher in nitrogen than in air and potassium influx rates were not significantly different under aerobic and anaerobic conditions. Moreover in the absence of sodium in the bathing medium no difference between air and nitrogen could be discovered. Finally with ethacrynic acid plus ouabain there was an additional decrease in Na efflux but there was a persisting difference between air and nitrogen. These studies do not rule out the existence of a ouabain-insensitive ethacrynic acid-inhibitable flux; however, they suggest that at least part of the activation of Na efflux observed in N(2) was due to increased exchange diffusion.

Sera from chronically uremic and normal individuals were subjected to gel filtration with Sephadex G-25 and the same fraction of both was infused into rats with a decreased nephron population to determine the effects on sodium excretion. Sodium excretion rate and fractional sodium excretion increased slightly with the normal fractions; but the increase in both functional parameters produced by the uremic fractions was substantially and significantly greater. The natriuresis could not be explained by associated changes in glomerular filtration rate (GFR), para-aminohippurate (PAH) clearance, filtration fraction, hematocrit, or blood pressure. The possibility thus exists that the inhibitor affected some component part of the transepithelial sodium transport system. The elution characteristics of the fraction plus certain of its physicochemical properties suggest that the inhibitor of sodium reabsorption by the rat nephron may be identical with the inhibitor of PAH uptake by kidney slices and the inhibitor of transepithelial sodium transport by the frog skin and toad bladder previously found in the serum of chronically uremic patients.