A B S T R A C T Renal mass and glomerular filtration rate (GFR) were reduced from normal to approximately 15% of normal in two groups of dogs. One group received a constant salt intake (CSI) throughout the study. The second group was subjected to "proportional reduction" of sodium intake (PRS), a dietary regimen which involved the reduction of sodium intake in exact proportion to the decrement in GFR. In the CSI group, absolute sodium excretion rate (UNaV) remained essentially unchanged as GFR fell, while fractional sodium excretion (FEN.) increased progressively from a mean control value of 0.3% to a final value of 4.4%. In the PRS group, UNaV decreased with each reduction in GFR and salt intake, and FENa remained constant throughout. In a second study, the fraction of serum that previously has been shown to possess natriuretic activity in studies of uremic patients was obtained from a group of uremic dogs on the CSI and from another group on the PRS regimen, and the effects of the fraction was measured on sodium excretion in rats. The serum fractions from the dogs on the CSI regimen produced a significant increase in both UNaV and FENa in the assay rats. The same serum fraction from the dogs on the PRS regimen failed to produce a significant increase in either UNaV or FENa.The data are consistent with the view that (a) The increase in FENa in chronically uremic dogs is dictated by the requirements for external sodium balance and may be prevented by prospective manipulation of salt
AB STRA CT The urine and serum of chronically uremic patients and dogs contain an inhibitor of sodium transport that reduces short-circuit current (SCC) in the toad bladder and produces natriuresis in the rat. The present studies represent an effort to determine whether the same inhibitor is detectable in urine of normal dogs maintained on a sodium intake varying from 3 to 258 meq/day. Observations were made with and without fludrocortisone. The same Sephadex G-25 gel filtration fraction previously shown to contain the "uremic" inhibitor was tested in both the isolated toad bladder and rat bioassay systems. The fraction from dogs maintained on 258 meq sodium plus 0.2 mg fludrocortisone/day consistently inhibited SCC in the toad bladder and induced a natriuresis in the rat (P < 0.001). The fraction from dogs on the same sodium intake without fludrocortisone was also natriuretic (P <0.01) but did not inhibit SCC significantly. In contrast, the fraction from dogs fed 3 meq sodium with fludrocortisone or 91 meq sodium without fludrocortisone had no significant effect in either assay system. Thus, an inhibitor of sodium transport has been found in the urine of nonuremic dogs. Both the degree of natriuresis in the rat and the degree of inhibition of SCC in the toad bladder correlated with the state of sodium balance which ensued in the dog.
Patients with analgesic nephropathy are reported to have a higher risk of atherosclerosis. One possible reason for this is a high incidence of hyperlipaemia in patients with analgesic nephropathy. In a retrospective study, serum cholesterol and serum triglyceride concentrations of patients with analgesic nephropathy and moderately restricted renal function were significantly higher compared to a control group with other renal diseases of similar age and degree of renal insufficiency. Hyperlipaemia in analgesic nephropathy is not explained by end-stage renal failure on one side or protein loss as in nephrotic syndrome on the other side. Some possible mechanisms for hyperlipaemia in analgesic nephropathy are discussed.
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