Minerals and bone-modulating hormones in children on continuous ambulatory peritoneal dialysis

Peritoneal fluxes of minerals and bone-modulating hormones and their impact on corresponding serum levels and bone mineralization in 7 children on continuous ambulatory peritoneal dialysis (CAPD) were studied. Most mass transfer studies revealed modest losses of calcium into peritoneal effluents. Peritoneal losses of phosphorus and magnesium, although substantial, were not sufficient to normalize hyperphosphatemia and hypermagnesemia in most patients. Parathormone and vitamin D metabolites (25-hydroxyvitamin D and 1,25-dihydroxyvitamin D) were readily detectable in peritoneal effluents. Improved bone mineral content, by sequential densitometries, was associated with amelioration of hyperparathyroidism. These data suggest that CAPD in children induces an overall improvement of disturbed mineral metabolism; nevertheless, peritoneal losses of calcium and vitamin D metabolites must be considered and replenished appropriately.

Evidence that platelet buoyant density, but not size, correlates with platelet age in man

Following infusion of 51Cr-labeled autologous platelets into normal subjects, high-density (HD) and low-density (LD) platelet cohorts were isolated by prolonged centrifugation in isosmotic arabino-galactan (Stractan). Specific radio-activity of LD platelets declined rapidly post-infusion (T1/2 = 1.5 days), but specific radioactivity of HD platelets remained constant or increased over a 3--4-day period and gradually declined for 6--7 days thereafter. These differences were exaggerated when platelet cohorts enriched in LD or HD cells by slow centrifugation in high-density albumin were labeled and transfused. Mean survival of a platelet cohort enriched with HD cells was significantly (P less than 0.02) shorter (7.73 days) than that of a cohort enriched with LD cells (9.33) days). In normal subjects treated with aspirin, capacity for thromboxane synthesis was regained more rapidly (P less than 0.05) in LD than in HD platelets. HD and LD platelets differed only slightly in mean volume (HD platelets = 7.57 mu3, LD platelets = 6.87 mu3, 0.05 less than P less than 0.01). We believe the most logical interpretation of these findings is that under normal conditions in man, newly formed platelets are less dense on the average than total platelets and become more dense as they age in the circulation. Thus, specific radioactivity of LD platelets declines rapidly as these platelets move into a more dense compartment and are replaced by newly formed, unlabelled cells; specific radioactivity of HD platelets remains constant or increases as labelled platelets enter this compartment in numbers equal to or greater than the number leaving it at the end of their life span. The similarity in mean volumes of LD and HD platelets suggests that platelet size is unrelated to platelet age under normal conditions.

Glomerular selective permeability to macromolecular neutral dextrans in experimental diabetes

Rats with streptozotocin-induced chronic diabetes mellitus develop a glomerulopathy functionally manifested by proteinuria. The ability of the glomerular capillary wall to retard filtration of macromolecules was examined in 5 chronically diabetic Munich-Wistar rats exhibiting excessive proteinuria (39 +/- 7 mg/24 h, mean +/- SEM) and 5 age-matched normal Munich-Wistar rats without increased proteinuria (4.7 +/- 0.2 mg/24 h). Urinary albumin excretion was not increased in the diabetic rats (2.0 +/- 0.6 mg/24 h vs 1.6 +/- 0.3 mg/24 h) suggesting that the normal net electronegative charge of the glomerular capillary wall was not altered. Fractional clearances of macromolecular neutral dextrans were similar in diabetic and normal rats throughout a wide range of molecular size (18-42 A). Glomerular filtration rate was the same in the two groups of rats (2.77 +/- 0.16 ml/min in diabetics and 2.72 +/- 0.11 ml/min in normals) suggesting that renal haemodynamic factors did not influence fractional clearances of neutral dextrans in diabetic rats. We conclude that the proteinuria exhibited by these chronically diabetic rats is not attributable to alterations of size-selective properties of the glomerular capillary wall, such as increases in the size or the number of pores.

Osmolar influences on urinary acidification and metabolism in the Colombian toad bladder

An increase in the osmolarity of the serosal fluid bathing the isolated toad bladder inhibits sodium transport across the preparation. Opposite effects occur with a decrease in serosal Ringer osmolarity. The present experiments investigate the specificity of these osmolar effects by examining the role of extracellular fluid tonicity on the acidification capacity of the isolated Colombian toad bladder. Acidification, estimated by the reversed short-circuit current (RSCC) developing across the Colombian toad bladder in the absence of sodium transport, was stimulated by serosal hypotonicity and inhibited by serosal hypertonicity of acetazolamide. Changes in the mucosal Ringer tonicity had no effect on RSCC. A direct correlation was found between the acidification process and the rate of oxidation of [14C]pyruvate by quarter-bladders exposed to changes in extracellular fluid osmolarity in the presence of amiloride. The osmolar effects on RSCC may result from changes in cell metabolism.

On the influence of the natriuretic factor from patients with chronic uremia on the bioelectric properties and sodium transport of the isolated mammalian collecting tubule

A gel filtration fraction of urine from patients with chronic renal disease (natriuretic factor) has been shown previously to cause natriuresis in rats and to inhibit sodium transport in the isolated toad bladder. The effect of this fraction on transtubular potential difference and sodium transport was examined on the isolated perfused cortical collecting tubule of the rabbit. A rapid inhibition of potential difference from -22.5 mV to -12 mV (P less than 0.001) was observed when the fraction was applied to the peritubular surface. This effect was accompanied by a decrease in net sodium flux from 6.29 to 3.21 pmol/cm per s (P less than 0.001). Unidirectional fluxes using isotopic sodium revealed that the inhibition of net sodium transport was due to a decrease in flux from the lumen to the peritubular surface, i.e., an inhibition of active sodium transport. There was no change in sodium flux in the reverse direction. These changes were all rapidly reversed by removal of the fraction from the peritubular surface. The addition of the fraction to the lumen had no effect on potential difference or net sodium flux. Control studies using the same fraction from the urine of normal subjects had no effect on any of the parameters studies. Where both a uremic and a normal fraction were sequentially applied to the peritubular surface of the same tubule, inhibition of potential difference was obtained only with the former. In the light of evidence implicating the collecting duct fraction from normal animals, the data are consistent with the view that the natriuretic factor may be biologically important in the regulation of sodium balance via it's regulatory role in active sodium transport in the collecting tubule.

Drugs derived from cannabinoids. 5. delta6a,10a-Tetrahydrocannabinol and heterocyclic analogs containing aromatic side chains

Ten new delta6a,10a-THC analogs with arylalkyl side chains, one with a dimethylaminoalkyl side chain, and six heterocyclic delta6a,10a-THC analogs [8-substituted 5,5-dimethyl-10-hydroxy-2-(2-propynyl)-1,2,3,4-tetrahydro-5H-[1]benzo-pyrano[4,3-c]pyridines] were prepared. They showed pharmacological activity as analgesics, tranquilizers, antihypertensives, and hypnotics and as antisecretory, antiulcer, and antidiarrheal agents. The most potent compounds had either a 1-methyl-4-(4-fluorophenyl)butyl or a 1,2-dimethyl-4-(4-fluorophenyl)butyl side chain.

An inhibitor of sodium transport in the urine of dogs with normal renal function

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 dosium 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 qodium plus 0.2 mg fludrocortisone/day consistently inhibited SCC in the toad bladder and induced a natriuresis in the rat (P less than 0.001). The fraction from dogs on the same sodium intake without fludrocortisone was also natriuretic (P less than 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.

The presence of a natriuretic factor in urine of patients with chronic uremia. The absence of the factor in nephrotic uremic patients

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.

A natriuretic factor in the serum of patients with chronic uremia

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.

Sodium transport in turtle erythrocytes. Apparent stimulation of exchange diffusion by anaerobiosis

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.