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At least 1,063 records · Page 59Linked to original sources
PubMed1976

Investigations on metabolic modulation of p-aminohippurate accumulation by rabbit renal cortical slices.

Preparation and incubation of renal cortical slices from adult, female, New Zealand white rabbit depleted tissue citrate concentration. Acetate (10.0 mM) in the incubation significantly increased slice citrate concentration and p-aminohippurate (PAH) accumulation. Physiological concentrations of citrate increased PAH accumulation and final medium pH. increasing concentrations of citrate produced a biphasic effect on PAH accumulation. These data suggested that citrate may act as an intracellular modulator of organic anion transport. This hypothesis was tested with other stimulators of PAH accumulation. Physiological concentrations of alpha-ketoglutarate or succinate increased slice accumulation of PAH. Higher concentrations of either substrate significantly inhibited PAH accumulation. Final medium pH increased with increased medium concentration of both substrates. alpha-Ketoglutarate (0.5 mM) increased PAH accumulation but had no effect on slice citrate concentration. Glucose did not alter either PAH accumulation or slice citrate concentration. Slices incubated without substrate were depleted of citrate but not of alpha-ketoglutarate. Acetate (1.0 mM) significantly increased slice concentration of both alpha-ketoglutarate and citrate. These data suggested that organic anion transport could be modulated by several metabolic intermediates acting through similar but separate mechanisms.

Acetates↗
PubMed1980

Accumulation of [14C]urate and [3H]PAH in isolated proximal tubular segments of the rabbit kidney.

Segments of rabbit proximal tubules (S1, S2, and S3) were incubated (30 min, 37 degrees C, pH 7.4) in Ringer solution (under O2) containing [14C]urate or [3H]PAH and probenecid, pyrazinoic acid (PZA), urate, or PAH, all at 1 mM. The ratio [14C]urate (counts/min per nanoliter of tubular cell water)/(counts/min per nanoliter of incubation medium) (T/M) reached 2.92 +/- 0.31 (mean +/- SE; n = 15), 6.08 +/- 0.42 (n = 42), and 1.72 +/- 0.31 (n = 14) for S1, S2, and S3 segments, respectively. In these segments the uptake of [3H]PAH was 22.7 +/- 4.6 (n = 19), 133 +/- 18.9 (n = 24), and 66.2 +/- 15.3 (n =0). The accumulation of [14C]urate was saturated at 2 x 10(-4) M in the medium, and that of [3H]PAH at 7 x 10(-5) M in the medium. Secretory transport was saturated at the same bath PAH concentration in perfused tubules. Urate and PAH transports inhibited each other, thus suggesting a common transport mechanism mainly located in the S2 segment. Probenecid was a strong and PZA a weak inhibitor of this transport system.

Aminohippuric Acids↗
PubMed1985

Alloxan stimulates p-aminohippurate uptake in renal basal-lateral membranous vesicles.

In renal basal-lateral membranous vesicles, the probenecid-sensitive p-aminohippurate uptake was stimulated by alloxan. This stimulation of uptake was observed only after a lag period of 15 seconds, and it reached a maximal value after one minute. Stimulation was increased by 1 mM to 5 mM alloxan in a linear fashion. The effect was maximal and constant between 5 mM and 20 mM alloxan. Alloxan affected neither the glucose space of the vesicle nor the rate of transport or diffusion of glutamate, another organic anion. The mechanism of stimulation by alloxan was not clear. Its effect was blocked by the sulfhydryl reagent N-ethylmaleimide and weakly mimicked by H2O2, an oxidizing reagent. However, ninhydrin, a structural analogue of alloxan which reacts with sulfhydryl groups, and glucose, a neutral structural analogue of alloxan, failed to stimulate probenecid-sensitive uptake.

Alloxan↗
PubMed1979

Dependence of p-aminohippurate transport on calcium in canine renal cortical slices.

1. Experiments were conducted on renal cortical slices from sixty-one adult mongrel dogs in order to evaluate the relationship between p-aminohippurate (PAH) transport and calcium. Tissues were found to be viable for at least 180 min.2. PAH uptake and the slice/medium (S/M) concentration ratio increased in normal tissues from 3 to 90 min whether data were expressed on a tissue weight or protein content basis. PAH uptake increased with time in calcium-depleted tissues, but all values were lower than normal. At 90 min, PAH S/M in calcium-depleted tissues (4.20 +/- 0.18) was reduced 40% compared to normal tissues (6.90 +/- 0.23).3. Over the time period of 3-90 min incubation, protein concentration ranged from 89.4 to 99.4 mg/g cortex in calcium-depleted tissues. During the same time period in normal tissues, protein concentration ranged from 105 to 117.6 mg/g cortex. No change was observed in medium protein concentration of calcium-depleted tissues.4. Lineweaver-Burke analysis showed similar values for K(m) in normal and calcium-depleted tissues (0.45-0.50 mumole ml.(-1)) although V(max) fell from control values of 0.082 to 0.052 mumole g(-1) min(-1) during calcium depletion.5. After 90 min incubation, addition of EGTA (7, 14 or 21 x 10(-3)M) to media containing calcium was associated with decreased S/M and uptake rates compared to control values from the same animals. The decreases observed were similar to those seen in tissues incubated in calcium-free media.6. Increased cell volume in the presence of calcium was not associated with decreased PAH uptake. Removal of calcium in association with constant cell volume was associated with reduced PAH uptake. Replacement of calcium, but not magnesium, is associated with a return of uptake to normal rates.7. It is concluded that (a) calcium removal causes increased water uptake into cells, (b) calcium removal causes a reduced V(max), (c) calcium is required for maintenance of intracellular PAH, (d) the effect of calcium on PAH is specific and reversible, and (e) the effect of calcium is not mediated by volume changes.

Aminohippuric Acids↗
PubMed1988

Colorimetry of p-aminohippurate in the presence of sulfamethoxazole.

Colorimetric quantification of p-aminohippurate (PAH), which is helpful in assessment of renal function, is subject to interference from sulfa compounds such as sulfamethoxazole. We were unable to measure serum PAH in two patients receiving a trimethoprim-sulfamethoxazole combination because of interference by the latter with the colorimetric estimation. We found that isoamyl acetate removes sulfamethoxazole from the samples without influencing PAH. The extraction is simple, inexpensive, and reproducible.

Aminohippuric Acids↗
PubMed1981

Uptake of [3H]PAH and [14C]urate into isolated proximal tubular segments of the pig kidney.

Segments of proximal convoluted (PCT) and proximal straight (PST) tubules of minipigs and normal-sized pigs were microdissected (without collagenase treatment) and incubated (30 min, 37 degrees C, pH 7.4) in Ringer solution (under O2) containing [3H]PAH (3.10(-5) M) or [14C]urate (9.10(-5) M) and, in inhibitor studies, probenecid, pyrazinoic acid (PZA), urate or PAH, all at 1 mM. In both strains the uptake of [3H]PAH expressed as means T/M ratio (cpm per ml tissue water/cpm per ml incubation medium) was significantly higher (P less than 0.001) in PCT than in PST. T/M was 34.7 +/- 5.6 (SE) in 34 PCT and 2.4 +/- 0.3 in 24 PST of eight minipigs. In two normal-sized pigs the T/M was 14.1 +/- 3.6 in 15 PCT and 1.4 +/- 0.1 in six PST. Similar results were obtained for [14C]urate. In eight minipigs the T/M was 4.9 +/- 0.5 in 24 PCT and 2 +/- 0.2 in 25 PST. In normal-sized pigs the T/M was 3.8 +/- 0.3 in 35 PCT (five pigs) and 1.9 +/- 0.4 in eight PST (two pigs). In inhibitor studies urate significantly depressed the uptake of [3H]PAH, and unlabeled PAH depressed the uptake of [14C]urate. PZA significantly inhibited the uptake of [14C]urate but not that of [3H]PAH, whereas probenecid had a strong inhibitory effect on the uptake of both compounds. These results suggest that [14C]urate and [3H]PAH are transported by a transport system located mainly in the proximal convoluted tubule. These findings are in contrast to the findings obtained in rabbits in which the transport system of PAH and urate is mainly located in the proximal part of the pars recta.

Aminohippuric Acids↗
PubMed1990

The secretion of organic acids and bases by the ovine fetal kidney.

Excretion of organic acids and bases was studied in twelve fetal sheep aged 120-140 days. There was no significant plasma protein binding of the organic anion, p-aminohippurate (PAH), nor of the organic cation, [14C]tetraethylammonium (TEA). There was a significant amount of acetyl-PAH (20 +/- 3%) in fetal urine but none could be detected in fetal plasma. The fractional excretion of unconjugated PAH was less than one, i.e. there was net reabsorption of 31.7 +/- 3.9% of the filtered load of unconjugated PAH. Since there was no acetyl-PAH in fetal plasma it is concluded that all acetyl-PAH in fetal urine occurred as a result of metabolism of PAH and secretion of the metabolite into the tubular lumen. The rate of excretion of acetyl-PAH in fetal urine varied from 0 to 14.0 micrograms min-1. Thus unconjugated PAH is filtered and there is net reabsorption; in addition, PAH is metabolized and enters the urine via tubular mechanisms. The fractional excretion of PAH was unaffected by I.V. administration of penicillin either acutely or chronically. The clearance of [14C]TEA was significantly greater than the glomerular filtration rate (GFR). The mean fractional excretion of [14C]TEA was 5.4 +/- 0.17. Thus 80.7 +/- 0.63% of the excreted TEA was secreted. The clearance of TEA was related to body weight (P less than 0.001) but the fractional excretion of TEA declined with gestation age, probably because GFR increased at a greater rate than the rate at which the secretory pathways increase their activity. It is concluded that those pathways that excrete organic anions like PAH into the urine mature much later (probably after birth) than those pathways responsible for the tubular secretion of organic bases.

Aminohippuric Acids↗
PubMed1988

Identification and comparison of bile acid-binding polypeptides in ileal basolateral membrane.

Bile acid-binding polypeptides were examined using basolateral membrane vesicles and enterocytes isolated from rat ileum. The uptake of a photolabile taurocholate derivative, (7,7,-azo-3 alpha,12 alpha-dihydroxy-5 beta[3 beta-3H]cholan-24-oyl)-2- aminoethanesulfonate,7,7-azo-TC, in ileal vesicles preloaded with paraaminohippurate (PAH) was stimulated with respect to uptake in unpreloaded vesicles. The PAH-transstimulated uptake of 7,7-azo-TC was inhibited by taurocholate and vice versa. Irradiation of membrane vesicles in the presence of 7,7-azo-TC irreversibly inhibited PAH-transstimulated taurocholate uptake. Photoaffinity labeling of basolateral membrane vesicles directly with [3H] 7,7-azo-TC and separation of proteins by SDS-PAGE revealed incorporation of radioactivity into several polypeptides. Photoaffinity labeling of vesicles in the presence of taurocholate inhibited the labeling of 54,000 and 59,000 mol. wt. polypeptides. The efflux of taurocholate from ileal enterocytes was cis-inhibited by 7,7-azo-TC and transstimulated by PAH. Irradiation of enterocytes in the presence of 7,7-azo-TC inhibited taurocholate efflux greater than the presence of 7,7-azo-TC in the dark. When enterocytes that were irradiated in the presence of [3H] 7,7-azo-TC were fractionated and the resultant basolateral membrane fraction was subjected to SDS-PAGE, incorporation of radioactivity into the 54,000 and 59,000 mol. wt. polypeptides was seen. In contrast, when the brush-border membrane fraction was subjected to SDS-PAGE, greatest incorporation of radioactivity was seen in the previously described 99,000 mol. wt. polypeptide. These studies suggest that 7,7-azo-TC shared transporters with natural bile acid and identified polypeptides that may be involved in bile acid transport across the basolateral membrane and differ from that seen in the brush-border membrane of the ileal epithelial cell.

Affinity Labels↗
PubMed1977

The effect of ascorbic acid on uric acid excretion with a commentary on the renal handling of ascorbic acid.

Under spontaneous conditions in man and dog, very little ascorbic acid is excreted in urine. Ascorbic acid clearance (C ascorbic acid) is promptly augmented when plasma ascorbic acid is increased by intravenous injection. No net tubular secretion of ascorbic acid is demonstrable in either man or dog when plasma ascorbic acid is elevated to levels as high as 12 mg/100 ml in man, and 28 mg/100 ml in the dog. Nevertheless, both in men and the Dalmatian dog, when the glomerular filtration rate (GFR) is decreased, excreted ascorbic acid in relation to the amount filtered is exaggerated so that C ascorbic acid:GFR approaches unity. It is possible that secreted ascorbic acid is masked under ordinary circumstances, with a more significant contribution of secreted ascorbic acid to total urinary ascorbic acid becoming apparent under conditions of low GFR. In man, when the plasma ascorbic acid level is raised to above 6 mg/100 ml, C urate:GFR rises from control value of 0.081 +/- 0.020, to 0.116 +/- 0.026. In both mongrel and Dalmatian dogs an effect of ascorbic acid on urate excretion is not conclusively shown. The uricosuric effect of ascorbic acid in man may be due to competition with uric acid for renal tubular reabsorptive transport. The difference in the metabolism of ascorbic acid in the dog as compared to man may help account for the inconsistent effect of ascorbic acid on uric acid excretion in the dog.

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