Decreased Renal Excretion of Uric Acid Following Diuretic Administration in Rats
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Decreased Renal Excretion of Uric Acid Following Diuretic Administration in Rats Kazumi IWAKI and Yukio YONETANI Shionogi Research Laboratories, Shionogi & Co., Ltd., Fukushima-ku, Osaka 553, Japan Accepted December 19, 1983 Abstract-In order to evaluate the cause of diuretic-induced hyperuricemia which has been well documented in clinical studies, clearance experiments were performed in rats using furosemide and trichlormethiazide. The net flux in the tubular transport of uric acid was reabsorptive, and the fractional excretion of uric acid responded sensitively to the transtubular transport inhibitors, sodium probenecid and pyrazinoic acid. When the hemoconcentration was induced by highly potent doses of test diuretics, the inulin clearance and the fractional excretion of uric acid clearly de creased. The contraction of body fluid produced by intraperitoneal administration of polyethylene glycol resulted in marked decrease of inulin clearance and fractional excretion of uric acid. The decrease of uric acid excretory capacity under the treatment with trichlormethiazide was completely corrected by saline loading. Moreover, no significant change was found in the pyrazinoic acid-suppressible fractional excretion of uric acid between the diuretic-treated rats and the control animals. These studies suggest that furosemide and trichlormethiazide-induced changes in the renal handling of uric acid are mediated by the fluid volume con traction and that the decrease in fractional excretion of uric acid by test diuretics is the result of reabsorptive enhancement of uric acid. Hyperuricemia incident to the treatment the decrease of inulin clearance and the with diuretics is well recognized (1-6), and increase of plasma uric acid level. These obstruction in the renal transport system of results corresponded well to the reports on uric acid has been discussed as the cause clinically observed hyperuricemia induced by (2-6). the diuretics (2-6). Accordingly, the present The transport of uric acid in the mammalian communication contributes to the under kidney involves glomerular filtration, tubular standing of the hyperuricemia-inducing effect reabsorption and tubular secretion, though of diuretics in pharmacological studies with the relative importance of uric acid movement experimental animals. in each direction differs among species (7, 8). The rat is a useful animal for evaluating Materials and Methods drug effects on uric acid excretion because Animals and drug treatments: The drugs the net flux in the tubular excretory transport used were sodium probenecid, pyrazinoic acid of uric acid is reabsorptive, although the (Nakarai Chem.), furosemide, trichlorme fractional excretion of uric acid is obviously thiazide (Shionogi) and polyethylene glycol higher than that in man (9-13). Thus, we 4000 (average molecular weight 3000, Wako utilized rats as the animal for evaluating the Chem.). Sodium probenecid and furosemide action of diuretics on the uric acid transport were prepared in our laboratory from com system. mercially avaiable probenecid (Sigma) and The animals treated with furosemide and furosemide solution for injection (Lasix, trichlormethiazide clearly decreased the Hoechst). Sodium probenecid was dissolved fractional excretion of uric acid, together with in saline. Pyrazinoic acid was dissolved in 0.2 N sodium hydroxide solution, then plasma concentrations of inulin and uric neutralized with hydrochloric acid. Fur acid, the resultant plasma was mixed with osemide and trichlormethiazide were sus 10 volumes of 0.007 N acetic acid, heated for pended in 1 % gum arabic solution. These 2 min in boiling water and then centrifuged. agents were administered at 2 ml/kg of body Inulin concentrations in deproteinized plasma weight. Polyethylene glycol was dissolved at and diluted urine were measured by a a concentration of 0.2 g/ml in water and was fluorometric method adapted from the pro administered at 3 ml/rat. The animals of the cedure described by Vurek and Pegram (14). control group were given saline or 1 % gum Uric acid concentrations in the above arabic solution instead of the test agent. specimens were measured by the fluorometric Experiments were performed on male method described previously (15). Wistar strain rats weighing 270-300 g. Hematocrits were measured in heparinized They were permitted free access to food and microhematocrit tubes. Sodium and potas water until the time of the experiment. The sium in plasma were determined by atomic animal room was maintained at 22-23°C and absorption spectrophotometry, and other illuminated at intervals of 12 hr from 8:00 a.m. components in plasma were determined by a to 8:00 p.m. standard autoanalyzer technique (Technicon In experiments on the effects of diuretics, Autoanalyzer, SMA-MICRO system) in which the animals were housed in metabolism cages chloride, creatinine, urea-nitrogen and protein to measure the change in urine volume and were estimated by the method of Zall et al. deprived of food but not water. Furosemide (16), Chasson et al. (17), Marsh et al. (18) (30 mg/kg, i.p.) and trichlormethiazide (10 and Skeggs and Hochstrasser (19), re mg/kg, p.o.) were administered twice at spectively. 10:00 a.m. and 6:00 p.m. A 24-hr urine was The abbreviations used in this paper are collected after the first administration, and C,n, inulin clearance; PCa, plasma uric acid; then the rats were sacrificed by decapitation UUaV, urine-excreted amount of uric acid; to determine blood components or used for Cu, uric acid clearance; and FELa, fractional clearance studies. The procedures for the excretion of uric acid (C„a/Cin). All data are treatments with sodium probenecid, given as means±S.E. and Student's t-test was pyrazinoic acid and polyethylene glycol are used to assess statistical significance. described in the legend of each figure or table. Results Clearance studies: The rats were anes Effects of transtubular transport inhibitors thetized with sodium pentobarbital (50 mg/ on renal handling of uric acid: First, studies kg, i.p.). Polyethylene catheters were inserted were undertaken to confirm whether the into the left femoral vein for infusion of fluid, inhibitor of renal tubular reabsorption and into the right femoral artery for collection of renal tubular secretion of uric acid in man are blood, and into the urinary bladder for also effective in rats used in the present collection of urine. Next, the animals were clearance experiments. Sodium probenecid placed on a thermostatically controlled heated (100 mg/kg, i.v.) and pyrazinoic acid (50 table to maintain the body temperature at mg/kg, i.v.) were administered just after the 37-38°C and were infused with 0.25% first urine collection. Sodium probenecid sodium chloride solution containing 4% produced marked elevations in the urine mannitol, 1.5% inulin and 0.26% sodium excreted amount, the clearance and the pentobarbital at a flow rate of 1.8 ml/hr. fractional excretion of uric acid compared to After a 60-min equilibration period, con the pre-treatment period. The inulin clearance tinuous 20-min urine collections were taken. and the plasma uric acid level did not change A 0.2 ml arterial blood sample was obtained in the treatment with sodium probenecid at the midpoint of each urine collection period. (Fig. 1A). On the other hand, pyrazinoic acid Analysis: The sampled blood was im produced decreases in the urine-excreted mediately cooled in ice water, then cen amount, the clearance and the fractional trifuged as soon as possible. To determine the excretion of uric acid compared to the pre Fig. 1. Effects of sodium probenecid and pyrazinoic acid on renal handling of uric acid in rats. Sodium probenecid (100 mg/kg) and pyrazinoic acid (50 mg/kg) were administered at 80 min from the tail vein. "P<0 .01 compared with the value during the pre-treatment period (60-80 min). Table 1. Changes of urine volume, hematocrit and blood components in furosemide and trichlorme thiazide-treated rats treatment period. The plasma uric acid level duced significant changes in blood compo slightly elevated in the pyrazinoic acid-treated nents as detailed in Table 1. Plasma uric acid rats, but the inulin clearance did not change level increased in both diuretic-treated in the treatment with pyrazinoic acid (Fig. groups. Moreover, creatinine, urea-nitrogen 1 B). Thus, both transtubular transport in and protein levels in plasma were sig hibitors showed reasonable effects, but all nificantly higher in the drug-treated group parameters did not change in the treatment compared to the control. With respect to the with saline. plasma electrolytes, both drugs did not Effects of furosemide and trichlormethizide change the potassium level, but decreased on blood components and renal handling of the chloride level. Sodium level decreased uric acid: Furosemide (30 mg/kg, i.p.) and only with furosemide treatment. trichlormethiazide (10 mg/kg, p.o.) given Next, clearance studies were performed twice daily, sufficient to produce marked in order to understand changes in the renal diuresis, increased the hematocrit and pro transport of uric acid due to the treatments with both diuretics. As indicated in Fig. 2, body fluid on renal transport of uric acid was the two drugs gave similar results in the studied using rats which had received an clearance experiment. The inulin clearance intraperitoneal administration of polyethylene was lower and the plasma uric acid level was glycol. Fluid loss into the peritoneal cavity higher in the diuretic-treated animals com produced by polyethylene glycol resulted in pared to the control. The urine-excreted a marked rise of the hematocrit at 3 hr after amount, the clearance and the fractional the administration, from 47.8±0.5% in the excretion of uric acid were significantly lower nontreated group to 55.4±0.7% (P<0.01). in the drug-treated animals. In the clearance experiment, the inulin Effect of polyethylene glycol-induced clearance and the urine-excreted amount, the volume contraction on renal handling of uric clearance and the fractional excretion of uric acid: The acute effect of contraction of the acid were lower, and the plasma uric acid Fig.