Roles of histamine, complement and xanthine oxidase in thermal injury of skin

The pathogenesis of burn edema in the skin of rats appears to be related to a role for histamine, xanthine oxidase and oxygen radicals. Histamine and its metabolic derivatives increase the catalytic activity of xanthine oxidase (but not xanthine dehydrogenase) in rat plasma and in rat pulmonary artery endothelial cells. In thermally injured rats levels of plasma histamine and xanthine oxidase rise in parallel, in association with increases in uric acid. Burn edema is greatly attenuated by treatment of rats with the mast cell stabilizer, cromolyn, by complement depletion and by treatment with the H2 receptor antagonist, cimetidine, but is unaffected by neutrophil depletion. These studies suggest the following pathogenesis of burn edema: thermal trauma causes complement activation with anaphylatoxin release and mast cell secretion of histamine, leading to enhancement of xanthine oxidase activity and increased production of oxygen radicals which damage endothelial cells.

[Effect of tranquilizers of the 1,4-benzodiazepine series on the xanthine oxidase activity of the rat brain]

Experiments in vivo and in vitro on 90 rats were made to study the influence of 1,4-benzodiazepine tranquilizers (phenazepam, nitrazepam and diazepam) on cerebral xanthine oxidase activity. Phenazepam, nitrazepam and diazepam in the dose of 5 mg per 200 g bw were shown to reduce xanthine oxidase activity by 80.4%, 64.3% and 55.8%, respectively 2 h after intraperitoneal injection. 6 h after the injection of benzodiazepines the enzyme activity grows, but control values are achieved only after nitrazepam injection. In vitro experiments revealed direct influence of the tranquilizers on xanthine oxidase. Phenazepam inhibits xanthine oxidase activity in concentration as long as 10(-10) M (to 36.6%), and practically completely in 10(-6) M concentration. Nitrazepam and diazepam inhibit xanthine oxidase activity within concentration range between 10(-8) M (to 51.5% and 33.2%, respectively), and 10(-4) M (practically completely). The inhibition of xanthine oxidase activity is shown to be caused by the competition between hypoxanthine, the reaction substrate, and tranquilizer, to bind with the active site of the enzyme.

Inherited superactivity of phosphoribosylpyrophosphate synthetase: association of uric acid overproduction and sensorineural deafness

PURPOSE

Superactivity of 5-phosphoribosyl 1-pyrophosphate (PP-Rib-P) synthetase, inherited as an X chromosome-linked trait, has been reported in nearly 20 families in which overproduction of uric acid is invariably present in hemizygous affected males. Clinical manifestations of PP-Rib-P synthetase superactivity are mainly limited to gout in early adulthood. Neurologic deficits, including sensorineural deafness, have rarely been described. We herein document the association of PP-Rib-P synthetase superactivity, gout with excessive uric acid synthesis, and sensorineural deafness in an additional family.

PATIENTS AND METHODS

Two members of a Spanish family were studied: an eight-year-old boy (Patient 1) with tophaceous gout, purine nucleotide and uric acid overproduction, and sensorineural deafness, and his 27-year-old mother (Patient 2), who had gout. Fibroblast cultures were initiated from skin biopsy specimens, and measurements of PP-Rib-P and purine nucleotide metabolism in the fibroblasts were performed.

RESULTS

A labile but superactive PP-Rib-P synthetase was demonstrated in the fibroblasts cultured from both Patients 1 and 2. The kinetic basis of PP-Rib-P synthetase superactivity in this family was resistance to purine nucleotide inhibition of enzyme activity. More severe derangements in the enzyme and in PP-Rib-P and purine synthesis in Patient 1's cells than in Patient 2's cells suggest that Patient 1 is hemizygous and Patient 2 is heterozygous for an X chromosome-linked genetic defect. Limited pedigree data support this view. Compared with affected members of seven other families with PP-Rib-P synthetase superactivity, these patients are intermediate in the range of clinical expression and in the severity of the enzyme defect as measured by the degree of aberration of PP-Rib-P and purine nucleotide synthesis in fibroblasts. Metabolic abnormalities were more severe in Patient 1's cells than in the cells of most male patients (in whom clinical expression is limited to early adult-onset gout) but were less severe than in the cells of two patients in whom more complex enzyme defects were associated with uric acid overproduction and neurodevelopmental abnormalities (including deafness) in male children and adult women.

CONCLUSION

Certain defects resulting in PP-Rib-P synthetase superactivity may be causally related to neurologic impairment, most commonly sensorineural deafness.

Copper(II)ethylenediaminetetraacetate does disproportionate superoxide

The superoxide dismutase (SOD) mimetic reactivity of Cu(II)EDTA was studied in the pH range of 6.0 to 8.0. Cu(II)EDTA disproportionated superoxide without inhibiting superoxide production by xanthine oxidase, as a result of bonding sites becoming available on the copper complex with increasing acidity. This disproportionation by Cu(II)EDTA is offered as evidence that the addition of EDTA to biological preparations for the purpose of complexing copper and thereby inhibiting copper-dependent superoxide disproportionation and promoting superoxide-dependent reactions is not a valid practice.

Increase of urate formation by stimulation of sympathetic hepatic nerves, circulating noradrenaline and glucagon in the perfused rat liver

In the isolated rat liver perfused in situ stimulation of the nerve bundles around the portal vein and the hepatic artery caused an increase of urate formation that was inhibited by the alpha 1-blocker prazosine and the xanthine oxidase inhibitor allopurinol. Moreover, nerve stimulation increased glucose and lactate output and decreased perfusion flow. Infusion of noradrenaline had similar effects. Compared to nerve stimulation infusion of glucagon led to a less pronounced increase of urate formation and a twice as large increase in glucose output but a decrease in lactate release without affecting the flow rate. Insulin had no effect on any of the parameters studied.

Purine synthesis de novo in cultured lymphoblast cells derived from patients with gout

Rates of de novo purine synthesis in lymphoblast cell cultures derived from ten patients with gout were compared with those from control individuals. Since the growth rate of the culture, an assay procedure was developed to account for the variation in lymphoblast growth rates and to permit valid quantitative comparison between purine synthesis in each cell line. Clear differences were demonstrated between the rates of purine synthesis in cells from normal control subjects and those from patients with a deficiency of hypoxanthine-guanine phosphoribosyltransferase activity (HPRT-deficient). Lymphoblasts from the gouty patients showed purine synthesis either within the normal range or intermediate between this and the HPRT-deficient cells. In patients having normal renal function, de novo purine synthesis of lymphoblast cells correlated with the degree of urate production as reflected by the urinary excretion of urate over a 24 h period. Three patients, with demonstrable excessive production of urate in vivo, exhibited increased purine synthesis in lymphoblasts. This increased synthesis did not appear to result from any of the enzyme mutations currently recognized as responsible for abnormal purine metabolism.

Oral zinc therapy normalizes serum uric acid level in Wilson's disease patients

The authors investigated changes in the serum uric acid (s-UrA) level seen in a Wilson's disease patient who had to undergo oral zinc therapy because of the occurrence of D-penicillamine-induced acute sensitivity reactions, including neutrophilic agranulocytosis, thrombocytopenia, and skin eruptions. Although s-UrA levels were low before oral zinc therapy (mean +/- SD, 1.60 +/- 0.20), they increased (mean +/- SD, 2.63 +/- 0.32) to within normal range (2.8-8.0 mg/dl) after therapy. There were no significant changes in the renal tubular reabsorption of UrA during oral zinc therapy. This therapy also produced an improvement of the decreased cholinesterase (ChE) values usually seen in Wilson's disease. These results suggest that oral zinc therapy can normalize UrA metabolism in Wilson's disease by improving liver dysfunction and increasing UrA synthesis.

Allopurinol in renal failure and the tumour lysis syndrome

This paper illustrates several important points relating to the use of allopurinol in renal failure, or situations of purine overproduction: It is very easy to give too much allopurinol. Most of the side effects (bone marrow depression, exfoliative dermatitis, etc) are the result of overdosage due to the retention of oxipurinol, an effect exaggerated by thiazide diuretics. Monitoring of plasma oxipurinol levels (ideally less than 100 mumol/l) by high-pressure liquid chromatography is helpful for adjusting dosage in renal failure. Some estimate of the anticipated purine excess is equally vital in deciding dosage during tumour lysis if the risk of urate nephropathy is not to be substituted for the certainty of xanthine nephropathy. In this situation the use of allopurinol may even be questioned. Patients with HGPRT deficiency are exquisitely sensitive to allopurinol, and careful monitoring of the effect on urinary purine levels is essential if xanthine colic is to be avoided.

In vivo voltammetric evidence of production of uric acid by rat caudate

Linear sweep in vivo voltammetry with carbon paste electrodes records a prominent peak at about 340 mV in the anterior caudate of rat brain. This peak is increased by microinfusion of uric acid or xanthine oxidase (which enhances conversion of hypoxanthine and xanthine to uric acid) and is decreased or eliminated by microinfusion of uricase. Allopurinol (a specific xanthine oxidase inhibitor) also decreases this peak when given either intracranially or intraperitoneally. Co-administration of uricase and allopurinol reliably eliminate the peak in question. These data suggest that uric acid, a purine metabolite that has been thought to be absent in brain, is formed locally in rat caudate and that uric acid is the sole component of the peak at 340 mV. In vivo voltammetry may be a useful new tool for studying brain purine metabolism.

Hyperuricemia in glycogen storage disease type I. Contributions by hypoglycemia and hyperglucagonemia to increased urate production

Studies were performed to determine whether hypoglycemia or the glucagon response to hypoglycemia increases uric acid production in glycogen storage disease type I (glucose-6-phosphatase deficiency). Three adults with this disease had hyperuricemia (serum urate, 11.3-12.4 mg/dl) and reduced renal clearance of urate (renal urate clearance, 1.1-3.1 ml/min). These abnormalities were improved in one patient by intravenous glucose infusion for 1 mo, suggesting a role for hypoglycemia and its attendant effects on urate metabolism and excretion. A pharmacologic dose of glucagon caused a rise in serum urate from 11.4 to 13.0 mg/dl, a ninefold increase in urinary excretion of oxypurines, a 65% increase in urinary radioactivity derived from radioactively labeled adenine nucleotides, and a 90% increase in urinary uric acid excretion. These changes indicate that intravenous glucagon increases ATP breakdown to its degradation products and thereby stimulates uric acid production. To observe whether physiologic changes in serum glucagon modulate ATP degradation, uric acid production was compared during saline and somatostatin infusions. Serum urate, urinary oxypurine, radioactivity, and uric acid excretion increased during saline infusion as patients became hypoglycemic. Infusion of somatostatin suppressed these increases despite hypoglycemia and decreased the elevated plasma glucagon levels from a mean of 81.3 to 52.2 pg/ml. These data suggest that hypoglycemia can stimulate uric acid synthesis in glucose-6-phosphatase deficiency. Glucagon contributes to this response by activating ATP degradation to uric acid.

The use of xanthine oxidase for a specific and sensitive fluorimetric determination of 6-mercaptopurine in serum

A specific and highly sensitive fluorimetric method was developed for the determination of 6-mercaptopurine (6MP) in serum. The method is based on the enzymatic oxidation of 6MP with xanthine oxidase to the oxypurine, followed by oxidation with acidic chromate to the corresponding 6-sulfonate. The fluorescent product has excitation and emission maxima at 330 and 400 nm, respectively. The limit of sensitivity was approximately 22 pg/ml for 6MP in water. The sensitivity limit for 6MP in serum containing azathioprine was approximately 2.2 ng/ml. The rate constants for conversion of 6MP into the final product (6-thiouric acid) and the apparent Michaelis constant were also determined by a nonlinear regression analysis based on the integrated Michaelis-Menten equation using the ultraviolet absorbance data and the simplified complementary tristimulus colorimetry.

Purine metabolism in high and low uric acid lines of chickens: de novo uric acid synthesis in isolated hepatocytes and phosphoribosylpyrophosphate amidotransferase activities

The de novo biosynthesis of uric acid was examined in isolated hepatocytes from the high and low uric acid lines of chickens. Rates of incorporation of radiolabeled glycine into uric acid by hepatocytes from the high uric acid (HUA) line were approximately 3.6-fold greater than found in low uric acid (LUA) control hepatocytes. Uric acid synthesis rates in these cells were positively correlated with plasma uric acid levels (r = +0.77; P less than 0.01). The activity of phosphoribosylpyrophosphate (PRPP) amidotransferase was measured in acetone powder preparations from liver and kidney tissues of the HUA and LUA lines. Activities in kidney tissues were about 21% lower than those found in livers. PRPP amidotransferase activities in liver and kidney tissues did not correlate significantly with plasma uric acid levels. The increased synthesis of uric acid in the HUA line may be the result of the increased PRPP synthetase activities and PRPP pool sizes previously reported for these tissues.

Purine metabolism and urate biosynthesis in isolated chicken hepatocytes

The metabolism of some purine compounds to urate and their effects on de novo urate synthesis in chicken hepatocytes were investigated. The purines, listed in descending order of rates of catabolism to urate, were hypoxanthine, xanthine, inosine, guanosine, guanine, IMP, GMP, adenosine, AMP, and adenine. During a 1-h incubation period, conversion to urate accounted for more than 80% of the total quantities of guanine, guanosine, and inosine metabolized, but only 42% of the adenosine and 23% of the adenine metabolism. Adenine, adenosine, and AMP inhibited de novo urate synthesis [( 14C]formate incorporation into urate), whereas the other purines, especially guanine, guanosine, and GMP, stimulated de novo urate synthesis. When hepatocytes were incubated with glutamine and adenosine, AMP, guanine, guanosine, or GMP, the rates of de novo urate synthesis were lower than the additive effects of glutamine and the purine in separate incubations. Increasing phosphate concentrations had no effect on urate synthesis in the absence of added purines but, in combination with adenosine, AMP, guanosine, or GMP, increased urate synthesis. These results indicate that the ratio of adenine to guanine nucleotides and the interaction between substrates and purine nucleotides are involved in the regulation of urate biosynthesis in chicken liver.

Incorporation of 15N from glycine into uric acid in gout: a follow-up study

Over-incorporation of 15N-labeled glycine into uric acid indicates over-production of uric acid by de novo purine biosynthesis. This metabolic aberration, though considered to be inborn (3), may be modified by changing of life style, aging and long-term therapy. In the patient under study, the protracted use of allopurinol seems to have played the most important role. Aging contributed to a certain extent, and changing life style was the least significant factor.

Salvage of circulating hypoxanthine by tissues of the mouse

Hypoxanthine is an inefficient precursor of purine nucleotides in mouse tissues. In vitro, mouse erythrocytes salvage less than 10% of hypoxanthine (10 microM) added to whole blood in 30 min of incubation at 37 degrees C. In vivo, circulating hypoxanthine is rapidly degraded (greater than 90% in 10 min) to allantoin and uric acid. All tissues examined (other than erythrocytes) converted small amounts of hypoxanthine to nucleotides, with kidney and lung being the most active tissues examined. It is estimated that less than 2% of circulating hypoxanthine is salvaged in the mouse; the remainder is catabolized.

Activation of xanthine dehydrogenase during the prenatal period through L-thyroxine, thiourea and cycloheximide

Xanthine dehydrogenase activity in the liver of embryonic chicks has been shown to be inducible by L-thyroxine, thiourea, and cycloheximide. Results reported here indicate different mechanisms underlying the activation through L-thyroxine on the one hand, and through thiourea and cycloheximide on the other. Using hepatocyte suspension and homogenized liver, it has been shown that prenatal activation of xanthine dehydrogenase results in increased rate of uric acid formation from nucleic acids and purine derivatives, but not from amino acids.

Purine metabolism in high- and low-uric acid lines of chickens: hypoxanthine/guanine phosphoribosyltransferase activities

The activity of hypoxanthine/guanine phosphoribosyltransferase (HGPRT) was examined in the livers and kidneys of two genetic lines of chickens selected for different plasma uric acid levels. Previous work demonstrated that the high-uric acid line (HUA) had significantly greater de novo uric acid synthesis rates in kidney tissue compared to the low-uric acid line (LUA). In addition, phosphoribosylpyrophosphate (PRPP) synthetase and xanthine dehydrogenase activities in livers and kidneys were significantly higher in the HUA compared to the LUA line. PRPP pool sizes were also significantly higher in both livers and kidneys of HUA birds. HGPRT activities in livers of HUA birds were significantly (P less than 0.05) greater than in LUA birds. The mean value of liver HGPRT was 7.36 +/- 0.25 pmole inosine-5'-monophosphate (IMP) and 6.05 +/- 0.27 pmole IMP produced/micrograms protein/hr, respectively, for the HUA and LUA lines. There were no significant differences (P greater than 0.05) in kidney HGPRT activities between the two groups. The mean value of kidney HGPRT was 52.87 +/- 1.62 pmole IMP and 50.72 +/- 1.62 pmole IMP produced/micrograms protein/hr, respectively, for the HUA and LUA line. Elevated liver HGPRT may serve to enhance the regeneration of PRPP in the HUA liver. Elevated liver PRPP synthetase and PRPP pool size suggest an increased flux through the de novo purine biosynthetic pathway in HUA birds. The resulting additional pyrophosphate from the glutamine PRPP amidotransferase reaction would stimulate recovery of PRPP and spare the system from a substantial loss of energy.

Stimulation of uric acid production and depression of increase in plasma glutamine concentration by insulin in chickens infused with ammonia

1. A single intraportal injection of insulin remarkably stimulated uric acid production in the chicken infused with ammonium acetate and significantly depressed the increase in plasma glutamine concentration by the infusion of ammonia (P less than 0.01 at 20 min, P less than 0.05 at 40 min after the start of infusion). 2. The increases in ammonia concentration in the blood and kidney during the infusion of ammonia were not affected by the insulin pretreatment. 3. The depressive effect of insulin on the increase in plasma glutamine concentration by ammonia may be due to the acceleration by insulin of incorporation of glutamine into biosynthetic pathway of uric acid in the chicken.

Synthesis of 3-N-ribosyluric acid 5'-monophosphate by red cells of the bovine fetus

Although 3-N-ribosyluric acid (3-RUA) was not detected in the red cells of bovine fetuses, 3-N-ribosyluric acid 5'-monophosphate, the immediate precursor of 3-RUA, was synthesized from uric acid and 5-phosphoribosyl-1-pyrophosphate (PRPP) by hemolysates of fetal red cells. These preparations also synthesized 3-N-ribosylxanthine 5'-monophosphate from xanthine and PRPP. Partially purified extracts of fetal and adult erythrocytes of cattle had similar enzyme activity and the same specificity toward xanthine and orotic acid. Therefore, it was concluded that the absence of 3-RUA in fetal red cells was not a result of lack of the enzyme orotate phosphoribosyltransferase (EC 2.4.2.10).

Ethanol-induced hyperuricemia: evidence for increased urate production by activation of adenine nucleotide turnover

Consumption of alcoholic beverages is associated with hyperuricemia and gout. To determine the contributions to this process of increased production and decreased excretion of uric acid, we gave oral ethanol (1.8 g per kilogram of body weight every 24 hours) for eight days or intravenous ethanol (0.25 to 0.35 g per kilogram per hour) for two hours to six patients with gout. During the long-term oral study we observed the following: serum urate levels increased from 8.4 +/- 0.4 (mean +/- S.E.) to 10.1 +/- 0.9 mg per deciliter; whole blood lactate reached a peak of 3.1 +/- 0.7 mM from a base line of 1.3 +/- 0.3 mM; and urinary oxypurines increased to 641 +/- 397 per cent of the base-line value. Urate clearance increased to 145 +/- 25 per cent of the base-line value. Daily uric acid turnover increased from 1010 mg per deciliter to 170 +/- 17 per cent of the base-line value. During short-term intravenous ethanol administration, serum urate levels, urate clearance, and urinary uric acid excretion were not substantially altered from the base-line period. Urinary oxypurine levels increased to 341 to 415 per cent of base-line values. Urinary radioactivity, originating from the adenine nucleotide pool labeled by [8-(14)C]adenine, increased to 127 to 149 per cent of base-line values. These data indicate that ethanol increases urate synthesis by enhancing the turnover of adenine nucleotides.

Effects of azaserine treatment on plasma glutamine concentration and uric acid production in chickens fed low and high protein diets

Azaserine injected intravenously decreased uric acid in the blood and urine 1.6 and 2 times, respectively. It also resulted in 3 times larger increase in plasma glutamine concentration in chickens fed a 20% protein diet than in those fed a 5% protein diet, but it had no effect on liver glutamine synthetase activity in either dietary group. Thus the resultant concentration of plasma glutamine in the chickens fed the high protein diet was higher than in those fed the low protein diet, the reverse of the relationship observed before the injection. The infusion of ammonium acetate caused less of a rise in plasma glutamine concentration, but increased uric acid in the urine and blood, more with the high protein feeding than the low protein feeding. Pretreatment with azaserine further augmented the increase in plasma glutamine concentration caused by the infusion of ammonium acetate in the chickens fed the high protein diet but not in those fed the low protein diet, and concurrently removed the stimulatory effect of ammonia on uric acid in the blood and urine of both dietary groups. These data indicate that both glutamine in intact chickens and the increased glutamine in the ammonia-infused chickens are converted to uric acid more by high protein feeding than by low protein feeding, and this is a major reason for the low concentration of plasma glutamine in the chickens fed a high protein diet.

Influence of dietary purines on pool size, turnover, and excretion of uric acid during balance conditions. Isotope studies using 15N-uric acid

Pool size, turnover, and excretion of uric acid were investigated in three normal subjects both during purine-free, isoenergetic liquid formula diet and during additional purine administration by use of isotope dilution techniques. The fractional turnover of the uric acid pool was increased during dietary purine administration suggesting an increased total body uric acid clearance as a result of the increase in renal clearance. Fractional turnover increased more in the female subject than in males, while pool size was increased less. It can be calculated from the results obtained that endogenous uric acid synthesis is not inhibited by dietary purines.

Interrelationships between gluconeogenesis and uricogenesis in chicken liver

1. Experiments performed on isolated hepatocytes and perfused liver of starved chickens showed that gluconeogenesis from lactate, glycerol and fructose was inhibited by 22-100% on addition of urate precursors. 2. The inhibition was associated with an increased rate of urate formation. 3. 2,4-Dinitrophenol (40 microM), 2-bromooctanoate (2 mM) and 3-mercaptopicolinate (3MPA) (0.5 mM) were inhibitory with respect to gluconeogenesis but did not significantly affect the rate of urate formation. 4. The possible interrelationships between gluconeogenesis and uricogenesis are considered in terms of a competition for ATP and for other metabolites between the two pathways. 5. An interplay of both pathways at the level of anion transfer across the inner mitochondrial membrane is also discussed.

Adaptation of urate synthesis in chicken liver

1. Urate synthesis was measured in hepatocytes from chickens after starvation or high-protein feeding. Adaptation occurred only on the high-protein diet. 2. The theoretical balances of reactions from alanine (5 alanine + 3 O2 = urate + 1.5 glucose + glycine) and asparagine (3 asparagine + 2 O2 = urate + ammonia + 0.5 glucose + glycine) agree reasonably well with the experimental results. 3. Enzymes directly involved in urate synthesis from these amino acids increase up to 12-fold on the high-protein diet; only amidophosphoribosyltransferase activity appears to be rate-limiting for urate synthesis. 4. The processes of nitrogen disposal in chicken and rat are compared and discussed.

[Different effect of taurolithocholate and chenodeoxycholate on structure and function of isolated hepatocytes (author's transl)]

Alterations of cellular membranes under the influence of bile acids seem to be of pathophysiological importance in cholestasis. The effect of taurolithocholic acid (TLCA) and chenodeoxycholic acid (CDCA) on membrane structure and release of cellular enzymes was studied on isolated rat hepatocytes. The response of urea synthesis to glucagon was used as a parameter of membrane function. The threshold dose of TLCA, marked by rapidly increasing enzyme release, was about 100 micrometers, whereas that of CDCA was between 500 and 1,000 micrometers. Addition of albumin (1 g-%) increased the threshold dose of CDCA; this occurred for TLCA only 8 g-%. Electron-microscopical alterations of the endoplasmic reticulum and submembranous areas were found with concentrations below these threshold doses even in the presence of albumin. These alterations are interpreted as disturbance of cellular transport and energy metabolism. TLCA inhibited glucagon response of cells in concentrations below 100 micrometers. These results demonstrate an influence of the bile acids studied on structure and function of liver cell membranes, which may be of importance in the pathogenesis of cholestasis. The rough endoplasmic reticulum could be another cellular structure which is affected by these bile acids.

Catecholamine-induced hyperuricemia in eviscerated rats with functional hepatectomy

The presence of extra-hepatic systems for uric acid production and their role in catecholamine-induced hyperuricemia were studied in eviscerated rats with functional hepatectomy. In these animals, the plasma uric acid level progressively increased with a decrease of allantoin, and isoproterenol subcutaneously administered in low doses produced an evident hyperuricemia. The effect of isoproterenol was seen even in nephrectomized animals, but all effects were abolished by pretreatment with allopurinol. Epinephrine and norepinephrine also produced hyperuricemia, though to a lesser extent than isoproterenol. Propranolol inhibited the hyperuricemic effects of isoproterenol and epinephrine, while phentolamine potentiated the effects of epinephrine. Electrical stimulation of the splanchnic nerve also produced hyperuricemia in eviscerated rats with functional hepatectomy, and this state was abolished by pretreatment with propranolol and by adrenalectomy but was not affected by pretreatment with phentolamine. Thus, beta adrenoceptor agonists stimulate production of uric acid in tissues other than the liver and the viscera, and hyperuricemia results. An effect similar to that on the uric acid level was also observed for the levels of plasma lactate, creatinine and glutamic oxalacetic transaminase in rats given isoproterenol.

Purine metabolism studies in the high and low uric acid containing lines of chickens: de novo uric acid synthesis and xanthine dehydrogenase activities

De novo purine synthesis has been examined in two genetic lines of chickens selected for their plasma uric acid levels. Synthesis rates were determined using aqueous extracts of tissue acetone powders. The high uric acid line (HUA) had significantly greater kidney synthesis rates compared to the low uric acid (LUA) birds (P less than .05). The mean value of kidney de novo uric acid synthesis rates was 5.65 +/- .65 micrograms and 3.6 +/- .24 micrograms uric acid synthesized/mg acetone powder/hour, respectively, for the HUA and LUA birds. Kidney uric acid synthesis rates were significantly correlated to plasma uric acid levels (P = .07). No correlation was seen between liver de novo uric acid synthesis rates and plasma uric acid levels. Plasma uric acid levels were monitored in both lines from hatching through 42 weeks of age. In the HUA line peaks of uric acid level were noted during the 2nd, 4th, and 8th week followed by a fairly abrupt rise in levels after the 20th week, whereas in the LUA males a broad peak in the early weeks was followed by a gradual rise in levels after the 20th week. The LUA females had slightly elevated levels during the first weeks; however, no significant changes occurred after the 20th week. Xanthine dehydrogenase (XDH) activities in kidney acetone powders from the HUA line were significantly higher compared to those from the LUA line (P less than .05). The mean value of kidney XDH activity was 85.41 +/- 13.81 and 46.35 +/- 6.71 mmoles NAD reduced per milligram acetone powder per hour, respectively, for the HUA and LUA lines. There was no significant correlation between liver XDH activities and plasma uric acid levels; however, the activity was significantly higher in the HUA than in the LUA line.

Formation of hydrogen peroxide in normal and copper-treated rat endometrium

An intrauterine copper device stimulated endogenous hydrogen peroxide formation in whole homogenates and in the mitochondrial and microsomal (but not the nuclear) fractions of rat endometrial tissues. Uric acid also accumulated in the endometrium of copper-treated rats, but not in those fitted with a nylon device or sham operated. It is suggested that the contraceptive effect of copper may be related to these events.

Primary overproduction of urate caused by a partial deficiency of hypoxanthine-guanine phosphoribosyl transferase

Inherited enzyme deficiencies are found in a small proportion of patients with gout who produce an excess of uric acid. The clinical, biochemical and therapeutic aspects of a case of hyperuricaemia caused by an atypical mutant hypoxanthine-guanine phosphoribosyl transferase are presented. Urate overproduction was moderate and controlled by allopurinol therapy.

Quantification of renal uric acid synthesis in the rat

The excretion of nephrogenic uric acid in the urine of Sprague-Dawley rats was estimated by use of the isotope-dilution technique. In nonfasted rats the urine-to-plasma specific activity ratio (SAR) of [14C]uric acid was 0.93, suggesting that a minimum of 7% of the uric acid excreted in the urine is synthesized in the kidney. During hypoxanthine infusion the SAR decreased in a dose-related fashion, indicating that the rat kidney is capable of synthesizing relatively large amounts of uric acid and that circulating precursor levels may in part regulate the renal synthesis of uric acid. During allopurinol infusion the SAR increased to 1.0, demonstrating that the SAR is a valid indicator of the contribution of nephrogenic uric acid excreted into the urine. Results of perfusion studies in isolated rat kidneys suggest that uric acid is the major end product of purine catabolism in the rat kidney and that some uric acid formed in the kidney may be absorbed directly into the circulation.

Variant human phosphoribosylpyrophosphate synthetase altered in regulatory and catalytic functions

An inherited, structurally abnormal and superactive form of the enzyme 5-phosphoribosyl 1-pyrophosphate (PP-ribose-P) synthetase (EC 2.7.6.1) has been characterized in fibroblasts cultured from a 14-yr-old male (S.M.) with clinical manifestations of uric acid overproduction present since infancy. PP-ribose-P synthetase from the cells of this child showed four- to fivefold greater than normal resistance to purine nucleotide (ADP and GDP) feedback inhibition of enzyme activity and hyperbolic rather than sigmoidal inorganic phosphate (Pi) activation in incompletely dialyzed extracts. Excessive maximal velocity of the enzyme reaction catalyzed by the mutant enzyme was indicated by: enzyme activities twice those of normal at all concentrations of Pi in chromatographed fibroblast extracts; normal affinity constants for substrates and for the activator, Mg2+; and twofold greater than normal activity per immunoreactive enzyme molecule. The mutant enzyme thus possessed deficient regulatory and superactive catalytic properties, two mechanisms previously demonstrated individually to underlie the excessive PPRribose-P and uric acid synthesis of affected members of families with superactive PP-ribose-P synthetases. Increased PP-ribose-P concentration (4-fold) and generation (2.7-fold) and enhanced rates of PP-ribose-P dependent purine synthetic reactions, including purine synthesis de novo, in S.M. fibroblasts confirmed the functional significance of this patient's mutant enzyme. Diminished stability of the variant PP-ribose-P synthetase was manifested in vitro by increased thermal lability and in vivo by deficiency of enzyme activity at Pi concentrations greater than 0.3 mM in hemolysates and by an accelerated, age-related decrement in enzyme activity in lysates of erythrocytes separated by specific density. Despite the diminished amount of PP-ribose-P synthetase in the S.M. erythrocyte population, S.M. erythrocytes had increased PP-ribose-P concentration and increased rates of incorporation of [14C]adenine and hypoxanthine into acid-soluble nucleotides during incubation at 1 mM Pi. These findings provided further confirmation of the extent to which PP-ribose-P synthesis is modulated in the normal cell at physiological Pi concentration by purine nucleotide inhibition of PP-ribose-P synthetase. The activity and kinetic characteristics of PP-ribose-P synthetase from fibroblasts of the mother of patient S.M. indicated that this woman was a heterozygous carrier of the enzyme defect expressed in hemizygous manner by her son.

The role of biochemistry in drug research

The present and the future role of biochemistry in the search for a new therapeutic agent is reviewed. It is stated that the great importance of the various disciplines of biochemistry, including pathobiochemistry and pharmacological biochemistry, is presently recognized, and the involvement of biochemistry in drug research is increasing. Biochemistry at the present time and in the future will utilize the already known basic biological principles for the new development of new and more useful medicines. It is emphasized that the limiting factor in new drug discovery today, however, is the lack of new basic discoveries in biology.

On the pathogenesis of stone formation in stone-eliminating patients

The clinical peculiarities, and the etiological and pathogenetic factors of urolithiasis in 296 patients suffering from spontaneous stone elimination were studied. It was established that 209 patients eliminated stones consisting of uric acid, sodium salts and ammonium salts. Moderate hypocalcemia and hyperphosphatemia and also hyperuricemia and hyperuricuria were present. There were 39 'eliminators' of calcium stones. Their blood calcium content was higher, hypercalciuria, inorganic phosphorus and normal uric acid, were noted. Compound stones were present in 48 observations. When carrying out additional biochemical tests in 57 patients with calcium and compound stones, primary hyperparathyroidism was diagnosed in 34 observations; and parathyroidectomy was successfully performed.

Rate-limiting factors in urate synthesis and gluconeogenesis in avian liver

1. Urate synthesis and other metabolic characteristics of isolated chicken hepatocytes were studied. 2. The distinction is made between immediate precursors of the purine ring (glycine, glutamine, aspartate, formyltetrahydrofolate, bicarbonate) and ultimate precursors from which the immediate precursors are formed in the liver. 3. In hepatocytes from well-fed chickens the rate of urate synthesis was not greatly increased by the addition of amino acids or NH(4)Cl, but in hepatocytes from 72h-starved chickens the rate was much increased when alanine or asparagine was added as the only substrate. Other amino acids, when added alone, did not affect the rate. The exceptional effect of alanine and asparagine is due to the ready formation of the immediate precursors. 4. Conditions are described under which glutamine, serine, glycine plus formate, ribose and glucose increased the rate of urate synthesis. 5. At 1mm-NH(4)Cl (a concentration not much higher than that of blood plasma) the rate of urate synthesis in the presence of lactate was increased, but higher concentrations inhibited urate synthesis in the presence of lactate or alanine; with alanine even 1mm-NH(4)Cl was inhibitory. 6. Glucose synthesis from lactate, alanine or dihydroxyacetone was also inhibited by 1mm-NH(4)Cl. 7. NH(4)Cl inhibition of urate and glucose synthesis was paralleled by an increased rate of glutamine synthesis. Thus in the presence of NH(4)Cl the gluconeogenic precursors are diverted from the pathway of gluconeogenesis to that of glutamate and glutamine synthesis. This implies that the synthesis of these amino acids is the primary process in the detoxication of ammonia in the avian liver. 8. Urate synthesis, like urea synthesis, can be looked on as a cyclic process with either phosphoribosyl pyrophosphate or ribose acting as the carrier on which the purine ring is assembled. 9. The energy requirements of urate synthesis depend on whether phosphoribosyl pyrophosphate is regenerated from IMP by pyrophosphorylase or by phosphorylation and pyrophosphorylation of ribose. It is 6 or 9 pyrophosphate bonds of ATP respectively.

Protein intake, hepatic purine enzyme levels and uric acid production in growing chicks

Changes in hepatic purine enzyme activities of chicks fed diets containing 11%, 20%, 43% and 80% protein were correlated with protein intake and uric acid production in order to identify those enzymes with activities that parallel closely and may regulate uric acid production. Nucleoside phosphorylase, xanthine dehydrogenase, adenylosuccinate synthetase and adenosine kinase correlated positively with protein intake and uric acid production. Adenosine deaminase, 5'-nucleotidase (AMP), adenylate deaminase and adenine phosphoribosyltransferase correlated negatively with protein intake and uric acid production. Hypoxanthine phosphoribosyltransferase and 5'-nucleotidase (IMP) were unaffected by protein intake and did not correlate with uric acid production. The ratio of adenosine kinase to adenosine deaminase correlated positively with protein intake and uric acid production. The increased activities of adenylosuccinate synthetase and adenosine kinase, along with the reduced activities of 5'-nucleotidase and adenylate deaminase, in liver from chickens fed the 80% compared with the 11% protein diet demonstrate enhanced synthesis of adenine nucleotides. Since adenine nucleotides are essential cofactors for de novo purine synthesis, it is proposed that adenylosuccinate synthetase, adenosine kinase, 5'-nucleotidase and adenylate deaminase are key enzymes involved in the regulation of purine biosynthesis.