Hypoxanthine as a measurement of hypoxia

The hypoxanthine concentration in plasma was found to be a sensitive parameter of hypoxia of the fetus and the newborn infant. The plasma level of hypoxanthine in the umbilical cord in 29 newborn infants with normal delivery varied between 0 and 11.0 mumol/liter with a mean of 5.8 mumol/liter, SD 3.0 mumol/liter. Compared with this reference group the hypoxanthine concentration in plasma of the umbilical cord in 10 newborn infants with clinical signs of intrauterine hypoxia during labor was found to be significantly higher, with a range of 11.0-61.5 mumol/liter, with a mean of 25.0 mumol/liter, SD 18.0 mumol/liter. The plasma level of hypoxanthine in two premature babies developing an idiopathic respiratory distress syndrome was monitored. The metabolite was found to be considerably increased, in one of them more than 24 hr after a period of hypoxia necessitating artificial ventilation. The hypoxanthine level in plasma of umbilical arterial blood was followed about 2 hr postpartum in three newborn infants with clinical signs of intrauterine hypoxia. The decrease of the plasma concentration of the metabolite seemed to be with a constant velocity, as it was about 10 mumol/liter/hr in these cases. A new method was used for the determination of hypoxanthine in plasma, based on the principle that PO2 decreased when hypoxanthine is oxidized to uric acid.

Effects of drugs on uric acid in man

In this review the drugs capable of increasing or lowering the serum urate concentration are considered with regard to mechanism of action and significance of the effect, where known. Several hypouricemic agents, probenecid, sulfinpyrazone, and allopurinol, are considered in further detail because of their major clinical importance. No effort has been made, however, to summarize the relative clinical indications for each agent. In addition, in those cases where specific details could not be included because of limitation of space, the appropiate reference has been given.

Synthesis of uric acid in isolated normothermic perfused mongrel and Dalmatian dog kidneys

Renal synthesis of uric acid (urate) in the dog was demonstrated by use of two isolated kidney preparations during pulsatile perfusion at 37 degrees C with artificial perfusate or with a plasma fraction. During perfusion of mongrel and Dalmatian dog kidneys with 0.5 mg of [14C]xanthine per 100 ml, a mean of 24.3 and 25.4 mug of [14C]urate per minute, respectively, entered either urine or perfusate after its synthesis in the isolated kidney. Approximately 6.2% of the combined extracellular radiolabeled urate formed in the isolated mongrel kidney was excreted in the urine and 15.7% in the urine of isolated Dalmatian dog kidneys. Recirculating the perfusate without the kidney did not convert any radioactively labeled xanthine to urate and therefore the radioactively labeled urate appearing in the urine and recycled perfusate must have been formed in the renal parenchyma. Renal synthesis of urate was blocked by the xanthine oxidase inhibitor allopurinol. In the presence of allopurinol, [14C]xanthine was excreted unchanged into the urine.

Renal urate excretion in animal models

Several aspects of the comparative physiology and pharmacology of renal urate handling are considered; with special attention to bidirectional transport, the existence of intrarenal urate synthesis and degradation in certain species, and the nature and sites of the reabsorptive and secretory processes. Interspecies variations in the sensitivity of the kidney to uricosuric agents and the degree of specificity of the secretory mechanism are discussed. A variety of techniques, especially as applied in certain nonhuman primates, have led to a concept of very rapid trans-tubular fluxes of urate--a concept which may apply in man.

Ammonia and uric acid formation after rapid intravenous fructose administration to healthy subjects and patients with compensated cirrhosis of the liver

To seven healthy volunteers, 12 and 24 g i.v. fructose were administered in the form of 20% solution at a rate of 4 g/min. After both doses, during the 10th min after the completed intravenous administration, a statistically significant increase of serum ammonia and serum uric acid occurred. After 24 g, the rise of the uric acid level remains significant during the 40th min after administration, while ammonia values return to the basal level. Increments of ammonia and uric acid are higher after a larger fructose dose. Under the same set-up and at the same rate, 24 g fructose were administered to eight patients with compensated cirrhosis of the liver. The rise of uric acid was practically the same as in healthy subjects similar to the rise of the ammonia level during the 10th min after administration. 40 min after administration, however, the ammonia level in cirrhotic patients remained significantly raised, as compared with the initial level.

Pharmacologic approach to the maintenance of urate homeostasis

A reduction in the serum urate concentration in hyperuricemic subjects can be achieved by increasing the renal excretion of uric acid, by inhibiting its synthesis, or by a combination of both modalities. The three most commonly used hypouricemic drugs are probenecid, sulfinpyrazone and allopurinol. Each drug has been considered in detail with regard to its mechanism of action, metabolism, diverse metabolic effects, side effects and interaction with other drugs. In addition, guidelines for the use of these drugs in hyperuricemic subjects are proposed.

Urate synthesis in the perfused chick liver

Urate synthesis was studied in a perfused chicken liver preparation. The perfused liver had an ATP/ADP ratio of 0.29+/-0.05(6) compared with 0.34+/-0.07(10) in liver obtained from chicks under ether anaesthesia. Lactate/pyruvate ratios were 9.4+/-1.7(5) in the perfused liver and 14.8+/-1.8(5) in the rapidly sampled liver. Urate synthesis was only marginally stimulated by glycine, glutamine, aspartic acid or NH(4)Cl, but significant increases were observed with phosphoribosyl pyrophosphate, aminoimidazolecarboxylic acid riboside, inosine, inosinic acid and xanthine. Urate synthesis from glycine, glutamine, NH(4)Cl, asparagine, alanine, histidine and a mixture of 21 amino acids was obtained on inclusion of insulin in the perfusion medium. Evidence for the inclusion of the carbon of histidine into uric acid was obtained. Aspects of the energy consumption associated with the conversion of excess of amino acid into uric acid are considered.