Hiroyuki Ohata

Effect of ethanol and fructose on plasma uridine and purine bases

To determine whether both ethanol and fructose increase the plasma concentration of uridine, we administered ethanol (0.6 g/kg) or fructose (1.0 g/kg) to seven normal subjects. Both ethanol and fructose increased the plasma concentration of uridine together with an increase in the plasma concentration of oxypurines, whereas fructose also increased the plasma concentration of uric acid, but ethanol did not. In ethanol ingestion and fructose infusion, an increase in the plasma concentration of purine bases correlated with that of uridine. These results strongly suggest that an increase in the plasma concentration of uridine is ascribable to increased pyrimidine degradation following purine degradation increased by ethanol and fructose.

Effect of amino acids on the plasma concentration and urinary excretion of uric acid and uridine.

To determine the effect of amino acids on the plasma level and urinary excretion of uric acid and uridine, 200 mL 12% amino acid solution, and 2 weeks later, 100 mL physiological saline solution containing glucagon (1.2 microg/kg weight), was infused into five healthy men. Both increased the urinary excretion of uric acid and the concentration of glucagon, insulin, and glucose in plasma and pyruvic acid in blood, whereas they decreased the concentration of uridine and inorganic phosphate in plasma. However, neither the amino acid infusion nor glucagon infusion affected the concentration of purine bases (hypoxanthine, xanthine, and uric acid), cyclic adenosine monophosphate (cAMP) in plasma, or lactic acid in blood or the urinary excretion of oxypurines (hypoxanthine and xanthine), uridine, or sodium. These results suggest that glucagon may have an important role in the amino acid-induced increase in urinary excretion of uric acid and decrease in plasma uridine.

Effect of glucagon on the xylitol-induced increase in the plasma concentration and urinary excretion of purine bases.

To investigate whether glucagon affects the xylitol-induced increase in the production of purine bases (hypoxanthine, xanthine, and uric acid), the present study was performed with five healthy subjects. Intravenous administration of 300 mL 10% xylitol increased the plasma concentration and urinary excretion of purine bases, erythrocyte concentrations of adenosine monophosphate (AMP) and adenosine diphosphate (ADP), and blood concentrations of glyceraldehyde-3-phosphate (GA3P) + dihydroxyacetone phosphate (DHAP), fructose-1,6-bisphosphate (FBP), and lactic acid; it decreased the blood concentration of pyruvic acid and the plasma concentration and urinary excretion of inorganic phosphate. However, intravenous administration of 1 mg glucagon together with xylitol reduced the xylitol-induced changes in oxypurines, pyruvic acid, GABP + DHAP, and FBP, whereas it promoted the xylitol-induced increase in the urinary excretion of total purine bases and did not affect the xylitol-induced increase in the plasma concentration of total purine bases. In addition, in vitro study demonstrated that sodium pyruvate prevented the xylitol-induced degradation of adenine nucleotides in erythrocytes. These results suggested that gluconeogenesis due to glucagon increased the production of pyruvic acid, accelerated the conversion of NADH to NAD, and thereby prevented both the xylitol-induced degradation of adenine nucleotides in organs similar to erythrocytes and the inhibition of xanthine dehydrogenase in the liver and small intestine, resulting in decreases in the plasma concentration and urinary excretion of oxypurines. However, it was also suggested that in the liver storing glycogen, glucagon-induced glycogenolysis accumulated sugar phosphates, resulting in purine degradation, since the xylitol-induced increase in the NADH/NAD ratio partially blocked glycolysis at the level of GABP dehydrogenase. Therefore, administration of glucagon together with xylitol may synergistically increase purine degradation more than xylitol alone, despite decreases in the plasma concentration and urinary excretion of oxypurines.

Effect of bucladesine sodium on the plasma concentrations and urinary excretion of purine bases and uridine

To examine whether bucladesine sodium affects the plasma concentrations of purine bases (hypoxanthine, xanthine, and uric acid) and uridine, 100 mL of physiological saline containing bucladesine sodium (6 mg/kg weight) was administered intravenously to eight healthy subjects for 1 hour after overnight fast except for water. Blood was drawn 30 minutes before, and 30 minutes and 1 hour after the beginning of the infusion, and 1-hour urine was collected before and after the beginning of the infusion. Two weeks later, 100 mL of only physiological saline was administered under the same protocol. Bucladesine sodium decreased the plasma concentrations of hypoxanthine by 36% and by 37%, and of xanthine by 16% and 33%, and of uridine by 17% and 30%, 30 minutes and 1 hour after the beginning of the infusion, respectively, and increased the urinary excretion of hypoxanthine and uric acid by 140% and 30%, respectively, after the beginning of the infusion. However, it did not affect the plasma concentration of uric acid or the urinary excretion of xanthine, and the urinary excretion of uridine was less than 0.2 micromol/h before or after bucladesine sodium infusion. On the other hand, physiological saline alone did not affect any of the values described. These results suggest that bucladesine sodium acts on the secretory process of the renal transport of hypoxanthine, resulting in the increased urinary excretion of hypoxanthine, and further suggest that bucladesine sodium enhances the uptake of uridine in plasma to liver cells.

Effect of glucagon on the plasma concentration of uridine

To determine whether glucagon affects the plasma concentration of uridine, we administered 100 mL physiological saline containing 1 mg glucagon or 100 mL physiological saline alone intravenously over 1 hour to healthy subjects. Glucagon decreased the plasma concentration of uridine from 5.72 +/- 1.05 to 4.80 +/- 0.60 micromol/L but increased the concentrations of cyclic adenosine monophosphate (cAMP) in plasma and pyruvic acid and lactic acid in blood 59-, 1.4-, and 1.3-fold, respectively. Although glucagon increased urinary excretion of uric acid, it did not affect the plasma concentration of purine bases (hypoxanthine, xanthine, and uric acid) or urinary excretion of oxypurines and uridine, indicating that glucagon does not affect purine degradation and suggesting that glucagon does not affect adenosine triphosphate (ATP) consumption-induced pyrimidine degradation. In contrast, physiological saline did not affect any of the measured variables. These results suggest that glucagon enhanced Na+-dependent uridine uptake from the blood into the cells, since glucagon stimulates Na+-dependent uridine uptake into cells in vitro.

'Pseudohypouricosuria' in alcaptonuria: homogentisic acid interference in the measurement of urinary uric acid with the uricase-peroxidase reaction.

Urinary excretion of uric acid was found to be extremely low in a 58-year-old female patient with alcaptonuria. This was due to interference with the uricase-peroxidase method used, because analysis using high-performance liquid chromatography (HPLC) showed a normal urinary concentration of uric acid. In vitro experiments demonstrated that a high concentration of homogentisic acid in the patients urine inhibited the peroxidase reaction, possibly due to inhibition of the colour development of 3-methyl-N-ethyl-N-(β-hydroxyethyl)aniline (MEHA) and 4-aminoantipyrine, via the peroxidase reaction. A homogentisic acid concentration equivalent to that in plasma did not affect the uricase-peroxidase reaction. This result suggests that any assay based on a peroxidase method is affected by a high urinary concentration of homogentisic acid in patients with alcaptonuria.