A high performance liquid chromatographic assay for AMP-deaminase activity in the erythrocytes of healthy subjects and patients with inherited purine disorders.

A novel method for measuring AMP-deaminase activity in human erythrocytes is presented, based on the determination of the reaction product, IMP, using high performance liquid chromatography. IMP formation was found to be proportional both to the incubation time and the amount of haemolysate over a wide range. The minimal detectable AMP-deaminase activity was more than 1000 times lower than the mean activity found in healthy controls (1083 nmol/h/mg Hb). No marked difference of activity was found in the patients with the following inherited purine disorders: familial juvenile gouty nephropathy and deficiencies of adenosine deaminase, hypoxanthine-guanine phosphoribosyltransferase or adenine phosphoribosyltransferase. The activity in the erythrocytes of patients with chronic renal failure was also similar to controls. The existence of subjects with low erythrocyte AMP-deaminase activity in the population has been confirmed.

Pharmacokinetic and pharmacodynamic studies of glibenclamide in non-insulin dependent diabetes mellitus.

1. The pharmacokinetic and pharmacodynamic properties of oral glibenclamide have been studied in 31 hospitalised in-patients and 79 ambulant out-patients with diabetes mellitus. 2. Breakfast was found to have no significant influence on the kinetic behaviour of glibenclamide or on the effect of this drug on blood glucose utilisation. 3. The time course of glibenclamide kinetics after 20 mg dosing was adequately described by a two-compartment open model, yielding mean half-lives of 3.3 +/- 1.5 h (t1/2, lambda 1) and 9.7 +/- 1.2 (t1/2, z) for the initial and terminal elimination phases respectively. 4. No significant accumulation or change in kinetic profile occurred in patients who had normal renal and hepatic function, were treated continuously with glibenclamide, and then rechallenged after 8-12 weeks. 5. Despite inter-individual variations in drug absorption, peak plasma concentrations (Cmax) and the area under the plasma concentration-time curve (AUC(0-24] were dose-dependent over the dose range 5-20 mg. No significant dose-response behaviour was observed in respect of glucose utilisation, suggesting that there is little clinical benefit in using doses of glibenclamide above 5 mg day-1. 6. Comparison of plasma glibenclamide concentrations at different time-bands following doses of 5 and 10 mg showed a wider range in ambulant out-patients than in age-, sex-matched in-patients treated with the same dosages of drug. Mean plasma drug concentrations attained at all time bands up to 8 h after dosing were higher in out-patients than in in-patients, suggesting a tendency to 'over-compliance' by patients in anticipation of attendance at clinic.

Beer drinking and its effect on uric acid.

This study attempted to simulate the drinking habits of gout patients. Beer or squash was drunk over a 4-hour period on two successive days by five gouty and five normouricaemic men. Serum lactate increased with beer and squash, but elevation of plasma uric acid was confined to beer drinking. Urate clearance increased with both beverages, but 24-hour uric acid excretion was accentuated only by beer. The purine content of several beers was measured and the principal constituent found to be guanosine, which is probably the most readily absorbed dietary purine. It was concluded that the hyperuricaemic effect of beer was mediated by the digestion of purines contained by the beer and by an effect of ethanol on uric acid synthesis. There was no evidence that beer taken in usual quantities reduced the renal excretion of uric acid.

Azapropazone--a treatment for hyperuricaemia and gout?

In a metabolic ward study of five patients, azapropazone lowered plasma uric acid but exerted only a modest and variable uricosuric effect without altering urinary xanthine and hypoxanthine levels. An alternative mechanism other than uricosuria or xanthine oxidase inhibition must account for some of the hypouricaemic action of this drug. During the first day of treatment urine volume and pH declined sharply. In a separate investigation, 22 patients were given azapropazone and 18 were given allopurinol combined with colchicine for 3 months. Allopurinol reduced plasma uric acid more quickly but at the end of the study there was little difference in the hypouricaemic results achieved by both drugs. Recurrent gout occurred more frequently with allopurinol but side-effects were confined to those taking azapropazone. A slight rise in blood urea and creatinine and a fall in haemoglobin were also features of long-term azapropazone treatment.

A controlled study of diet in patients with gout.

To determine whether patients with gout have a diet which is distinctive in quality or quantity a careful dietary questionnaire was posed over 7 days to 61 men with gout and 52 control subjects. The average daily intake of most nutrients, including total purine nitrogen, was similar except that the patients with gout drank significantly more alcohol. Beer was the most popular beverage, and 25 (41%) of those with gout consumed more than 60 g alcohol daily (equivalent to 2 . 5 litres of beer). The heavy drinkers had a significantly higher intake of purine nitrogen, half of which was derived from beer. Though the effect of ingested purine on the blood uric acid is difficult to estimate, it probably was sufficient to have a clinical effect, augmenting the hyperuricaemic effect of alcohol itself.

Methylthioadenosine phosphorylase activity in human erythrocytes.

An enzyme capable of degrading 5'-methylthioadenosine to adenine was found in the human erythrocyte. A rapid assay for this enzyme, 5'-methylthioadenosine phosphorylase, was developed using high pressure liquid chromatography. The specific activity in 24 normal subjects was 8.9 +/- 2.0 nmol . mg-1 Hb . h-1. Levels within this range were also found in erythrocyte lysates from gouty subjects and patients with a variety of inborn errors of purine metabolism, including patients with a complete deficiency of the adenine salvage enzyme--adenine phosphoribosyltransferase. Erythrocyte lysates from the latter however, were unable to convert the adenine produced to AMP in a linked assay system, in contrast to controls and other patients. These results support the suggestion that adenine, which is excreted in quantity by patients with adenine phosphoribosyltransferase deficiency is derived endogenously from 5'-methylthioadenosine as a by-product of polyamine biosynthesis.