Communications to the editor: Excretion of 4-formylaminoantipyrine as a new metabolite of aminopyrine in experimental animals

A new aspect of tolbutamide metabolism in the rabbit: the role of 1-butyl-3-(p-formylphenyl)sulphonylurea

We investigated the metabolism of tolbutamide by using synthetic 1-butyl-3-(p-formylphenyl)sulphonylurea (ATB), an intermediate in the metabolic pathway of tolbutamide. ATB (40 mg kg-1) administered intravenously to rabbits was oxidized to 1-butyl-3-(p-carboxyphenyl)sulphonylurea (CTB) and also reduced to 1-butyl-3-(p-hydroxymethylphenyl)sulphonylurea (HMTB). Therefore, it is likely that in the metabolism of tolbutamide, the oxidation of HMTB to ATB involved the reverse reaction, suggesting the reduction of ATB to HMTB. The oxidation of ATB to CTB was inhibited by disulfiram pretreatment. ATB was detected in the blood following intravenous administration of HMTB in rabbits pretreated with disulfiram. These results, confirm that ATB is an intermediate in the oxidative metabolism of tolbutamide in the rabbit.

Effects of experimental diabetes on aminopyrine metabolism in rats

1. The metabolism of aminopyrine has been investigated in normal, alloxan- and streptozotocin (STZ)-diabetic rats. The drug was administered i.p. and the serum concentrations of the unchanged aminopyrine and its main metabolites were measured using h.p.l.c. 2. Aminopyrine was metabolized at a slower rate in both diabetic rats, as judged from higher serum levels of the unchanged drug. Pharmacokinetic studies of aminopyrine in diabetic rats also showed a decrease in serum clearance of the drug and an increase in its serum half-life. 3. The serum concentrations of the metabolites 4-monomethylaminoantipyrine, 4-acetylaminoantipyrine and 4-formylaminoantipyrine decreased in diabetic rats. In contrast, serum levels of 3-hydroxymethyl-2-methyl-4-dimethylamino-1-phenyl-3-pyrazolin-5-on e increased over control values. Serum concentrations of 4-aminoantipyrine remained unaltered by the induction of diabetes. 4. The magnitudes of changes in serum levels of these metabolites were larger in alloxan-diabetes than in STZ-diabetes. 5. Additional support for changed metabolism of aminopyrine was obtained from the investigation of microsomal preparations from diabetic and normal rats. 6. These findings indicate that it is important to use intact animals for evaluation of the metabolism of drugs in pathological states.

Histological studies into rat liver following long-term application of aminophenazone, phenazone, and propyphenazone

Morphological studies by means of light microscopy are important for toxicological drug testing. More complete information on potential damage can be obtained only by combination of pharmacological, biochemical, hepatofunctional, and morphological tests and studies. No systematic tests had been applied to rats, in the past. Therefore, aminophenazone, phenazone, and propyphenazone were tested for periods up to 16 weeks. Long-term application of the three pyrazolone derivatives resulted in the following dose-dependent and time-dependent alterations: hepatocyte enlargement, fatty degeneration and reactive-inflammatory changes along with single-cell necrosis, round cellular infiltration of periportal fields, and Kupffer cell activation. The alterations differed in intensity by the following order: aminophenazone greater than phenazone greater than propyphenazone.

Simultaneous determination of aminopyrine hydroxylation and aminopyrine N-demethylation in liver microsomes by high-performance liquid chromatography

Aminopyrine and its metabolites, including 3-hydroxymethyl-2-methyl-4-dimethylamino-1-phenyl-3-pyrazoline-5-one which is a hydroxylated metabolite of aminopyrine, were separated on a reversed-phase (C8) Radial-Pak column using a mobile phase of methanol-triethylamine-water (30:1:69) adjusted to pH 5.40 with acetic acid. Detection of the peak was performed by an ultraviolet detector at 254 nm. By the rapid and simple method, aminopyrine hydroxylation as well as aminopyrine N-demethylation in liver microsomes can be examined simultaneously.

Irreversible binding of 3-14C-antipyrine to hepatic protein in vivo and in metabolizing liver microsomes

After i.p. injection of 3-14C-antipyrine (10 micronmole = 1.9 mg with 10 micronCi per 10 g of body weight) to mice radioactivity was irreversibly bound to liver proteins. The irreversible binding reached maximal values of 0.15 nmole/mg protein in liver microsomes after 30-60 min. During 60 min incubation with liver microsomes of mice and rabbits (phenobarbital pretreated) and a NAKPH-regenerating system 3-14C-antipyrine was irreversibly bound to microsomal protein at a rate of 1.5 nmole/mg protein (mouse) and 3 nmole/mg protein (rabbit). In identical incubates with rabbit liver microsomes the 4-hydroxylation of antipyrine was 24 nmole/mg protein in 60 min and formaldehyde production from antipyrine 3 nmole/mg protein in 60 min. In incubates with rabbit liver microsomes the binding rate was 80-90% inhibited by 1mM metyrapone, SKF 525-A and trichloropropene epoxide respectively; 4-hydroxylation was 70-80% inhibited by the same substances. In the presence of 1mM GSH, cysteine or ethylene diamine binding was 30-40% inhibited, whereas 4-hydroxylation showed no inhibition.