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PubMed1983

Effect of ethanol and metabolic substrates on the oxidation of aminopyrine, formaldehyde and formate by isolated hepatocytes.

The production of [14C]O2 from 14C-labeled aminopyrine involves the following sequence: Aminopyrine 1 leads to formaldehyde 2 leads to formate 3 leads to CO2 Ethanol has the potential to affect any of the above steps in this sequence. In isolated hepatocytes from fasted rats ethanol inhibited CO2 production from aminopyrine, but not from formaldehyde or formate. Significant inhibition was found at low levels of ethanol that do not affect aminopyrine metabolism by isolated microsomes. There was only a slight accumulation of formaldehyde and formate during the oxidation of aminopyrine to CO2, both in the absence or presence of ethanol. This suggests that step I is the rate-limiting step and the step most sensitive to ethanol. There was accumulation of formate during the oxidation of formaldehyde to CO2. Ethanol decreased this formate accumulation suggesting some inhibition of the overall rate of formaldehyde oxidation. Addition of pyruvate, lactate, fructose, xylitol and sorbitol increased the rate of CO2 production from aminopyrine, but not from formaldehyde or formate. This increase by the substrates is probably due to an increase in the availability of NADPH required for step I. There was a slight increase in the accumulation of formaldehyde or formate during the oxidation of aminopyrine to CO2 in the presence of the substrates. Pyruvate and fructose nearly completely prevented the inhibition of CO2 production from aminopyrine by ethanol. Partial prevention was noted with the other substrates. Reduction of the cellular redox state as a consequence of ethanol metabolism may interfere with the transport of NADPH out of the mitochondria and, consequently, decrease the availability of NADPH for step I.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminopyrine↗
PubMed1998

Updating prognosis of cirrhosis by Cox's regression model using Child-Pugh score and aminopyrine breath test as time-dependent covariates.

BACKGROUND AND AIMS: The determination of aminopyrine breath test on entry into the study was recently shown to improve the accuracy of prediction of death based on the Child-Pugh classification, but the possible usefulness of serial determinations of both parameters has not been assessed. In the present study, we aimed at evaluating whether serial determinations of aminopyrine breath test and Child-Pugh score improve prognostic accuracy in patients with cirrhosis, compared with determinations obtained only on admission. PATIENTS: In 74 patients with liver cirrhosis aminopyrine breath test and Child-Pugh score were obtained upon entry into the study. Patients were followed with sequential aminopyrine breath tests and assessments of the Child-Pugh score every 4-6 months. A total number of 232 determinations were obtained. During follow-up 45 patients died, on average after 12 months of follow-up. RESULTS: Child-Pugh score improved in the beginning of follow-up, and then remained fairly constant; aminopyrine breath test showed no improvement in the beginning of follow-up, but rather a slowly progressive decline. In patients who died, both the Child-Pugh score and the metabolism of aminopyrine were significantly more impaired in the last year preceding death (p < 0.05). Applying Cox's regression model with time-dependent covariates, Child-Pugh score and aminopyrine breath test were independent significant predictors of survival. The model with time-dependent covariates explained the observed survival much better than the model with time-fixed covariates (chi-sq. explained by regression = 31.45 vs 11.97; d.f. = 2; p = 0.0000001 vs 0.003). CONCLUSIONS: These data suggest that serial determinations of Child-Pugh score and aminopyrine breath test can be used to efficiently update prognosis of cirrhosis.

Aminopyrine↗
PubMed1988

Effect of aging on hepatic elimination of cimetidine and subsequent interaction of aging and cimetidine on aminopyrine metabolism.

Aging and cimetidine may each impair hepatic microsomal drug metabolism. To test if and by what mechanisms advanced age may increase sensitivity to the inhibitory effects of cimetidine, the interaction of these two factors with aminopyrine metabolism in the rat was studied using a correlative approach. Initial studies using the aminopyrine breath test indicated that a 40 mg/kg dose of cimetidine, i.p., impaired the 14CO2 exhaled by up to 76% more in aged (26-month) than in young (3- to 4-month-old) rats. Using an isolated liver perfusion to dissect out hepatic components of this phenomenon, it was found that various doses of cimetidine impaired aminopyrine clearance to a greater degree (P less than 0.05) in aged than in young livers. However, cimetidine metabolism in this system ranged from 36 to 78% less in aged versus young livers (P less than 0.05). Subsequent in vitro studies indicated that microsomes isolated from aged livers also averaged a 76% lower rate of cimetidine metabolism (P less than 0.05). A fixed cimetidine concentration, however, inhibited aminopyrine demethylation to the same degree in aged versus young rats (P less than 0.05). In vivo pharmacokinetics showed an age-related decrease in both aminopyrine and cimetidine systemic clearance. In the young rat the liver contributed about 30% to total systemic clearance of cimetidine. In the aged rat, all clearance was renal. Despite a decrease in glomerular filtration rate, net tubular cimetidine secretion was well-maintained. Despite this, absence of the hepatic component resulted in decreased overall systemic clearance of the drug in aged rats. It is concluded that (1) the aged rat liver exhibits impaired cimetidine metabolism, resulting in decreased overall systemic clearance of the drug despite normal net renal tubular secretion, (2) there is no age-related enhanced sensitivity to cimetidine of the hepatic microsomal oxidizing system using aminopyrine as the probe drug, and (3) the larger inhibition of aminopyrine metabolism in aged rats following various doses of cimetidine is due to decreased overall cimetidine clearance, resulting in higher concentrations of the inhibitor in the liver of aged rats.

Aging↗
PubMed1998

N-dealkylation of aminopyrine catalyzed by soybean lipoxygenase in the presence of hydrogen peroxide.

A hypothesis that lipoxygenase may mediate N-dealkylation of xenobiotics was investigated using the prototype drug aminopyrine and soybean lipoxygenase as a model enzyme in the presence of hydrogen peroxide. Formaldehyde production as a result of N-demethylation of aminopyrine exhibited pH optimum of 6.5. The reaction was dependent on the incubation time, amount of enzyme, and concentration of aminopyrine and hydrogen peroxide. Under the experimental conditions employed, the specific activity for N-demethylation of aminopyrine was found to be 823 +/- 93 nmoles per min/mg protein or 89 +/- 10 nmoles per min/nmole of enzyme. The reaction was significantly inhibited by nordihydroguaiaretic acid and gossypol, the classical inhibitors of lipoxygenase. Spectrophotometric analyses indicated the generation of a nitrogen-centered free-radical cation as the initial oxidation product of aminopyrine. The rate of accumulation of this radical species was also dependent on pH, the amount of enzyme, and concentration of aminopyrine and hydrogen peroxide. The radical production was markedly suppressed by ascorbate, glutathione, and dithiothreitol in a concentration-dependent manner. Preliminary data gathered for the oxidation of other chemicals indicated that the lipoxygenase exhibits a unique substrate specificity. Collectively, the evidence presented suggests for the first time that lipoxygenase pathway may be involved in N-demethylation of aminopyrine and other chemicals.

Aminopyrine↗
PubMed1978

Diurnal rhythms of aminopyrine metabolism: failure to sleep deprivation to affect them.

After a single oral dose of aminopyrine (9 mg/kg), mean salivary aminopyrine half-lives (t 1/2s) and metabolic clearance rates in 12 normal male volunteers exhibited diurnal variations. Salivary aminopyrine t 1/2s were approximately 50% longer at 8 P.M. (2.1 +/- 0.7 hr) than at 8 A.M. (1.4 +/- 0.3 hr). Mean aminopyrine metabolic clearance rates decreased 20% from 8 A.M. (418.2 +/- 152.0 ml/min) to 8 P.M. (335.3 +/- 107.6 ml/min). There were large interindividual variations in the magnitude of these diurnal changes in aminopyrine t 1/2 and metabolic clearance rates. There were nonsignificant changes in mean aminopyrine apparent volumes of distribution (aVd) which increased only slightly from 53.1 +/- 20.6 L at 8 A.M. to 59.7 +/- 26.5 L at 8 P.M. There were diurnal variations in plasma 11-hydroxycorticosteroids (11-OHCS), mean values of which decreased 60% from 16.2 +/- 4.2 microgram/100 ml at 8 A.M. to 6.5 +/- 1.9 microgram/100 ml at 8 P.M. Sleeplessness for 24 or 48 hr under the conditions of this experiment failed to affect diurnal rhythms in aminopyrine metabolism or plasma 11-OHCS concentrations.

11-Hydroxycorticosteroids↗
PubMedDate not supplied

Prognostic value of the aminopyrine breath test in cirrhotic patients.

The aminopyrine breath test has been proposed as a quantitative test of hepatic function, but its long-term prognostic value in patients with cirrhosis has not been determined. The aim of this study was to examine the usefulness of the aminopyrine breath test in assessing prognosis and to compare it with traditional methods of evaluating liver function. One-hundred eighty-seven patients with histologically confirmed cirrhosis were studied prospectively. An aminopyrine breath test was obtained at the time of inclusion in the study and results were expressed as per cent of the dose excreted in 2 hr. At inclusion, the severity of liver disease was also assessed according to the Pugh modification of the Child-Turcotte classification based on ascites, neurological status, serum albumin, serum bilirubin and prothrombin time. Mean follow-up was 844 days. During that period, 59 of 187 patients died of their liver disease. Two-year survival decreased with increasing Child-Turcotte classification score: survival was 98% in Child Class A patients (n = 62), 66% in Child Class B (n = 76) and 36% in Child Class C (n = 49) (chi 2 = 65.6, p less than 0.001). Two-year survival also decreased significantly with increasing degree of aminopyrine breath test abnormalities: survival was 90% in patients with aminopyrine breath test greater than 4% (n = 56); 78% in patients with aminopyrine breath test = 2 to 4% (n = 66), and 43% in patients with aminopyrine breath test less than 2% (n = 65) (chi 2 = 36.9, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1977

Effects of common inhibitors of gastric acid secretion on secretagogue-induced respiration and aminopyrine accumulation in isolated gastric glands.

1. The effects of three inhibitors of gastric acid secretion, atropine, burimamide and thiocyanate, have been studied in isolated glands from the rabbit gastric mucosa. The glands were either resting or stimulated by carbachol, histamine or dibutyryl cyclic AMP. The effects were determined from changes in oxygen consumption and accumulation of the weak base aminopyrine. The latter gives an indirect measurement of the acid production in the glands. 2. Atropine (10 (-6) M) almost totally inhibited the transient response induced by carbachol (10 (-4) M) in both measured parameters. The histamine-induced increase in respiration was inhibited when the atropine concentration was raised to 10 (-4) M. To a lesser extent also, histamine-induced aminopyrine accumulation was reduced. The dibutyryl cyclic AMP stimulated oxygen consumption was not affected by atropine. 3. Burimamide competitively inhibited the histamine responses but was without effect on those of carbachol and dibutyryl cyclic AMP. 4. Thiocyanate (10 (-2) M) inhibited the increase in oxygen consumption induced by all three secretagogues but not down the prestimulatory level, in spite of total abolishment of the aminopyrine accumulation. 5. In unstimulated glands, burimamide (10 (-3) M) or atropine (10 (-4) M) did not alter the normal aminopyrine ratio (aminopyrine in intraglandular water/ aminopyrine in extraglandular water) of approximately 50. This may indicate the existence of preformed acid in resting parietal cells. Thiocyanate, on the other hand, lowered the aminopyrine ratio in unstimulated glands from 46 to 2. Possible mechanisms for the thiocyanate effect are discussed in terms of an inability to separate acid and base in the secreting membrane.

Aminopyrine↗
PubMed1984

Dietary influences on the kinetics of antipyrine and aminopyrine in human subjects.

The possible dietary influences on in vivo antipyrine and aminopyrine kinetics with reference to energy (1500, 1800, 3000 kcal) and protein (5, 10, 15, 20% protein energy-PE) intake were studied in a carefully controlled metabolic experiment in young healthy adult male volunteers aged between 25-34 years. Antipyrine and aminopyrine were used to evaluate drug metabolism. On 1500 kcal intake with 10% PE, the metabolism of both aminopyrine and antipyrine were significantly reduced whereas on 1800 kcal with 10% PE intake, only aminopyrine metabolism decreased significantly as compared to 3000 kcal with 10% PE. Antipyrine clearance on 1800 kcal with 10% PE however had not decreased to the same extent as on 1500 kcal with 10% PE. The results indicate that on low calorie intake with 10% PE, the drug metabolism is decreased. When the protein intake on 1500 kcal was doubled (20% PE) there was a significant stimulation of both aminopyrine and antipyrine metabolism. Aminopyrine and antipyrine clearances on 3000 kcal with 5% PE were significantly reduced as compared to 3000 kcal with 10% and 15% PE indicating that unlike proteins, carbohydrate and/or fat calories per se do not significantly stimulate drug metabolism. When the protein energy in the diet was increased from 5% to 10% or 15% at 3000 kcal, there was a stimulation of both antipyrine and aminopyrine metabolism. Significant differences between 10% and 15% of protein energy were not observed when the energy was adequate (3000 kcal). Therefore it is necessary to consider both proteins and energy as important variables affecting drug clearances from plasma in malnourished conditions.

Adult↗
PubMed1992

Aminopyrine breath test in the prognostic evaluation of patients with cirrhosis.

This prospective study assessed the role of aminopyrine breath test in the prognosis of patients with cirrhosis, and evaluated whether the test provided useful information not included in the Pugh score. During a period of 36 months, 125 patients with biopsy proven liver cirrhosis were included, and followed for up to 48 months (median 17 months). During follow up 43 patients died (20 of liver failure). Survival was univariately related to aminopyrine breath test (p less than 0.02), Pugh score (p less than 0.01), presence of ascites (p less than 0.01), and sex (p less than 0.05). Using Cox's regression analysis, Pugh score, aminopyrine breath test, and sex, were independent significant predictors of survival. From the Cox's model a prognostic index was computed. According to a receiver operating characteristic curve analysis, the prognostic index predicting death showed an improvement in area under the curve when compared with a prognostic index calculated excluding aminopyrine breath test, but the improvement did not reach statistical significance (p = 0.12). A similar prognostic index was calculated to predict death from liver failure. Cox's regression analysis selected aminopyrine breath test, Pugh score, and aetiology as the best set of predictor covariates. According to a receiver operating characteristic curve analysis, a prognostic index cut off value of 2.6 had a 94% sensitivity and a 88% specificity. The prognostic index significantly improved prognostic accuracy when compared with a prognostic index calculated from Pugh score and aetiology, but excluding aminopyrine breath test (p = 0.05). These data disclose that the aminopyrine breath test offers additional prognostic information to the Pugh score, and the prognosis of patients with cirrhosis.

Adult↗
PubMed1979

A sensitive gas-chromatographic assay using a nitrogen-phosphorus detector for determination of antipyrine and aminopyrine in biological fluids.

A method using gas chromatography with organic nitrogen-sensitive detection is described for measurement of antipyrine and aminopyrine concentrations in biological fluids. The analysis was performed isothermally on 3% SP-2250 DB after alkalinized saliva was extracted into chloroform. Phenacetin served as internal standard. Low oral doses of antipyrine (1.0-1.8 mg/kg) and/or aminopyrine (2 mg/kg) were measured accurately in saliva of normal human subjects. The standard curves for antipyrine and aminopyrine were linear from 0 to 10 microgram/ml. The coefficient of variation, determined at a salivary concentration of 2 microgram/ml, was 1.7% for antipyrine and 2.4% for aminopyrine. Saliva concentrations obtained by this method in normal human subjects after either an oral dose of antipyrine (18 mg/kg) or aminopyrine (9 mg/kg) agreed closely with those determined by the flame ionization gas-chromatographic method used to measure higher concentrations of antipyrine and aminopyrine. Antipyrine (1.8 mg/kg) administered concomitantly with aminopyrine (1 mg/kg or 2 mg/kg) to normal male volunteers prolonged mean saliva antipyrine half-life by about 25-33% compared to values obtained when these same subjects received the same dose of antipyrine alone.

Adult↗
PubMed1985

Effect of infant age on aminopyrine breath test results.

UNLABELLED: The aminopyrine breath test has been used in adults as a measure of hepatic N-demethylase activity. In order to study maturational changes in enzyme function, 13C aminopyrine (2 mg/kg) was administered orally to infants (n = 16) between the ages of 1 and 38 wk. Breath samples were collected for 6 h after administration of the labeled aminopyrine for the measurement of 13CO2 enrichment. Using a number of different scoring methods to quantitate 13CO2 elimination of breath, demethylation of aminopyrine was found to be positively correlated to age. By 20 wk of age, some infants had rates of elimination similar to those measured in adults. Absorption was excluded as a limiting variable, because no improvement in oxidation rates was found when the aminopyrine was readministered as an intravenous bolus. Changes in nutritional status and route of feeding (enteral versus parenteral) did not prevent the effect of maturation on aminopyrine elimination. CONCLUSIONS: 1) maturational differences are seen in the metabolism of aminopyrine; 2) these differences may reflect immaturity of N-demethylase activity or diversion of the liberated formaldehyde into biosynthetic rather than oxidative pathways.

Age Factors↗
PubMed1977

Hepatic aminopyrine N-demethylase system: effect of cyanide on microsomal N-demethylase activity.

Cyanide, an inhibitor of many hemoproteins, was shown to affect a number of microsomal drug-metabolizing activities catalyzed by cytochrome P-450. The N-demethylation reaction of aminopyrine was inhibited noncompetitively by this inhibitor in microsomal preparations from rats. The binding reaction of aminopyrine with microsomal cytochrome P-450 was also modified by cyanide, and an abnormal aminopyrine-induced difference spectrum of microsomes by cyanide, and an abnormal aminopyrine-induced difference spectrum of microsomes appeared when cyanide was added to the reaction mixture. Partial dissociation of cytochrome P-450. Cyanide complex by aminopyrine was observed by spectrophotometrical and epr spectroscopic methods. These results suggest that aminopyrine and cyanide reciprocally affect binding with cytochrome P-450 and modification by cyanide of aminopyrine binding reaction with the hemoprotein produces an inhibition of N-demethylase activity.

Aminopyrine↗
PubMed1984

The pharmacokinetic interaction of diethyl ether with aminopyrine in the rat.

Our studies in rats clearly demonstrate a significant depression of aminopyrine metabolism in vivo by ether anesthesia. The depression of aminopyrine elimination was shown both by measurements of plasma aminopyrine clearance and by depression of the [14C]aminopyrine breath test. No apparent effect of ether was seen on aminopyrine volume of distribution. The effect of ether was prolonged, as judged by its persistence in the aminopyrine breath test for 3 hr after stopping ether anesthesia. In addition, when ether was administered in combination with a single dose of ethanol, aminopyrine clearance was inhibited significantly more than with ethanol alone. These data not only have a bearing on proper methodologic design of drug clearance studies but also may relate to the effects of some anesthetics on hepatic function.

Aminopyrine↗
PubMed1992

A method to simultaneously investigate histamine-induced cyclic AMP and aminopyrine accumulation in isolated gastric mucosal cells from human biopsies.

A method has been developed to simultaneously measure two parameters of histamine-induced gastric secretion, cyclic AMP and aminopyrine accumulation, in gastric mucosal cells from human biopsies. Histamine stimulated cyclic AMP and aminopyrine accumulation with different time courses. Cyclic AMP production reached a maximum at 30 min, whereas maximal aminopyrine accumulation was obtained after the cells had been incubated for 90 min in presence of 100 mcM histamine. Histamine was more potent in stimulating aminopyrine than cyclic AMP accumulation. The ED50 values for histamine-induced aminopyrine accumulation were estimated to be 0.88 +/- 0.02 and 25.53 +/- 8.75 mcM for cyclic AMP production, respectively. The aminopyrine accumulation was more than half-maximally increased at 1 mcM histamine without significant effects on the cyclic AMP basal level. It remains to be elucidated whether this finding indicates, besides cyclic AMP, the involvement of calcium in histamine stimulus. The histamine H2-receptor antagonists cimetidine and ranitidine inhibited both in vitro parameters, whereas the gastric proton pump inhibitor omeprazole only affected aminopyrine accumulation. Our method might be a valuable tool for in vitro pharmacological and clinical investigations on histamine-induced gastric secretion in human biopsies.

Adult↗
PubMed1982

Induction of hepatic gamma-glutamyl transpeptidase in rats by repeated administration of aminopyrine.

The effect of a 20-day administration of aminopyrine (600 mg kg-1) as well as two metabolites of aminopyrine, 4-aminoantipyrine (525 mg kg-1) and 4-acetamidoantipyrine (635 mg kg-1), on several hepatic, kidney and serum enzyme activities were investigated. In the aminopyrine-treated group, a pronounced induction of gamma-glutamyl transpeptidase was shown in the whole homogenate as compared to that in the hepatic microsomes. Serum gamma-glutamyl transpeptidase activity was also increased by administration of aminopyrine or 4-aminoantipyrine. No change in gamma-glutamyl transpeptidase activity was observed in kidney and hepatic cytosolic fractions. In all cases, 4-acetamidoantipyrine treatment showed no significant change in the enzyme activities tested. Under the same experimental condition, the amounts of cytochrome P-450 and b5, the activities of aminopyrine N-demethylase, aniline hydroxylase and carboxylesterase of liver microsomes were all induced in the aminopyrine- and 4-aminoantipyrine-treated rats. The activities of NADPH cytochrome c reductase and NADH ferricyanide reductase were also increased. The results in this paper support the view that repeated administration of aminopyrine induces hepatic membrane-bound enzyme, particularly, gamma-glutamyl transpeptidase activity.

Aminopyrine↗
PubMed1981

A free radical mechanism of prostaglandin synthase-dependent aminopyrine demethylation.

The mechanism of prostaglandin synthase-dependent N-dealkylation has been investigated using an enzyme preparation derived from ram seminal vesicles. Incubation of an N-alkyl substrate, aminopyrine, with enzyme and arachidonic acid, 15-hydroperoxyarachidonic acid, or tert-butyl hydroperoxide resulted in the formation of the transient aminopyrine free radical species. Formation of this radical species, which was detected by electron paramagnetic resonance spectroscopy and/or absorbance at 580 nm, was maximal approximately 30 s following initiation of the reaction and declined thereafter. Free radical formation corresponded closely with formaldehyde formation in this system, in terms of dependence upon substrate and cofactor concentration, as well as in terms of time course. Both aminopyrine free radical and formaldehyde formation were inhibited by indomethacin and flufenamic acid, inhibitors of prostaglandin synthase. The results suggest that the aminopyrine free radical is an intermediate in the prostaglandin synthase-dependent aminopyrine N-demethylase pathway. The aminopyrine free radical electron paramagnetic resonance spectrum revealed that this species is a one-electron oxidized cation radical of the parent compound. A reaction mechanism has been proposed in which aminopyrine undergoes two sequential one-electron oxidations to an iminium cation, which is then hydrolyzed to the demethylated amine and formaldehyde. Accordingly, the oxygen atom of the aldehyde product is derived from neither molecular nor hydroperoxide oxygen, but from water.

Aminopyrine↗
PubMed1977

[The aminopyrine respiratory test under the acute effect of ethanol. Evaluation of a new method for the measurement of microsomal functions of the liver].

Microsomal demethylation, a partial function of the liver, can be estimated by the aminopyrine breath test. Both the determination of specific activity and the disappearance rate constant for 14CO2 in breath demand the assumption of rapid formaldehyde oxidation to CO2. Conversely, the disappearance of aminopyrine from plasma reflects microsomal aminopyrine metabolism only. Ethanol is known to affect both microsomal demethylation and formaldehyde metabolism. If in the presence of ethanol the latter process should become rate-limiting, a discrepancy between the data obtained in breath and in plasma could be expected. In order to investigate this possibility 10 fasting healthy male volunteers received 9 mg/kg (dimethylamine-14C)-aminopyrine (2 muCi) orally and, 3 hs later, 0.7 g/kg ethanol. Immediately following ethanol the specific activity of 14CO2 in breath decreased by 25% (p less than 0.005) and the disappearance of 14CO2 from breath was 31% lower than in 17 matched controls (p less than 0.005). The aminopyrine plasma disappearance rate, determined by GLC, decreased by 30% after ethanol (p less than 0.05). Since the decrease in aminopyrine plasma disappearance rate seems to account for the proportional decreases obtained by breath analysis, it is concluded that the aminopyrine breath test expresses the rate of microsomal demethylation even during altered formaldehyde metabolism, e.g. in acute ethanol intoxication.

Aminopyrine↗
PubMed1988

Effect of glutathione depletion on aminopyrine and formaldehyde metabolism.

In previous studies, diethylmaleate (DEM)- and phorone-induced hepatic glutathione (GSH) depletion in rats was accompanied by impaired evolution of 14CO2 from the N-14C-labeled methyl groups of aminopyrine, which in turn was attributed to impaired generation of formaldehyde, its subsequent oxidation to formate, or to some combination of both. In the present study, l-buthionine sulfoximine (BSO)-induced hepatic GSH depletion was also accompanied by decreased evolution of CO2 from aminopyrine, but the extent of the fall in CO2 was less than that induced by DEM or phorone, even though the decrease in hepatic GSH was comparable with all three GSH-lowering compounds. Incubation of freshly prepared normal hepatic microsomes in vitro with the GSH-lowering agents resulted in impaired aminopyrine-N-demethylase (APDM) activity with inhibition by phorone greater than DEM greater than BSO. By contrast, hepatic microsomes prepared from rats pretreated with these compounds had normal APDM activity. 14CO2 evolution from i.p. administered [14C]formaldehyde was not impaired by any of the GSH-lowering compounds. Thus, assessment of APDM activity and formaldehyde metabolism did not unequivocally establish the mechanism(s) by which CO2 evolution from aminopyrine is depressed by DEM, phorone and BSO, although low GSH is likely to impair metabolism of formaldehyde formed in liver after demethylation of aminopyrine. Quantitative differences in the degree of depression of CO2 evolution suggest that at least DEM and phorone exert an additional inhibitory effect by a GSH-independent mechanism. This may involve inhibition of aminopyrine-N-demethylase activity.

Aminopyrine↗