Disposition of nicotine and eight metabolites in smokers and nonsmokers: identification in smokers of two metabolites that are longer lived than cotinine.

The disposition of a single intravenous dose of 14C-nicotine was investigated in six cigarette smokers and six nonsmokers. Plasma and urinary elimination of both nicotine and cotinine was faster in smokers than in nonsmokers. In the urine of both smokers and nonsmokers, we identified nicotine and eight metabolites, including two new metabolites: metabolite A (3-hydroxycotinine glucuronide) and metabolite G (demethylcotinine delta 2',3'-enamine). Metabolites A and G were of particular interest because, in smokers, they both persisted longer than cotinine. This property renders them more sensitive than cotinine as potential indicators of passive exposure to cigarette smoke.

Kinetics of conjugation and oxidation of nitrobenzyl alcohols by rat hepatic enzymes.

Previous work has suggested that quantitative differences in the in vitro and in vivo metabolism of mononitrotoluene isomers are a result of differences in the hepatic conjugation and oxidation of the first metabolic intermediates, the mononitrobenzyl alcohols. We have determined the steady-state kinetic parameters, Vmax, Km and V/K, for the metabolism of the nitrobenzyl alcohols by rat hepatic alcohol dehydrogenase, glucuronyltransferase, and sulfotransferase. 3-Nitrobenzyl alcohol was the best substrate for cytosolic alcohol dehydrogenase (Vmax = 1.48 nmoles/min/mg protein, V/K = 3.15 X 10(-3) nmoles/min/mg protein/microM, Km = 503 microM). Vmax and Km values for 4-nitrobenzyl alcohol were similar, but V/K was about 60% of that for 3-nitrobenzyl alcohol. 2-Nitrobenzyl alcohol was not metabolized by the alcohol dehydrogenase preparation used here, but it was metabolized to 2-nitrobenzoic acid by a rat liver mitochondrial preparation. 2-Nitrobenzyl alcohol was the best substrate for microsomal glucuronyltransferase (Vmax = 3.59 nmoles/min/mg protein, V/K = 11.28 X 10(-3) nmoles/min/mg protein/microM, Km = 373 microM). The Vmax for 3-nitrobenzyl alcohol was similar, but the V/K was about half and the Km was about twice that for 2-nitrobenzyl alcohol. The Vmax for 4-nitrobenzyl alcohol was about 40% and the V/K was about half that for 2-nitrobenzyl alcohol. The best substrate for cytosolic sulfotransferase was 4-nitrobenzyl alcohol (Vmax = 1.69 nmoles/min/mg protein, V/K = 37.21 X 10(-3) nmoles/min/mg protein/microM, Km = 48 microM). The Vmax values for the other two benzyl alcohols were similar, but the V/K and Km values were about 11 and 400%, respectively, of those for 4-nitrobenzyl alcohol. These data are in qualitative agreement with results obtained when the nitrobenzyl alcohols were incubated with isolated hepatocytes, but they do not allow quantitative modeling of the data from hepatocytes.

A further study of FTC yield and nicotine absorption in smokers.

The relationship between nicotine yield as determined by the FTC method and nicotine absorption was examined in 72 smokers in a more rigorous repetition of a previous study of 33 smokers. For this study, 113 smokers evenly distributed across four FTC "tar" yield ranges were recruited, only 72 demonstrated reasonable compliance with the study criteria with regard to sample collections and cigarette brand style consistency. Subjects recorded the number of cigarettes smoked daily and collected a 24-h urine sample and a saliva sample on 3 consecutive days. Nicotine absorption was determined by monitoring urinary excretion of nicotine and its metabolites. In addition, saliva samples were monitored for cotinine using radioimmunoassay (RIA). The correlation of the relationship for nicotine absorbed per cigarette was positive and significant (r = 0.31, P = 0.008) but weaker than in the previous study. Only smokers in the highest yield range showed any statistical difference from smokers in the lower ranges. Our results suggest that FTC nicotine yield is weakly related to nicotine absorption and that smoker-controlled factors exert a great influence on the amount of nicotine absorbed by smokers. Compensation is substantial but incomplete for the minority (by market share) of smokers at the low end of the yield scale. It is uncertain how well any alternative set of machine parameters would predict nicotine absorption for the majority of smokers, even if it were more predictive for the small number of smokers at the lower yield part of the range.

Comparison of measured and FTC-predicted nicotine uptake in smokers.

Cigarette smokers have a wide variety of "tar" and nicotine yields to choose from in the current market, ranging from 0.5 mg "tar" and less than 0.05 mg nicotine to 27 mg "tar" and 1.8 mg nicotine by the Federal Trade Commission (FTC) method. To understand better the relationship between FTC nicotine yields and actual nicotine uptake in smokers, we have studied nicotine uptake in 33 smokers of self-selected products representing four "tar" groupings: 1 mg "tar" (1MG), ultra-low "tar" (ULT), full-flavor low "tar" (FFLT), and full flavor (FF) cigarettes. These cigarette categories had mean FTC nicotine yields of 0.14, 0.49, 0.67, and 1.13 mg/cigarette, respectively. The subjects smoked their usual brand of cigarette ad libitum and provided a 24-h urine sample for total nicotine uptake analysis over a period during which the number of cigarettes smoked was recorded. Nicotine uptake was determined by monitoring urinary nicotine and its metabolites, including the glucuronide conjugates. Daily nicotine uptake was 9.1 +/- 7.3 mg (range 1-21 mg) for 1MG, 19.2 +/- 10.0 mg (range 4-42 mg) for ULT, 21.8 +/- 9.4 mg (range 13-38 mg) for FFLT, and 37.1 +/- 14.4 mg (range 21-60 mg) for FF smokers. On a per cigarette basis, yields were 0.23 +/- 0.11, 0.56 +/- 0.23, 0.60 +/- 0.18, and 1.19 +/- 0.43 mg nicotine, respectively. Although individual variability was fairly large (CVs of 0.39-0.80), means for the different groups showed that lower FTC yield smokers not only absorb less nicotine per 24-h period, but also per cigarette smoked. These data suggest that nicotine uptake is a function of individual smoking behavior within product design limits. We conclude from these data that, while FTC yield cannot precisely predict nicotine uptake for an individual smoker, it is useful in predicting and comparing actual nicotine uptake by smokers who select cigarettes with a particular FTC yield.

Intragastric nitrosation of nicotine is not a significant contributor to nitrosamine exposure.

To determine the potential for intragastric nicotine nitrosation, we carried out a kinetic study of the reaction of nicotine with nitrous acid in aqueous solution. The reaction of nicotine with nitrous acid resulted in the formation of three products, NNA, NNN, and NNK. The three parallel reactions were first order of 10-6 L/mol/s. The optimum pH range for formation of NNA, NNN, and NNK was 2.4 to 3.1. Thiocyanate (100 mM) slightly increased the rate of formation of NNN and NNK but tripled the rate of formation of NNA at pH 3.5 at 37 degrees C. We have also studied the nitrosation of pseudooxynicotine, a bacterial and fungal metabolite of nicotine. This secondary amine nitrosated rapidly to produce NNK. Our proposed mechanism for the conversion of nicotine to NNK includes nine kinetically distinct steps and is in agreement with our experimental results. The rate limiting step involves the formation of nicotine-1',2'-iminium ion. This ion hydrolyzes to form pseudooxynicotine which undergoes rapid, irreversible nitrosation to NNK. Given the very slow rate of nicotine nitrosation, it is unlikely that nicotine itself contributes to exposure to nitroso compounds due to chemically mediated intragastric nitrosation.

Chemical and biological studies of a cigarette that heats rather than burns tobacco.

Cigarettes can be developed that heat rather than burn tobacco. Such products would be expected to have less "tar" and other combustion products than cigarettes that burn tobacco. With one product of this type, benzo(a)pyrene, N-nitrosamines, phenolic compounds, acetaldehyde, acrolein, hydrogen cyanide, and N-heterocyclic compounds have been reduced 10- to 100-fold compared to the Kentucky reference (1R4F) cigarette, a representative low-tar cigarette. The yields of nicotine and carbon monoxide from this new cigarette are less than the yields of 95% and 75%, respectively, of the cigarettes sold in the United States during 1988. Nicotine absorption from smoking this new cigarette is not significantly different from that of tobacco-burning cigarettes yielding equivalent levels of nicotine. The urine mutagenicity of smokers of new cigarettes is significantly less (P less than .05) than that of smokers of tobacco-burning cigarettes and is not significantly different (P greater than .10) from that of nonsmokers. We conclude that cigarettes which heat rather than burn tobacco can reduce the yield of tobacco combustion products. This simplification of smoke chemistry had no effect on nicotine absorption in smokers and resulted in a reduction of biological activity in smokers as measured by urine mutagenicity.

Human urine mutagenicity study comparing cigarettes which burn or only heat tobacco.

Cigarette smokers have been reported to void urine which is more mutagenic, as measured in the Ames bacterial mutation assay, than urine voided by non-smokers. Condensate from the mainstream smoke of a cigarette which heats, but does not burn tobacco (test cigarette) showed no evidence of mutagenicity in a battery of in vitro genotoxicity assays under conditions in which condensate from the mainstream smoke of cigarettes that burn tobacco was mutagenic. The objective of this study was to determine whether the absence of mutagenic activity observed in the in vitro assays would be reflected in the urine of smokers of the test cigarette. 72 subjects (31 smokers and 41 non-smokers) were enrolled in a 6-week study, with the smokers randomly divided into 2 groups. The study was designed as a double crossover, with each smoker smoking both test (tobacco-heating) and reference (tobacco-burning) cigarettes. This design allowed each smoker to serve as his or her own control while at the same time allowing comparisons between groups of non-smokers and smokers of both test and reference cigarettes. 24-h urine samples were collected twice a week and concentrated using XAD-2 resin. Urine concentrates were tested in Ames bacterial strains TA98 and TA100, with and without metabolic activation and with and without beta-glucuronidase/aryl sulfatase. Individuals who smoked the test cigarette voided urine which was significantly less mutagenic than that voided when they smoked reference cigarettes. The mutagenicity of urine from smokers who smoked the test cigarette and non-smokers did not differ under any of the assay conditions used in this study.

Dietary nicotine: a source of urinary cotinine.

Foods, principally from plants in the family Solanaceae, and a number of teas were examined for the presence of nicotine. Dietary nicotine would give rise to cotinine in urine and compromise estimates of exposure to tobacco smoke that depend on urinary cotinine. All foods were homogenized, extracted and analysed for nicotine and cotinine by gas chromatography with nitrogen-sensitive detection (GC) and/or GC/MS (mass spectrometry). Weak acid and aqueous extracts of the teas were analysed in a similar manner. Nicotine was not detected (less than 1 ng/ml of extract) in egg plant or green pepper. The average values for nicotine in tomato and potato were 7.3 ng/g wet weight and 15 ng/g wet weight, respectively. Black teas, including regular and decaffeinated brands, had nicotine contents ranging from non-detectable to greater than 100 ng/g wet weight. Instant teas yielded the highest nicotine contents observed (up to 285 ng/g wet weight). The possible sources of nicotine in these foods are discussed. A range of potential values for urinary cotinine concentrations (0.6 to 6.2 ng/ml) was calculated based upon estimated average and maximal consumptions of these foods and beverages. Because of the potential for exposure to nicotine by way of these routes, the use of urinary cotinine as a biomarker of exposure to environmental tobacco smoke may be compromised.

Absorption and disposition of 14C-labelled Kathon biocide, a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one, following intravenous or dermal administration to male Sprague-Dawley rats.

Kathon biocide (KB), a 75:25 mixture of 5-chloro-2-methyl-4-isothiazolin-3-one (KI) and 2-methyl-4-isothiazolin-3-one (KII), is a broad-spectrum antimicrobial agent. The absorption and disposition of 14C label were studied in male Sprague-Dawley rats following iv or dermal administration of KB 14C labelled in the carbonyl carbon of either KI or KII. KI-labelled Kathon was distributed rapidly following an iv dose (0.8 mg/kg). Total 14C label in the plasma was rapidly eliminated, with the data best described by a three-compartment model. Total 14C label concentration in the blood, however, remained constant at 3 ppm from 6 to 96 hr after administration and represented 29% of the dose, indicating that KI-labelled Kathon and/or metabolites was sequestered by the cellular fraction of blood. Elimination of 14C label from the tissues examined was biphasic, with a terminal half-life of more than 4 days; by 96 hr, faeces, urine and CO2 accounted for 35, 31 and 4% of the dose, respectively. Following a single 24-hr dermal application of 0.2 ml of an aqueous solution containing 2000 ppm [14C]KB (400 micrograms), rats absorbed 94% of KI-labelled KB and 82% of KII-labelled KB. However, the systemic bioavailability of KB was substantially less than this, since approximately half of the absorbed KB was associated with the skin at the application site 24 hr after the application. Percutaneous absorption was not affected by concentration over the range 500-4000 ppm. As the concentration of KI-labelled KB in the applied solution increased from 500 to 4000 ppm, the relative amount of 14C label associated with the skin decreased, while that in the excreta increased, indicating greater systemic penetration at higher concentrations. Low amounts of 14C label were found in the testes (less than 2 ppb) and blood (24 ppb) 28 days after a single dermal application of KI-labelled KB. Four consecutive daily applications of KI-labelled KB did not influence the proportion of the dose absorbed from the skin. However, the proportion of the dose excreted was higher than after a single application of an equivalent amount of KB.

A specific gas chromatographic analysis for cysteinyl-S-sulfonate residues in physiologically significant proteins treated with sulfite.

It has been shown in previous studies that when sulfite is absorbed by rabbits via either inhalation of SO2 or oral exposure to sulfite, the hydrated form, bisulfite, interacts with plasma disulfides where it is suspected to be in the form, cysteine-S-sulfonate. A rapid and specific gas chromatographic analysis procedure for cysteine-S-sulfonate has been developed to better study the distribution of sulfite in biological systems. Sulfonated proteins are enzymatically hydrolyzed to ensure stability of the acid labile S-sulfonate disulfide. The hydrolysate is then applied to a 6 cm cation-exchange column and eluted with 0.1 N HCl, which elutes the acidic cysteine-S-sulfonate with the void volume of the column, leaving behind any remaining cysteine. The silylated derivatives of the column effluent are prepared using Tri-Sil/BSA. These derivatives are injected into a gas chromatograph equipped with a flame-photometric detector operating in the sulfur mode, 2% OV-101 on Chromosorb W/HP 1/4 inch glass column, oven temperature 140 degrees C, and carrier flow rate of 86 mL/min. The presence of cysteine-S-sulfonate in sulfite-treated rabbits has been directly determined by the described method.

A new quantitative thermospray LC-MS method for nicotine and its metabolites in biological fluids.

A rapid thermospray liquid chromatography-mass spectrometry (TSP LC-MS) method is described for the simultaneous determination of nicotine and 17 of its metabolites. Chemical ionization of nicotine and its metabolites separated by reversed-phase HPLC is achieved by postcolumn addition of ammonium acetate buffer with the filament of the ion source turned off. Quantification is accomplished by selectively monitoring the unique protonated molecular ion of each metabolite. Trideuterated cotinine serves as an internal standard. Linear responses for cotinine, demethylcotinine, and trans-3'-hydroxycotinine were observed over a concentration range of 20-8000 ng/mL, and 80-8000 ng/ml for nicotine and nicotine-1'-N-oxide. Of the 17 metabolites examined, only nicotine, cotinine, demethylcotinine, and trans-3'-hydroxycotinine were detected in smokers' urine.

Unique purified hydrated-gelatin diet for feeding dietary fiber to Wistar rats.

A purified hydrated gelatin diet was developed for feeding dietary fibers to Wistar rats. A dry fiber mix was prepared that consisted of 54.91 dextrose, 13.80 casein, 2.97 AIN mineral mix, 1.28 AIN vitamin mix, 0.17 dl-methionine, 6.80 lard and 5.10 gelatin (g/100g total dry feed). Either cellulose, hemicellulose, lignin, or pectin (15 g/100 g total dry feed) was added to the hydrated dry fiber mix and blended until complete distribution and hydration of the fiber was achieved. After gelling, these hydrated diets were stable for up to 24 hours in environmental conditions commonly encountered in animal facilities. Gel weep was minimal thus permitting feed consumption to be monitored conveniently by weighing the residue in the feeders. In situ examination of stomach contents after feeding such hydrated diets to rats indicated that the gelatin gel was readily degraded and did not confound gel formation by fiber itself. Feed efficiency values (g gain/100 kcal digestible energy) for these diets following a 26-day feeding trial were as follows: no fiber, 6.21; cellulose, 6.38; hemicellulose, 6.23; lignin, 6.52; and pectin, 5.53.

Sequential enzyme-catalyzed metabolism of 4-nitrotoluene to S-(4-nitrobenzyl)glutathione.

[14C]-4-Nitrotoluene was metabolized by rat liver postmitochondrial supernatant containing NADPH, reduced glutathione and a sulfate activating system to 4-nitrobenzyl alcohol, 4-nitrobenzyl sulfate, and S-(4-nitrobenzyl) glutathione. Formation of both sulfur-containing metabolites was dependent on the presence of a sulfate activating system. These results suggest that the glutathione conjugate was derived from 4-nitrobenzyl sulfate. Reaction of 4-nitrobenzyl sulfate with glutathione was not detected in pH 7.4 buffer, but rat liver cytosol catalyzed the formation of the glutathione conjugate from 4-nitrobenzyl sulfate. These results show that 4-nitrotoluene is metabolized in rat liver by sequential side chain oxidation, sulfation, and glutathione conjugation. Furthermore, they indicate that, unlike certain other arylmethyl sulfates, 4-nitrobenzyl sulfate is not highly reactive.

Metabolism of nitrotoluenes by freshly isolated Fischer 344 rat hepatocytes.

2-Nitrotoluene (2NT), but not 3-nitrotoluene (3NT) or 4-nitrotoluene (4NT), is genotoxic in the in vivo-in vitro hepatic DNA repair assay. These differences in genotoxicity may be due to hepatic metabolism. For this reason, the metabolism of the nitrotoluenes was compared in hepatocytes isolated from male Fischer 344 rats. Hepatocytes were incubated with [U-14C]2NT, 3NT, or 4NT at concentrations from 25 to 1000 microM for up to 60 min. Metabolites were separated by reverse phase HPLC and identified by coelution with standards on HPLC, specific enzyme hydrolysis, and GC-MS analysis. 2NT was converted to 2-nitrobenzyl alcohol (52%), 2-nitrobenzyl alcohol glucuronide (28%), an unidentified metabolite (20%), and 2-nitrobenzoic acid (3%). Metabolites from 3NT were 3-nitrobenzoic acid (56%), 3-nitrobenzyl alcohol (29%), and 3-nitrobenzyl alcohol glucuronide (13%). 4NT was metabolized to S-(4-nitrobenzyl)glutathione (68%), 4-nitrobenzyl alcohol (12%), sulfate and glucuronide conjugates of 4-nitrobenzyl alcohol (6%), and 4-nitrobenzoic acid (2%) (expressed as percentage of total metabolism). The formation of the respective nitrobenzyl alcohols by hepatocytes was linear with respect to time for 15-20 min. The formation of other metabolites was linear over a 45-min incubation period. Incubation of 2NT, 3NT, or 4NT (1 mM) with rat hepatic microsomes produced only the respective nitrobenzyl alcohols and the rate of formation was linear for 90 min. The data suggest that each nitrotoluene isomer is metabolized to the corresponding benzyl alcohol, but that substantial differences in the metabolism of the benzyl alcohols exist.

A physiologically based pharmacokinetic model for nicotine disposition in the Sprague-Dawley rat.

A physiologically based pharmacokinetic (PBPK) model was developed to describe the disposition of nicotine in the Sprague-Dawley (SD) rat. Parameters for the model were either obtained from the literature (blood flows, organ volumes) or determined experimentally (partition coefficients). Nicotine metabolism was defined in the liver compartment by the first-order rate constants KNC and KNP which control the rate of nicotine metabolism to cotinine and "polar metabolites" (PM), respectively. These rate constants were estimated by optimizing the model fit to pharmacokinetic data obtained by administering an intraarterial (S)-[5-3H]nicotine bolus of 0.1 mg/kg to 6 rats. Model simulations that optimized for the appearance of cotinine in plasma estimated KNC and KNP to be 75.8 and 24.3 hr-1, respectively. Use of these constants in the model allowed us to accurately predict nicotine plasma kinetics and the fraction of the dose eliminated by renal (8.5%) and metabolic (91.5%) clearance. To validate the model's ability to predict tissue kinetics of nicotine, 21 male SD rats were administered 0.1 mg/kg (S)-[5-3H]nicotine intraarterially. At seven time points following treatment, 3 rats were euthanized and tissues were removed and analyzed for nicotine. Model-predicted nicotine tissue kinetics were in agreement with those determined experimentally in muscle, liver, skin, fat, and kidney. The brain, heart, and lung exhibited nonlinear nicotine elimination, suggesting that saturable nicotinic binding sites may be important in nicotine disposition in these organs. Inclusion of saturable receptor binding expressions in the mathematical description of these compartments resulted in better agreement with the experimental data. The Bmax and KD estimated by model simulations for these tissues were brain, 0.009 and 0.12; lung, 0.039 and 2.0; and heart, 0.039 nmol/tissue and 0.12 nM, respectively. This PBPK model can successfully describe the tissue and plasma kinetics of nicotine in the SD rat and will be a useful tool for pharmacologic studies in humans and experimental animals that require insight into the plasma or tissue concentration-effect relationship.

Sexual dimorphism of nicotine metabolism and distribution in the rat. Studies in vivo and in vitro.

Interpretation of sex differences in nicotine metabolism and disposition in rats required studies both in vivo and in vitro to provide both metabolic and pharmacokinetic data. In each of four rat strains studied in vitro, males metabolized nicotine faster than did females. In Sprague-Dawley rats, studies of nicotine kinetics after a single iv dose of [14C]nicotine revealed a larger nicotine volume of distribution in females than in males. A prolonged plasma nicotine half-life in females balanced the larger volume of distribution, so that no sex difference appeared in plasma clearance of nicotine. Nevertheless, sex differences in nicotine metabolism are indicated inasmuch as 1) females had lower plasma cotinine concentrations than did males; 2) urinary recoveries of nicotine were higher in female than in male rats; 3) total urinary output of nicotine metabolites was higher in male than female rats, consistent with the enhanced N- and C-oxidation of nicotine by male rats observed in vitro. In female rats the reduced rate of nicotine metabolism, as well as a larger volume of distribution of nicotine, explains in part the reported increased lethality of female compared with male rats.

Pharmacokinetics of nicotine and 12 metabolites in the rat. Application of a new radiometric high performance liquid chromatography assay.

A new radiometric assay for nicotine and 12 of its metabolites disclosed that plasma nicotine and cotinine t1/2 beta were independent of dose after single intraarterial nicotine doses of 0.1, 0.5, or 1.0 mg/kg. At high doses, nicotine AUC and clearance tended to exhibit a small degree of dose dependency. The longest lived metabolites, cotinine-N-oxide and a previously unidentified metabolite now revealed to be allohydroxydemethylcotinine, persisted for 96 hr after nicotine injection, whereas cotinine was detected for only 48 hr. Cotinine, formerly considered the longest lived nicotine metabolite, serves widely as the most sensitive indicator of prior exposure to small concentrations of nicotine. The present studies disclose new, longer lasting metabolites that may perform this function more sensitively, at least in the rat. At the 3 doses of nicotine administered, plasma nicotine half-life ranged from 0.9 to 1.1 hr; total body clearance of nicotine ranged from 2.9 to 3.9 liters.hr-1.kg-1; and apparent volume of distribution of nicotine from 4.7 to 5.7 liters.kg-1. Also at these 3 doses, mean half-lives of urinary excretion of cotinine, cotinine-N-oxide, and allohydroxydemethylcotinine ranged from 4.8 to 5.3 hr, from 7.9 to 8.2 hr, and from 9.9 to 11.0 hr, respectively.

Radiometric-high-performance liquid chromatographic assay for nicotine and twelve of its metabolites.

A sensitive, reproducible radiometric-high-performance liquid chromatographic assay has been developed to measure concentrations of nicotine and twelve of its metabolites in biological fluids. Following administration of nicotine ([2-14C]pyrrolidine) to rats, the assay was used in a pharmacokinetic investigation.

The disposition and metabolism of acrylic acid and ethyl acrylate in male Sprague-Dawley rats.

Following oral dosing of [2,3-14C]acrylic acid (AA; 4, 40, or 400 mg/kg) and [2,3-14C]ethyl acrylate (EA; 2, 20, or 200 mg/kg), the dosed radioactivity was rapidly excreted, with 50-75% of the dose for both compounds eliminated within 24 hr. The primary excretory metabolite for both compounds is carbon dioxide, accounting for 44-68% of the dose. HPLC analysis of the urine of AA- and EA-dosed animals indicated the presence of 3-hydroxypropionic acid. The detection of this metabolite suggests the incorporation of AA into propionic acid metabolism and may explain the rapid evolution of carbon dioxide from AA and EA. HPLC analysis of urine from EA-dosed rats revealed the presence of two metabolites derived from glutathione conjugation, N-acetyl-S-(carboxyethyl)cysteine and N-acetyl-S-(carboxyethyl)cysteine ethyl ester. The excretion of the N-acetyl cysteine derivatives of EA, expressed as a percentage of the dosed compound, decreased in a dose-dependent manner that may be attributed to the depletion of glutathione in organs primarily responsible for glutathione conjugation. No significant decrease in hepatic nonprotein sulfhydryl (NPSH) content was observed following oral dosing with EA at 2-200 mg/kg. However, the depletion of NPSH content at the dosing site, forestomach, and glandular stomach, decreased significantly between 0.02 and 0.2% EA in the dose solution (2 and 20 mg/kg). This observation would suggest that the dosing site represents a significant site of conjugation for relatively low doses of EA. Treatment with the carboxylesterase inhibitor, tri-o-cresyl phosphate (TOCP), 18 hr prior to acrylate dosing potentiated the depletion of hepatic nonprotein sulfhydryls, emphasizing the dominance of hydrolysis as a systemic detoxifying mode in this species. In contrast to EA, AA did not significantly decrease NPSH content in the liver, blood, or forestomach at oral doses of less than 8% AA in the dose solution (400 mg/kg), although a significant depletion of NPSH was observed in the glandular stomach at doses greater than 0.08% (4 mg/kg). No conjugation involving the double bond of AA could be detected in in vitro reactions with glutathione or in the in vivo metabolites, suggesting a secondary effect of AA on NPSH content in these organs. The weights of the forestomach and glandular stomach increased with AA dose, reflecting gross edema and inflammation. With EA this effect on organ weight was only demonstrated in the forestomach, and the response was increased when hydrolysis of EA was inhibited with TOCP.(ABSTRACT TRUNCATED AT 400 WORDS)