The pharmacokinetics of repetitive benzene exposures at 300 and 100 ppm in AKR Mice and Sprague-Dawley rats

Groups of AKR Mice and Sprague-Dawley rats were exposed to either 300 or 100 ppm benzene for 6 hr/day × 5 days/week for 20 days. The uptake and clearance of benzene was followed in blood during and after the 1st, 6th and 20th exposures. In rats, the maximum concentrations of benzene in blood (C_max) were proportional to the exposure concentrations, that is the C_max values at 300 ppm were three times the C_max values at 100 ppm. This was not the case with the mice which showed C_max values at 300 ppm equal to five to eight times the C_max values at 100 ppm. At both exposure levels mice exhibited larger elimination rate constants than rats. Both rats and mice showed larger elimination rate constants at 100 ppm than at 300 ppm. At 300 ppm, the mice showed progressive increases in elimination rate constants, progressive decreases in C_max and an unusual shift from monoexponential clearance to biexponential clearance between the 6th and 20th exposures. It is postulated that the induction of benzene-metabolizing enzymes and/or an increase in lipid tissue mass are responsible for the progressive changes of the kinetic parameters of the mice.     

The hematotoxic effects of inhaled benzene on peripheral blood,bone marrow,and spleen cells are increased by ingested ethanol

For 13 weeks, groups of $\text{C57Bl}\text{6J}$ male mice were exposed to 300 ppm benzene by inhalation, 6 hr/day, 5 days/week, and to 5 or 15% ethanol in the drinking water, 4 days/week. The number and type of blood cells in the peripheral blood, marrow, and spleen were determined at regular intervals. Anemia and lymphocytopenia were observed in the peripheral blood of all benzene and benzene/ethanol-treated groups. These cytopenias, however, were more severe in the benzene/ethanol-treated mice. In addition, there was a transient increase of normoblasts in the peripheral blood of benzene/ethanol-treated mice which was not observed in mice treated with benzene alone or in control mice. Groups exposed to benzene or benzene/ethanol displayed reduced marrow and splenic cellularities but the reductions were more severe in mice exposed to benzene/ethanol. Specifically, these reduced cellularities were characterized by decreased numbers of lymphocytes in both marrow and spleen and decreased numbers of granulocytes and normoblasts in the marrow. In benzene/ethanol-treated mice a transient increase in the numbers of splenic normoblasts was observed which coincided with the transient appearance of normoblasts in the peripheral blood of these animals. This condition was not observed in mice treated with only benzene or only ethanol. Mice exposed to benzene/ethanol presented a greater degree of atypical cellular morphology than mice treated with benzene alone. These data suggest that the ingestion of ethanol increases the hematotoxicity of inhaled benzene.     

Benzene disposition in the rat after exposure by inhalation.

Little information is available on benzene disposition after exposure by inhalation despite the importance of this route in man. Benzene metabolites as a group have been measured in bone marrow, but quantitation of individual metabolites in this target tissue has not been reported. Male Fischer-344 rats were exposed to 500 ppm benzene in air and the uptake and elimination was followed in several tissues. Concentrations of free phenol, catechol, and hydroquinone in blood and bone marrow were also measured. Steady-state concentrations of benzene (11.5, 37.0, and 164.0 μg/g in blood, bone marrow, and fat, respectively) were achieved within 6 hr in all tissues studied. Benzene half-lives during the first 9 hr were similar in all tissues (0.8 hr). A plot of amount of benzene remaining to be excreted in the expired air was biphasic with $\text{t}\text{1}\text{2}$ values for the α and β phases of 0.7 and 13.1 hr, respectively. Phenol was the main metabolite in bone marrow at early times (peak concentration, 19.4 μg/g). Catechol and hydroquinone predominated later (peak concentrations, 13.0 and 70.4 μg/g, respectively). Concentrations of these two metabolites declined very slowly during the first 9 hr. These data indicate that free catechol and hydroquinone persist in bone marrow longer than benzene or free phenol.     

Decreased in vivo acetaldehyde oxidation and hepatic aldehyde dehydrogenase inhibition in C57BL and DBA mice treated with carbon tetrachloride

Male $\text{C57BL}\text{6J}$ (C57) and $\text{DBA}\text{2J}$ (DBA) mice were dosed with 500 μl/kg ig CCl₄, 24 hr before a 3.25 g/kg ip dose of ethanol. The relative bioavailability of CCl₄ was similar in both mouse strains. CCl₄ pretreatment produced genotypically related decreases in blood ethanol elimination rates with DBA mice showing the greater decrease. Blood acetaldehyde concentrations were significantly elevated in the CCl₄-pretreated animals of both strains. DBA CCl₄-pretreated mice exhibited significantly higher blood acetaldehyde concentrations than C57 mice 1, 2, 3, and 4 hr after ethanol administration. CCl₄ pretreatment resulted in acetaldehyde elevations of approximately threefold in C57 mice four- to fivefold in DBA mice. Four hours after the ethanol dose, animals were sacrificed for enzymatic analyses of hepatic aldehyde dehydrogenase (ALDH) and alcohol dehydrogenase (ADH) activity. The specific activities and activity per gram of cytosolic and mitochondrial ALDH were decreased in both mouse strains. ADH activity was not significantly altered by CCl₄ pretreatment. Liver necrosis, as measured by serum alanine aminotransferase activity, was similar in both strains (approx fivefold increase). These data indicate that CCl₄ increased blood acetaldehyde concentrations by inhibiting hepatic cytosolic and mitochondrial ALDH and that the degree of blood acetaldehyde elevation is different in the two inbred mouse strains C57 and DBA.     

Tin distribution in adult and neonatal rat brain following exposure to triethyltin

The uptake, distribution, and elimination of tin were determined in adult and neonatal (Postnatal Day 5) rat brain following ip administration of triethyltin bromide (TET). Groups of five adult CD rats were killed at 10 min, 1 hr, 4 hr, 24 hr, 5 days, or 10 days following acute exposure to 6.0 mg/kg TET; an additional group of adult animals was killed at 24 hr following exposure to either 3.0, 6.0, or 9.0 mg/kg (N = 5/dosage). The time course for tin distribution in 5-day-old rat pups was determined by killing pups 10 min, 30 min, 1 hr, 4 hr, 8 hr, 12 hr, 24 hr, 5 days, 10 days, or 22 days following exposure to either 3.0 or 6.0 mg/kg TET (N = 4/dosage/time). Tin analyses were performed by flameless atomic absorption spectrophotometry. The $\text{t}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for total tin in the adult rat brain following 6.0 mg/kg TET was determined to be 8.0 days. The maximum concentration in the adult was reached at 24 hr and corresponded to 4.6, 9.6, and 16.6 ng tin/mg protein for dosages of 3.0, 6.0, and 9.0 mg/kg, respectively. Tin was evenly distributed across all brain areas studied. For animals exposed to 6.0 mg/kg TET on Postnatal Day 5, the $\text{t}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for total tin in the brain was 7.3 days. A maximum concentration of 9.9 ng tin/mg protein was reached at 8 hr postexposure. The rate of elimination of tin from the brain (as measured by the elimination rate constant k_el) did not differ significantly between adults and neonates. However, due to a dilution effect by the rapid brain growth of the neonate, the concentration of tin in the neonatal brain following TET administration decreased significantly faster than that in the adult.     

Effects of ethanol and sherry on the performance of a conditioned response in the rat

The effect of beverages containing ethanol was studied in male adult (Wistar derived) rats subjected to avoidance learning in a shuttle-box. Five sessions, each of 50 trials were held every 24 hr for 5 days. The following groups of rats drank ad lib during the 3 days prior to the first avoidance session and throughout the test period: (1) A control group which drank $\text{1}\text{3}$ isocaloric (related to alcoholic beverages) glucose in tap water. The animals drank about 3 volumes glucose related to one volume of alcoholic beverages. (2) Ethanol (17% v/v plus 2.0% glucose). (3) Sweet sherry (17% ethanol v/v plus 2.0% reducing sugars). (4) Artificial sherry made by mixing the volatile components (methanol, acetaldehyde, ethanol, n-propanol, ethylacetate, iso-butanol and iso-amylic alcohol) of sherry in water plus 2.0% glucose. (5) Artificial sherry without ethanol. (6) A control group which drank only water. No statistically significant difference was observed between the control groups on the avoidance learning task. Ethanol, sherry and artificial sherry significantly increased the performance level over that of the controls. The effect of ethanol was observed in the 5 sessions; that of sherry and artificial sherry after the third session. This difference is attributed to the absence of volatile congeners in the ethanol solution. In rats drinking for 19 days prior to the first avoidance trial and throughout the test period, neither ethanol nor sherry improved the performance level. When naive rats with an initially low performance level drank ethanol from the end of the first session and up to the last session their performance level was significantly increased. This effect was not observed when the rats drank sherry. After having drunk ethanol for 24 hr, the individual progress of rats with a low performance level was significantly increased until the last session. However, after having drunk sherry, individual progress was significantly favored in the 2nd session only.     

Effect of repeated benzene inhalation exposures on benzene metabolism, binding to hemoglobin, and induction of micronuclei

Metabolism of benzene is thought to be necessary to produce the toxic effects, including carcinogenicity, associated with benzene exposure. To extrapolate from the results of rodent studies to potential health risks in man, one must know how benzene metabolism is affected by species, dose, dose rate, and repeated versus single exposures. The purpose of our studies was to determine the effect of repeated inhalation exposures on the metabolism of [14C]benzene by rodents. Benzene metabolism was assessed by characterizing and quantitating urinary metabolites, and by quantitating 14C bound to hemoglobin and micronuclei induction. F344/N rats and B6C3F1 mice were exposed, nose-only, to 600 ppm benzene or to air (control) for 6 hr/day, 5 days/week for 3 weeks. On the last day, both benzene-pretreated and control animals were exposed to 600 ppm, 14C-labeled benzene for 6 hr. Individual benzene metabolites in urine collected for 24 hr after the exposure were analyzed. There was a significant decrease in the respiratory rate of mice (but not rats) pretreated with benzene which resulted in lower levels of urinary [14C]benzene metabolites. The analyses indicated that the only effects of benzene pretreatment on the metabolite profile in rat or mouse urine were a slight shift from glucuronidation to sulfation in mice and a shift from sulfation to glucuronidation in rats. Benzene pretreatment also had no effect, in either species, on formation of [14C]benzene-derived hemoglobin adducts. Mice and rats had similar levels of hemoglobin adduct binding, despite the higher metabolism of benzene by mice. This indicates that hemoglobin adduct formation occurs with higher efficiency in rats. After 1 week of exposure to 600 ppm benzene, the frequency of micronucleated, polychromatic erythrocytes (PCEs) in mice was significantly increased. Exposure to the same level of benzene for an additional 2 weeks did not further increase the frequency of micronuclei in PCEs. These results indicate that repeated exposures to benzene, such as might be encountered by humans as a result of occupational or environmental exposures, are not likely to change or increase benzene metabolism.     

Subcellular distribution of mercury in the rat kidney cortex after exposure to mercuric chloride

The pharmacologic effects and plasma concentrations produced by the ip administration of high doses of thymidine were determined in CDF₁ mice. Within 15 min after the injection of thymidine at a dose of 4.075 g/kg (between LD0 and LD50), mean arterial blood pressure and heart rate fell precipitously and remained depressed for over 6 hr. During the experimental period, sedation and anuresis were also consistently observed in thymidine-treated mice. After a dose of 4.7 g/kg, millimolar plasma thymidine concentrations were maintained for 16 to 20 hr; by contrast, at a lower but nonlethal dose (3.8 g/kg), millimolar plasma thymidine concentrations were maintained for only 9 hr. It is suggested that sustained elevation of circulating thymidine in the range 1–10 mm for periods greater than $\text{1}\text{2}$ day may be associated with toxicity in mice.     

Biliary excretion of silver in the rat, rabbit, and dog.

The fecal elimination of silver is more important than urinary elimination. Within 4 days after iv administration of silver to the rat (0.1 mg/kg), 70% is excreted into the feces and less than 1% into the urine. The disappearance of ¹¹⁰Ag from the plasma and its excretion into the bile were measured for 2 hr after the iv administration of 0.01, 0.03, 0.1, and 0.3 mg/kg of silver to rats. The concentration of silver in the bile was 16–20 times higher than that of the plasma. With the two lower doses of silver used, the overall plasma-to-bile gradient was due almost equally to the plasma-to-liver gradient and the liver-to-bile gradient and with the two higher doses of silver the liver-to-bile gradient became more important. Marked species variation in the biliary excretion of silver was observed. Rabbits excreted silver at a rate about $\text{1}\text{10}$, and dogs excreted silver at a rate about $\text{1}\text{100}$ of that observed in the rat. These results suggest that while species variation exist, biliary excretion is an important route for the elimination of silver.     

Inhibition of water intake by ouabain administration in sheep

Intracarotid infusion of ouabain (1280 ng/min) over $\text{4}\text{1}\text{2}\text{hr}$ virtually abolished water intake of sheep in response to intracarotid infusion of either angiotensin II (800 ng/min) or 4 M NaCl (1.6 ml/min for 20 min). Ouabain treatment did not affect mean arterial pressure either before or during infusion of angiotensin. Neither ouabain nor angiotensin administration affected plasma [Na] or [K] or CSF [K]. During ouabain, but not during control infusion, angiotensin administration significantly decreased CSF [Na]. Ouabain administration also decreased water intake after $\text{23}\text{1}\text{2}\text{or}\text{48}\text{hr}$ water deprivation. In the $\text{23}\text{1}\text{2}\text{hr}$ deprivation experiments, food was made available immediately prior to water presentation and the ingestion of food appeared to ameliorate the reduction in water intake. Food intake itself, was decreased in some animals, during ouabain treatment. Ouabain infused at 960 ng/min resulted in significant, but smaller, reductions in water intake induced by angiotensin, 4 M NaCl, and 48 hr water deprivation. It was concluded that ouabain treatment affected water intake by influence on Na transport either in the thirst receptors or at some other level in the neural system between receptor and effector.     

Drug interactions with misonidazole: Effects of dexamethasone and its derivatives on the pharmacokinetics and toxicity of misonidazole in mice

Misonidazole [1-(2-nitroimidazol-1-yl)-3-methoxypropan-2-ol; Ro 07-0582] selectively sensitizes hypoxic cells to radiation and is undergoing clinical trial in the radiation treatment of solid tumours. It has been suggested that the glucocorticoid hormone dexamethasone may reduce the incidence of neurotoxicity, the dose-limiting side effect of misonidazole in man. Here it is shown that the absorption and elimination of misonidazole (1 $\text{g}\text{kg}$ i.p.) in C3H mice are unaffected by pretreatment (i.p. for 5 days) with dexamethasone (10$\text{mg}\text{kg}$/day), dexamethasone acetate (10 $\text{mg}\text{kg}\text{day}$) and dexamethasone phosphate (0.5, 10, 25 and lOO $\text{mg}\text{kg}\text{day}$). The apparent half-life of misonidazole in blood and area under the curve (AUC) of misonidazole concentration × time were unaltered. Likewise O-demethylation was unaffected. In contrast, phenobarbitone pretreatment (80 $\text{mg}\text{kg}\text{day}$) increased misonidazole clearance through induction of demethylation. Dexamethasone phosphate pretreatment increased pentobarbitone sleeping-time and slightly decreased liver weight, whereas phenobarbitone did the opposite. Dexamethasone phosphate (25 $\text{mg}\text{kg}$) given as an i.v. bolus injection immediately before misonidazole also had no effect on the systemic pharmacokinetics of misonidazole. Broadly, pretreatment with dexamethasone derivatives had little effect on brain misonidazole and desmethylmisonidazole. But after 100 $\text{mg}\text{kg}\text{day}$ dexamethasone phosphate the 6 hr misonidazole concentration was reduced 36 per cent. Simultaneous dexamethasone phosphate (25 $\text{mg}\text{kg}$) reduced the concentration at 1 hr by 15 per cent and the brain AUC_(0–6hr) by 14 per cent. Dexamethasone phosphate pretreatment reduced the acute LD₅₀ for misonidazole by up to 19 per cent whereas phenobarbitone increased it by 16 per cent. Simultaneous dexamethasone phosphate had no effect. The drug had little effect on misonidazole-induced hypothermia. The significance of these findings for the putative role of dexamethasone in the protection of misonidazole neurotoxicity is discussed.     

Acute and chronic dose/response effect of benzene inhalation on the peripheral blood,bone marrow,and spleen cells of CD-1 male mice

Inhaled benzene hematotoxicity to recognize stem cell progeny was studied in male CD-1 mice exposed for 6 hr/day × 5 days to one of the following mean benzene concentrations: 1.1, 9.9, 103, 306, 603, 1276, 2416, and 4862 ppm. Additional groups of mice were exposed for 6 hr/day × 5 days/week × 10 weeks to 9.6 ppm, or 6 hr/day × 5 days/week × 26 weeks to 302 ppm. Following the 5-day exposures, granulocytopenia and lymphocytopenia were observed at levels ≥ 103 ppm with no change in WBC differential. RBC counts were depressed only at the two highest exposure levels while hematocrits were variably affected and showed no clear dose/response effect. Marrow and splenic cellularities were reduced at all levels ≥ 103 ppm. Marrow lymphocytes, splenic lymphocytes, and marrow granulocytes were reduced in accordance with the reduction in total cellularity, however, splenic granulocytes and spleen weights were depressed at almost all exposure levels. Nucleated RBCs in the marrow and spleen were depressed at almost all levels ≥ 103 ppm. Exposure for 50 days to 9.6 ppm benzene, a total dose equivalent to that delivered over 5 days at 103 ppm, induced no detectable changes in the peripheral blood or bone marrow, however, increases in splenic weight and cellularity were observed. Twenty-six weeks of exposure to 302 ppm benzene resulted in lymphocytopenia and anemia. Marrow cellularity was reduced to 32% of control and was due primarily to a reduction in lymphocytes and granulocytes. Spleen cellularity and weight were reduced to 17 and 67% of control, respectively. Decreased spleen cellularity was due primarily to a reduction in lymphocytes to 5% of control. These extended exposures to 302 ppm benzene resulted in atypical cell morphology in the peripheral blood, bone marrow, and spleen.     

Influences of gender,development, pregnancy and ethanol consumption on the hematotoxicity of inhaled 10 ppm benzene

 The hematotoxic effects of benzene in both humans and animals are well documented. Current estimates concerning the risks associated with benzene exposure are usually based on adult, male cohort studies; however, there are indications that females may respond differently than males to benzene and that fetuses may respond differently than adults. Another factor to be considered in risk estimates is the impact of personal habits. In experimental animals, ethanol consumption is known to increase the hematotoxicity of benzene; therefore, alcohol consumption may also alter the potential risk of individuals exposed to benzene. To address some of the factors that may confound risk estimates for benzene exposure, a series of experiments were performed. Age-matched male as well as pregnant and virgin female Swiss Webster mice were exposed to 10 ppm benzene for 6 h a day over 10 consecutive days (days 6 through 15 of gestation for the pregnant females). Half of the animals also received 5% ethanol in the drinking water during this period. On day 11, bone marrow cells from the adults and liver cells from the fetuses were assayed for the numbers of erythroid colony-forming units (CFU-e). CFU-e assays were also performed on bone marrow cells isolated from 6-week postpartum dams exposed during gestation and from in utero-exposed 6-week old males and females. Gender differences were clearly observed in the responses to the various exposure protocols. Depressions in CFU-e numbers were only seen in male mice while elevations in CFU-e numbers were only seen in female mice. Male mice exposed as adults for 10 days to benzene (B), ethanol (E) or benzene+ethanol (B+E) exhibited depressed CFU-e levels as did male fetal mice exposed to B in utero. In addition, adult male mice which had been exposed in utero to either B or to E individually displayed depressed CFU-e levels. In contrast, none of the groups of female mice exhibited any depressions in CFU-e numbers after any of the exposures. Elevations in CFU-e numbers were observed among pregnant females exposed to E and among adult females exposed to B+E in utero. In summary, a majority (6/9) of the exposure protocols produced depressions in the CFU-e numbers of male mice, whereas a majority (7/9) of the exposure protocols produced no changes in the CFU-e numbers of female mice. Those changes that were observed in females consisted of elevations of CFU-e numbers. These results suggest that the male erythron is more susceptible than the female erythron to the hematotoxicants benzene and ethanol, regardless of whether exposures occur in utero or during adulthood. Received: 21 February 1995 / Accepted: 14 May 1995     

Individualizing theophylline dosage: Evaluation of a single-point maintenance dose prediction method

Summary A dosage prediction method to estimate theophylline clearance and dose requirement was evaluated in 22 outpatients with partly reversible obstructive airways disease. The steady state theophylline dose required to achieve a target concentration (Css) was predicted using a single serum theophylline determination 8 h after a single oral test dose. In 17 nonsmoking patients a mean absolute deviation of 8.2% (range 0.0–21.7%) between predicted and observed Css was found, and in 5 smoking patients the mean deviation was 34.0% (range 2.2–53.8%). In 17 healthy smokers the single-point method was found to predict theophylline clearance at a sampling time of 8 h with a prediction error of 11.3 (range 0.8–25.3%) compared to the clearance determination using the area under the curve. In addition, a numerical simulation program to assess the influence of absorption, elimination and sampling time on predictive accuracy showed that the method could be successfully applied to a patient population with elimination rate constants between 0.07 1/h and 0.25 1/h, allowing a mean prediction error of 15%.     

The lack of effects of pretreatment with phenobarbital and chlorpromazine on the acute toxicity of benzene in rats

Female CD rats were injected ip daily for 3 days with either phenobarbital (75 mg/kg) or chlorpromazine (15 mg/kg). On the fourth morning the animals were either subjected to a 4-hr inhalation exposure of benzene or given an ip injection of 50% ($\text{v}\text{v}$) of benzene and mineral oil. Animals were injected with doses of 1, 2, 3 and 4 g benzene/kg body weight. In the inhalation studies, animals were exposed to 6 levels of benzene ranging from 11,500 to 15,500 ppm. The LD50 for animals injected with benzene and the LC50 for animals inhaling benzene were calculated for control groups and those pretreated with either phenobarbital or chlorpromazine. Neither the LD50 or the LC50 were affected by any of the treatment protocols. In order to determine that the pretreatment was stimulating benzene metabolism, a method for measuring benzene metabolism has been developed using [¹⁴C]benzene. These studies have shown that phenobarbital and 3-MC do induce benzene metabolism in the liver, that chlorpromazine slightly induces benzene metabolism in the lung, and that pretreatment by these compounds does not affect the acute inhalation toxicity or the ip toxicity of benzene.     

Distribution and excretion of 2,3,7,8-tetrachlorodibenzofuran in C57BL/6J and DBA/2J mice

The distribution and excretion of the toxic pollutant, 2,3,7,8-tetrachlorodibenzofuran (TCDF), was studied in male C57BL/6J and DBA/2J mice (22–29 g). [¹⁴C]TCDF was administered iv at a dose of 0.1 μmmol/kg. The liver was the major site of TCDF accumulation, with more TCDF in the livers of C57BL/6J mice compared to DBA/2J mice. TCDF had a half-life of approximately 1.8 days in the livers of both strains. At 7 hr and 1 day, respectively, radioactivity was redistributed to adipose tissue of C57BL/6J mice and DBA/2J mice. The terminal $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of TCDF in adipose tissue of C57BL/6J mice was 1.1 days, whereas it was 6.8 days in DBA/2J mice; the sixfold longer half-life in DBA/2J mice may be related to the approximately 36% greater adipose tissue content of this strain which may sequester more TCDF. More than 80 and 55% of the dose was excreted in the feces of C57BL/6J and DBA/2J mice, respectively, within 10 days as polar metabolites. The whole body half-life of TCDF was 2 days in C57BL/6J and 4 days in DBA/2J mice. Thus, DBA/2J mice sequester more of the TCDF dose in adipose tissue, accounting for a relatively slower rate of clearance and lower concentrations of TCDF at the putative target site(s) for toxic action.     

Effects of castration and testosterone administration on rat liver alcohol dehydrogenase activity

The effects of castration and testosterone administration on the activity of liver alcohol dehydrogenase and on the rate of ethanol elimination were determined in male Sprague-Dawley rats. Castration increased liver alcohol dehydrogenase activity. The total liver activity in castrated animals was 2.37 ± 0.229 (S.E.) $\text{mmoles}\text{hr}$ as compared with a value of 1.39 ± 0.125 $\text{mmoles}\text{hr}$ in sham-operated controls (P < 0.01). Testosterone administration partially suppressed the enhanced activity of liver alcohol dehydrogenase produced by castration. By contrast, in control animals testosterone administration resulted in a small paradoxical increase in liver alcohol dehydrogenase. The increase in the enzyme activity in castrated animals was associated with a parallel increase in the rate of ethanol elimination. Castrated and control animals showed decreases in free cytosolic and mitochondrial NAD⁺/NADH ratios after ethanol administration. These observations suggest that testosterone (and probably other as yet unknown factors modified by castration) affects liver alcohol dehydrogenase activity, and that the total enzyme activity can be a principal limiting factor in ethanol elimination.     

Synthesis of cholinesterase following poisoning with irreversible anticholinesterases: effects of theophylline and N6,O2-dibutyryl adenosine 3',5'-monophosphate on synthesis and survival.

The half-time ($\text{t}\text{1}\text{2}$) for return of whole blood cholinesterase (ChE) activity in mice following poisoning with Soman and DFP is on the order of 30 hr; in rats, the $\text{t}\text{1}\text{2}$ for return of whole blood ChE is 32 hr for Soman and 106 hr for DFP. In fact, the recovery of ChE activity in other rat tissues (liver and brain) is also significantly (p < 0.001) slower after DFP poisoning than after Soman poisoning. It appears that DFP adversely affects the normal rate for synthesis of ChE in rats; DFP does not affect overall protein synthesis in the rat as measured by ¹⁴C-amino acid incorporation into protein. Pretreatment of mice with a combination of theophylline-DBcAMP before poisoning with Soman causes animals to be more sensitive to the poison. Treatment of mice and rats with theophylline-DBcAMP at 24, 29, and 45 hr after Soman poisoning produces a dramatic increase in whole blood ChE but not in brain ChE at 48 hr; this increase in enzyme activity is due to pseudo-ChE and not acetyl-ChE. Ethionine, injected 1 hr before the initial dose of theophylline-DBcAMP, completely abolished the enhanced ChE activity observed in whole blood. These results suggest that the enhanced ChE activity observed in blood is due to a stimulating effect of the drugs on de novo synthesis and/or a release of ChE by the liver.     

The influence of ethanol on the stem cell toxicity of benzene in mice

BDF1 mice were exposed to 100, 300, and 900 ppm benzene vapor, and the numbers of hematopoietic progenitor cells, early and late erythroid progenitors (BFU-E and CFU-E) and granuloid progenitors (CFU-C), were determined with and without additional exposure to ethanol (5, 10, 15 vol%) in the drinking water. The duration of benzene inhalation was up to 4 weeks, 6 hr per day, 5 days per week. It was shown that the number of CFU-E per femur was depressed in a dose-dependent manner by benzene alone and also by ethanol combined with a given benzene concentration. CFU-E showed rapid regeneration after the end of the exposure, but not BFU-E and CFU-C. Prolongation of the ethanol exposure after withdrawal of benzene had only a marginal effect on progenitor cell regeneration.     

The effects of organophosphate-induced cholinergic stimulation on the antibody response to sheep erythrocytes in inbred mice

In a previous study, we demonstrated that parathion suppressed both the primary IgM and IgG response to sheep erythrocytes (SRC) in inbred and outbred mice (G. P. Casale, S. D. Cohen, and R. A. DiCapua, 1982, Toxicologist2, 94). Suppression occurred after a dosage which produced cholinergic effects but was absent after a lower dosage which did not produce cholinergic signs. This information suggested that immunosuppression might be mediated indirectly as a result of toxic chemical stress. The present study evaluated the relationship between the anticholinesterase action of parathion, malathion, and dichlorvos (DDVP) and their effects on the primary humoral response to SRC. Male $\text{C57B1}\text{6}$ mice were given a single dose of parathion (16 mg/kg, po), malathion (720 mg/kg, po), or DDVP (120 mg/kg, po) 2 days after immunization with SRC. Two days later, tissues were removed for cholinesterase (CHE) assay and enumeration of splenic antibody-forming cells (PFC). All three compounds produced moderate to severe cholinergic poisoning. DDVP produced cholinergic signs beginning $\text{1}\text{2}$ hr after dosing and lasting $\text{1}\text{2}$ to 1 hr. This profile was associated with a rapid but transient inhibition of brain CHE activity. In contrast, malathion and parathion produced prolonged cholinergic poisoning (4 to 7 hr) and prolonged suppression of brain CHE activity. All three compounds suppressed the primary IgM response. However, when they were given as multiple lower doses, none of the compounds suppressed the primary IgG response. These latter treatments produced no cholinergic signs. The cholinomimetic agent, arecoline (65 mg/kg, ip) produced a short-lived cholinergic crisis but no IgM suppression. Sustained-release arecoline produced prolonged cholinergic poisoning (3 to 5 hr) and reduced the number of IgM PFC to 50% of control. These results demonstrated that organophosphate-induced immunosuppression was associated with severe cholinergic stimulation. The immunosuppression may result from direct action of acetylcholine upon the immune system or it may be secondary to the toxic chemical stress associated with cholinergic poisoning.