Effects of exposure to ozone on susceptibility to experimental tuberculosis

Exposure of mice to 1.96 $\text{mg}\text{m}{}^3$ ozone (O₃) 3 $\text{h}\text{day}$, 5 days/week, for up to 8 weeks beginning at 1 or 2 weeks after challenge with Mycobacterium tuberculosis R 1Rv resulted in significant enhancement of bacterial titers in the lungs at 5 through 8 weeks after challenge when compared to mice exposed to filtered air. Exposure to lower concentrations of O₃ did not produce any significant changes compared to controls.Exposure of guinea pigs to 2.9 $\text{mg}\text{m}{}^3$ O₃ for 3 h immediately after challenge with M. tuberculosis resulted in a suppression of the cutaneous delayed hypersensitivity response, without affecting the serum hemagglutination antibody titers. However, exposure of guinea pigs to 0.98 $\text{mg}\text{m}{}^3$ O³ 3 $\text{h}\text{day}$ for 5 days, initiated within 3 h after the infectious challenge, enhanced hemagglutination antibody titers initially, but the delayed hypersensitivity reaction did not differ from controls.     

Effect of exposure to nitrogen dioxide on t and b cells in mouse spleens

Effects of exposure to nitrogen dioxide (NO₂) on thymus-derived (T) and bursa-derived (B) cells were studied in albino mice. The mice were exposed continuously 24 $\text{h}\text{day}$ to 940 $\text{μg}\text{m}{}^3$ NO₂ and to 188 $\text{μg}\text{m}{}^3$ NO₂ with daily 3-h peaks 5 $\text{days}\text{week}$ of either 470, 940 or 1880 $\text{μg}\text{m}{}^3$ NO₂. After 1, 3, 6, 9 and 12 months of exposure, single-cell suspensions were prepared from spleen and incubated with phytohemagglutinin (PHA) or bacterial lipopolysaccharide (LPS). The PHA and LPS responses from mice exposed to NO₂ were generally depressed when compared with those in mice exposed for the same time periods to filtered air.     

The effect of bencyclane on the oxidative phosphorylation in isolated mitochondria of heart and liver

Our experiments were designed to localize the inhibitory influence of bencyclane² on the process of oxidative phosphorylation in isolated heart and liver mitochondria. The following results were obtained: (1) The state-3-respiration of rat liver and rabbit heart mitochondria was inhibited by bencyclane. This inhibition was dependent on the substrate used as energy donator, being much more pronounced with glutamate $\text{(}\text{ed}{}_{50}\text{= 3.17 × 10}{}^{\mathrm{?8}}\text{or}\text{1.85 × 10}{}^{\mathrm{?7}}\text{moles/mg}$ of protein, respectively) than with succinate $\text{(}\text{ed}{}_{50}\text{= 3.4 × 10}{}^{\mathrm{?7}}\text{or}\text{4.78 × 10}{}^{\mathrm{?7}}\text{moles/mg}$ of protein, respectively). Since the 2,4-dinitrophenol stimulated respiration was equally inhibited, and glutamate transfer through the mitochondrial membrane not influenced, we assume the NADH-coenzyme-Q-reductase to be the site of interaction at the molecular level. (2) Bencyclane stimulates the state-4-respiration of isolated mitochondria with $\text{concentrations}\text{\$}\text{?}\text{= 10}{}^{\mathrm{?5}}\text{M}$. This effect depends on the molar bencyclane concentration of the incubation medium, and is not abolished by the addition of atractyloside, oligomycin or ruthenium red. Therefore, it is suggested that uncoupling of oxidative phosphorylation is the reason for this bencyclane effect. Theoretically, both of the described effects result in a reduction of the amount of ATP in the living cell. Possible consequences on myocardial function and the cardiovascular system are discussed in terms of previously published data in this field.     

Mechanisms by which quipazine,a putative serotonin receptor agonist,alters brain 5-hydroxyindole metabolism

Quipazine (2-[1-piperazinyl] quinoline maleate) was shown to increase serotonin and decrease 5-hydroxyindoleacetic acid concentrations in whole brain, several brain regions, and the spinal cord of rats 1 hr after its administration (10 mg/kg, i.p.). In animals with transected spinal cords, quipazine induced stronger activation of extensor reflexes than 5-hydroxytryptophan, chlorimipramine, or Lilly 110140. This response could be blocked by methiothepin. In slices of rat cerebral cortex, quipazine inhibited the uptakes of [³H]-serotonin (EC₅₀ = 10^?6 M) and [³H]-norepinephrine ($\text{EC}{}_{50}\text{= 2 × 10}{}^{\mathrm{?6}}\text{m}$); it was equipotent with Lilly 110140 in inhibiting serotonin uptake, but less potent than chlorimipramine ($\text{EC}{}_{50}\text{= 10}{}^{\mathrm{?7}}\text{m}$). Quipazine administration to rats did not inhibit monoamine oxidase activity, and actually elevated brain tryptophan levels. These observations suggest that the effects of quipazine on brain serotonin and 5-hydroxyindoleacetic acid concentrations could have been caused by direct activation of central serotonin receptors (which would secondarily decrease impulse flow along serotonergic neurones), or by the inhibition of serotonin reuptake, or by both mechanisms.     

Effect of polychlorinated biphenyls on the immune responses of rhesus monkeys and mice.

The relationship between lipid peroxidation, glutathione (GSH) content, and CCl₄-induced toxicity was investigated in rat hepatocytes isolated by a collagenase-perfusion technique. Two chemical initiators of lipid peroxidation, ferric ions complexed with adenosine diphosphate ($\text{ADP}\text{Fe}{}^{\mathrm{3+}}$) and diethyl maleate, were studied for comparison. CCl₄ caused a reduction of intracellular K⁺ and release of alanine aminotransferase (ALT) into the medium, but no evidence of lipid peroxidation, as measured by the absorbance of thiobarbituric acid (TBA)-reacting materials and lipid-extract diene conjugation. $\text{ADP}\text{Fe}{}^{\mathrm{3+}}$ caused lipid peroxidation, but only a small loss of K⁺. Diethyl maleate caused a greater amount of lipid peroxidation and cell damage than did $\text{ADP}\text{Fe}{}^{\mathrm{3+}}$. Neither response appeared to be related to the GSH content, which was reduced by diethyl maleate, but not by $\text{ADP}\text{Fe}{}^{\mathrm{3+}}$, and by CCl₄ only at the highest dose. The results suggest that lipid peroxidation is not a requisite step in CCl₄-induced toxicity in isolated hepatocytes.     

Kinetic studies on the deethylation of ethoxybenzamide: A comparative study with isolated hepatocytes and liver microsomes of rat

Kinetic parameters (K_m and V_max) of ethoxybenzamide deethylation in isolated rat hepatocytes and liver microsomes were compared. Adjustment of cofactors in microsomal deethylation, such as NADPH and Mg²⁺, to give optimum conditions, and appropriate correction of the apparent kinetic parameters for nonspecific binding and microsomal yield resulted in good agreement among the kinetic parameters of isolated hepatocytes [$\text{V}{}_{\mathrm{<mtext>max</mtext>}}\text{= 0.0863 μmole · min}{}^{\mathrm{?1}}\text{· (g liver)}{}^{\mathrm{?1}}$ and K_m = 0.459 mM] and microsomes [V_max = 0.124 μmoles · min^?1 · (gliver)^?1 and K_m = 0.378 mM].     

Effect of urban ozone levels on laboratory-induced respiratory infections

The effect of the time of exposure to an aerosol of viable microorganisms on the incidence of respiratory infections associated with a 3 h exposure to ozone (O₃) was studied. The 157 and 196 $\text{μg}\text{m}{}^3$ (0.08–0.1 ppm) levels of O₃ used occur regularly in some urban communities. The studies reported here show that the susceptibility of mice to a laboratory-induced infection can be maximally enhanced if the infectious challenge is concurrent with the exposure to O₃.     

Adenosine receptor interactions and anxiolytics

$\text{[}{}^3\text{H}\text{]-N}{}^6\text{-}\text{cyclohexyladenosine}$ and [³H]-1,3-diethyl-8-phenylxanthine label the A₁ subtype of adenosine receptor in brain membranes. The affinities of methylxanthines in competing for A₁ adenosine receptors parallel their potencies as locomotor stimulants. The adenosine agonist N⁶-(-phenylisopropyl) adenosine is a potent locomotor depressant. Both diazepam and $\text{N}{}^6\text{-(}\text{l}\text{-}\text{phenylisopropyl}\text{)}\text{adenosine}$ cause locomotor stimulation in a narrow range of subdepressant doses. Combined stimulant doses of the two agents depress motor activity, as do larger doses of either one, given separately.Evidence supporting and against the hypothesis that some of the actions of benzodiazepines are mediated via the adenosine system is reviewed. A number of compounds interact with both systems, probably because of physico-chemical similarities between adenosine and diazepam. It is concluded that of the four classic actions of benzodiazepines, the sedative and muscle relaxant (but not anxiolytic or anticonvulsant) actions could possibly be mediated by adenosine.     

Determination of extraction constant,true partition coefficient and formation constant of ion-pair complexes of quaternary ammonium salts,tetrabutylammonium bromide and isopropamide iodide.with some organic anions by a solvent extraction technique

A new method of determining the extraction constant (K_e, the true partition coefficient (TPC) and the formation constant (K_f) of ion-pairs, was developed by the solvent extraction technique. K_e and TPC were estimated from the reciprocals of the intercept and the slope of the regression line obtained by plotting

$\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{APC ? dA}\text{vs}\text{B}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{dA}\text{APC ? dA}\text{+}\text{A}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{+}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}$

in the following equation.

$\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{APC ? dA}\text{=}\text{1}\text{K}{}_{\mathrm{e}}\text{+}\text{B}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{dA}\text{APC ? dA}\text{+}\text{A}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{+}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{x}\text{1}\text{TPC}$

where [A^T_W] and [B^T_W] are the total concentrations of the cationic compound A and that of the anionic compound B in the aqueous phase respectively, APC is the apparent partition coefficient of A, dA is the partition coefficient of cation A⁺. K_f, which is expressed by K_e/TPC, was then calculated. These constants were determined for the ion-pair extraction of tetrabutylammonium bromide and isopropamide iodide with 4 organic anions, i.e. benzoic acid, p-toluenesulfonic acid, salicylic acid and taurodeoxycholic acid. This new method might be applicable to other ion-pairs without further assumptions except that the molar ratio of the ion-pair formation be 1 : 1.     

The effects of cadmium, manganese and aluminium on sodium-potassium-activated and magnesium-activated adenosine triphosphatase activity and choline uptake in rat brain synaptosomes

The effects of Cd²⁺, Mn²⁺ and Al³⁺ on rat brain synaptosomal sodium-potassium-activated and magnesium-activated adenosine triphosphatase (Na-K-ATPase and Mg-ATPase) activity and choline uptake were studied. All three types of metal ions inhibited Na-K-ATPase activity more markedly than Mg-ATPase activity. The rank order of inhibition of Na-K-ATPase was: $\text{Cd}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 5.4 μ}\text{M}\text{) >}\text{Mn}{}_{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 955 μ}\text{m}\text{) >}\text{Al}{}^{\mathrm{3+}}\text{(}\text{ic}{}_{50}\text{= 8.3}\text{mM}$). The rank order of inhibition of Mg- was:$\text{Cd}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 316 μ}\text{M}\text{>}\text{Mn}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 5.5}\text{mM}\text{>}\text{Al}{}^{\mathrm{3+}}\text{(}\text{ic}{}_{50}\text{= 21.9}\text{mM}\text{).}\text{Al}{}^{\mathrm{3+}}$ was most potent in inhibiting synaptosomal choline uptake ($\text{ic}{}_{50}\text{= 24μ}\text{M}$ in the absence of Ca²⁺ and 123 μ.M in the presence of 1 mM Ca²⁺). $\text{Cd}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 363 μ}\text{M}\text{)}$ was a more effective inhibitor of choline uptake than $\text{Mn}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 1.2?1.5}\text{mM}\text{)}$ . The presence of 1 mM Ca²⁺ did not alter choline uptake, nor did it antagonize the inhibitory actions of the three metals. Our observations that Cd²⁺ and Al³⁺ inhibited synaptosomal choline uptake, but did not show parallel inhibitory effects on Na-K-ATPase activity directly contradicts the ionic gradient hypothesis. These results are also discussed in relation to the in vivo neurotoxicity of cadmium, manganese and aluminium.     

Kinetic studies on the metabolism of ethylmorphine by isolated hepatocytes from adult rats

Hepatocytes of adult rats were isolated by infusion of a hyaluronidase collagenase mixture. High yields of cells excluding trypan blue were obtained. These cells, in Hank's buffer containing rat serum and 0.1% glucose, $\text{N-}\text{demethylate}\text{[}{}^3\text{H-CH}{}_3\text{-N]}$ethylmorphine. The formaldehyde initially formed is further metabolized to tritiated water. Fifteen per cent of the original metabolic activity was observed after 21 hr at 37° in 5% CO₂-air, and cumulative metabolism is linear for up to 90 min under these conditions. The K_m for the N-demethylation of [³H-CH₃-N]ethylmorphine is 50 μM, 20 per cent of the value observed for this reaction by musomal preparations. An active transport of the substrate into the cell is postulated to account for this difference.     

Mechanisms for the biodegradation of organic mercury compounds: the action of ascorbate and of soluble proteins.

Organic mercury compounds are to varying extents degraded by ascorbate and by soluble proteins. Phenyl-, methyl-, and methoxyethyl mercury are attacked by ascorbate, provided that the solution has been exposed to air in the presence of Cu²⁺, although the reaction can subsequently proceed in the absence of air. Mercury vapour (Hg⁰) and inorganic mercury (Hg²⁺) are released, and the $\text{Hg}{}^0\text{Hg}{}^{\mathrm{2+}}$ ratio varies with the three compounds, being high with methoxyethyl-mercury and very low with methylmercury. The $\text{Hg}{}^0\text{Hg}{}^{\mathrm{2+}}$ ratio is much reduced in the presence of cysteine. It is suggested that the ascorbate free radical is responsible for the reaction. γ-Globulin can degrade phenyl-mercury, but not methyl- and methoxyethylmercury, to yield Hg²⁺. The action is much stimulated by glutathione and dithiothreitol, and the evidence suggests that these act by reducing protein disulphide groups, and that the Hg²⁺ released remains attached to reactive protein thiol groups. Serum albumin appears to have a similar action. Most of the activity of the soluble fraction of a rat liver homogenate can be accounted for by the presence of thiol-activated proteins.     

The role of lipid,free radical initiator,and oxygen on the kinetics of lipid peroxidation

The relationship between the concentration of unsaturated lipid, free radical initiator, and oxygen concentration on the kinetics of lipid peroxidation was determined. The rate of lipid peroxidation was studied with the thiobarbituric acid (TBA), diene conjugation (DC), and ferrithiocyanate (Fe-SCN) methods. The rate of peroxidation was half-order with respect to unsaturated lipid, initiator, and oxygen. The half-order relationship could be expressed as: $\text{rate}\text{= (}\text{fk}{}_1\text{k}{}_2\text{k}{}_3\text{k}{}_6{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(}\text{azobisisobutyronitrile}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$$\text{(}\text{RH}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(}\text{O}{}_2\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. The half-order relationship was found with linoleic (18:2), linolenic (18:3), and arachidonic (20:4) acids. A linear relationship existed between the logarithm of unsaturation and the rate of peroxidation. No peroxidation of linolenic acid was indicated when the DC method was employed, but was when the TBA and Fe-SCN methods were used.     

Effect of oil of nutmeg on the fertility and induction of meiotic chromosome rearrangements in mice and their first generation

The dose-dependent effects of oil of nutmeg on the fertility and induction of chromosomal translocations in treated mice and their F₁ males were examined. C3H male mice were treated with oil of nutmeg for 8 successive weeks at 60, 80, 100 and 400 $\text{mg}\text{kg}$ body weight. The greatest reduction of fertility occurred in the group treated with 400 $\text{mg}\text{kg}$; chromosomal translocation in directly treated animals was not found. The chromosomal translocations in F₁ males, derived from males treated with oil of nutmeg occurred at dose levels of 60, 80 and 100 $\text{mg}\text{kg}$.     

Similar activities of nerve growth factor and its homologue proinsulin in intracellular hydrogen peroxide production and metabolism in adipocytes: Transmembrane signalling relative to insulin-mimicking cellular effects

Generation of hydrogen peroxide in adipocyte plasma membrane and its intracellular metabolism and regulatory role have been shown by Mukherjee and co-workers to be a major effector system for insulin [Fedn Proc.35, 1694 (1976); Archs Biochem. Biophys.184, 69 (1977); Biochem. Pharmac.27, 2589 (1978); Fedn Proc.37, 1689 (1978); and Biochem. Pharmac.29, 1239 (1980)]. The possible involvement of this mechanism in the action of structurally similar polypeptides having some insulin-like metabolic effects was investigated. The β-subunit of nerve growth factor (2.5 S NGF, mol. wt 13,500) which has a striking structural homology with proinsulin and has been reported to exert certain insulin-like metabolic effects in its own target tissues (e.g. growing neurites and sympathetic ganglia), and the insulin-derived polypeptides, desalanine-insulin and desoctapeptide-insulin, as well as proinsulin, were examined for their effects on rat adipocytes, employing the technique of formate oxidation. Both NGF and proinsulin caused increased [¹⁴C]formate oxidation, showing similar intrinsic activities, up to a maximum of 140–160% of the basal rate; insulin increased the rate to 190–210% of the basal rate. The relative potencies of the hormones toward H₂O₂ formation and stimulation of the pentose phosphate pathway activity were: insulin $\text{(}\text{EC}{}_{50}\text{: 2.5 × 10}{}^{\mathrm{?11}}\text{M}\text{)}$, desalanine-insulin $\text{(}\text{EC}{}_{50}\text{: 2.5 × 10}{}^{\mathrm{?10}}\text{M}\text{)}$ , proinsulin $\text{(}\text{EC}{}_{50}\text{: 8 × 10}{}^{\mathrm{?9}}\text{M}\text{)}$, and NGF $\text{(}\text{EC}{}_{50}\text{: 10}{}^{\mathrm{?9}}\text{M}\text{)}$. The biologically inactive derivative, desoctapeptide-insulin, did not stimulate glucose oxidation, although it caused a small increase in formate oxidation, with an $\text{EC}{}_{50}\text{of}\text{5 × 10}{}^{\mathrm{?7}}\text{M}$, indicating a suboptimal level of H₂O₂ formation in the elevation of the hexose monophosphate shunt activity. 3-Amino-1,2,4,-triazole (50 mM), which irreversibly decomposes the peroxidatic compound II of the catalase: H₂O₂ complex, inhibited formate oxidation to a greater extent in the hormone-treated cells than in the control cells, whereas sodium azide, an inhibitor of the hemoprotein, catalase, completely inhibited it. The abilities of the polypeptides to stimulate H₂O₂ formation correlated with their abilities to promote lipogenesis from [U-¹⁴C]-D-glucose, as expected of insulin. The cellular GSH/GSSG ratio increased concomitantly with the stimulation of glucose oxidation via the shunt, indicating a tight coupling between these processes. The results confirm that the hydrogen peroxide production is a common basis of the metabolic actions of growth-promoting polypeptide hormones or mitogens beyond their respective receptors.     

Effects of catecholamine releasing agents on synaptosomal dopamine biosynthesis: Multiple pools of dopamine or multiple forms of tyrosine hydroxylase?

The effects of agents, which are known to induce release of catecholamines from synaptosomes, were assessed on the synthesis of dopamine from tyrosine, as reflected in the evolution of ¹⁴CO₂ from L-[1-¹⁴C]-tyrosine, in intact rat striatal synaptosomes. At a time when release had occured, whereas reserpine inhibited the synthesis of dopamine from tyrosine, with an ED₅₀ of $\text{1 × 10}{}^{\mathrm{?8}}\text{M}$, tyramine (ED₅₀ of $\text{1 × 10}{}^{\mathrm{?5}}\text{M}$) and (+)-amphetamine (ED₅₀ of $\text{1·4 × 10}{}^{\mathrm{?6}}\text{M}$) enhanced the rate of synthesis. The presence of nialamide (10^?4M) or pargyline (10^?3M) had no effect on synaptosomal dopamine synthesis in the absence or presence of amphetamine, tyramine, or reserpine. Neither reserpine, tyramine, nor amphetamine effected the activity of tyrosine hydroxylase or DOPA decarboxylase in the absence of synaptosomal structural integrity. Nor did these drugs effect the accumulation of [³H]-tyrosine into synaptosomes. The data are consistent with the existence of at least two pools of synaptosomal dopamine, one of which can interact with tyrosine hydroxylase. Two hours after pretreatment of rats with 5 mg/kg (+)-amphetamine, the level of synaptosomal dopamine biosynthesis was decreased by 39%. The rate of dopamine synthesis in synaptosomes from amphetamine-pretreated rats was assessed in the presence of reserpine and tyramine. The data are not consistent with alterations in pool size being the only mechanism affecting synaptosomal dopamine synthesis. A mechanism is discussed involving an equilibrium of tyrosine hydroxylase between active and inactive conformers in the presence of an inhibitory pool of dopamine.     

Inhalation studies on the biotransformation and elimination of [14C] trichlorofluoromethane and [14C] dichlorodifluoromethane in beagles

The possible biotransformation of trichlorofluoromethane (FC-11) and dichlorodifluoromethane (FC-12) was investigated in 4 male and 2 female adult Beagles after a short (6- to 20-min) inhalation. Dogs were anesthetized with ketamine and succinylcholine, intubated, and ventilated artificially. Trichlorofluoromethane (1000–5000 ppm, $\text{v}\text{v}$) or dichlorodifluoromethane 38000–12,000 ppm, $\text{v}\text{v}$) containing up to 180μ Ci of $\text{[}{}^{14}\text{C}\text{]}\text{fluorocarbon}$ was delivered from 110-liter Teflon bags, and all exhalations were collected via a nonrebreathing valve in similar bags for 1 hr. Venous blood samples were withdrawn at appropriate times and assayed for fluorocarbon-associated radioactivity. Exhalation bags were assayed for $\text{[}{}^{14}\text{C}\text{]}\text{fluorocarbon}$ and ¹⁴CO₂. Urine was collected for up to 3 days and assayed for ${}^{14}\text{C}$ metabolites as nonvolatile radioactivity. In some experiments animals were sacrificed 24 hr after exposure and tissues were removed for determination of nonvolatile radioactivity. Essentially all of the administered (inhaled) fluorocarbon was recovered in the exhaled air within 1 hr. Only traces of radioactivity were found in urine or exhaled carbon dioxide. All tissues contained measurable concentrations of nonvolatile radioactivity 24 hr after exposure but together represented less than 1% of the administered dose. It is not possible to determine if these trace levels are associated with metabolites of the fluorocarbons or with the unavoidable radiolabeled impurities present in the administered gas mixture. Neither phenobarbital pretreatment (60 mg/day for 3 days) nor prolonged exposure (50–90 min) produced any alteration of these results. Thus, it can be concluded that FC-11 and FC-12 are relatively refractory to biotransformation after a short inhalation exposure and that they are rapidly exhaled in their unaltered chemical form.     

Concentrations of nitrate in normal human urine and the effect of nitrate ingestion

A method suitable for the analysis of nitrate in human urine was developed. Normal urinary concentrations of nitrate in urine of human volunteers in Dade County, Florida, where the drinking water contains negligible amounts of nitrate, averaged 47.6 ppm of $\text{NO}{}_3{}^{\mathrm{?}}$ (SD = 17.3). On a vegetable and preserved-meat-free diet, the nitrate concentration was reduced (10 to 30 ppm of $\text{NO}{}_3{}^{\mathrm{?}}$), but, on nitrate-supplemented drinking water, the urinary concentration rose to a range of 34–87 ppm of $\text{NO}{}_3{}^{\mathrm{?}}$. A high vegetable diet resulted in peak urinary nitrate concentrations of 270–425 ppm. These results indicated that nitrate in drinking water is a factor in determining urinary nitrate concentration, but that vegetable ingestion is of greater significance.     

Studies on the respiratory uptake and excretion and the skin absorption of methyl n-butyl ketone in humans and dogs

Methyl n-butyl ketone (MnBK) has produced peripheral neuropathy in experimental animals and is implicated in an occupationally produced neuropathy. Since occupational exposure to MnBK is by inhalation or skin contact, both the absorption and elimination of MnBK vapor and its absorption through skin were investigated. Studies were carried out first with male beagle dogs and subsequently with human volunteers. Humans exposed for 7.5 hours to 10 or 50 ppm or for 4 hr to 100 ppm of MnBK vapor absorbed between 75 and 92% of the inhaled vapor. Unchanged MnBK was not eliminated extensively in the postexposure breath or in urine. 2,5-Hexanedione, a metabolite of MnBK known to be neurotoxic in rats, was found in the serum of humans exposed to either 50 or 100 ppm of MnBK. The absorption and elimination of MnBK in dogs was similar to that observed in humans. The skin absorption of [1-¹⁴C]MnBK or a $\text{9}\text{1}$ ($\text{v}\text{v}$) mixture of methyl ethyl ketone $\text{(MEK)}\text{[1-}{}^{14}\text{C]MnBK}$ was determined by excretion analysis. Two volunteers exposed by skin contact to [1-¹⁴C]MnBK absorbed 4.8 μg min^?1 cm^?2 and 8.0 μg min^?1 cm^?2, respectively. Skin exposure to $\text{MEK}\text{[1-}{}^{14}\text{C]MnBK}$ resulted in the respective absorption of 4.2 and 5.6 μg min^?1 cm^?2 by two individuals. Two volunteers given an oral dose of [1-¹⁴C]MnBK (2 μCi; 0.1 mg/kg) excreted 49.9 and 29.0% of the dose, respectively, as respiratory ¹⁴CO₂ within 3 to 5 days and 27.6 and 25.0% of the dose, respectively, in urine within 8 days. Both [1-¹⁴C]MnBK and $\text{MEK}\text{[1-}{}^{14}\text{C]MnBK}$ were absorbed through the skin of dogs. These findings show that MnBK is readily absorbed by the lungs, the gastrointestinal tract, and through the skin, is not eliminated extensively unchanged in breath or urine, and is metabolized to CO₂ and 2,5-hexanedione. Radioactivity derived from [1-¹⁴C]MnBK was excreted slowly by man, suggesting that repeated daily exposure to high concentrations of MnBK may lead to a prolonged exposure to neurotoxic metabolites.