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.     

Excretion of THC and its metabolites in ewes' milk

After single iv injections of either 0.02 mg/kg or 1 mg/kg of $\text{[}{}^{14}\text{C}\text{]Δ}{}^9\text{-}\text{tetrahydrocannabinol}$, [¹⁴C]THC, to lactating ewes, radioactivity was detected in the milk at all subsequent time intervals tested (4–96 hr). Radioactivity was found in unchanged THC as well as in various unidentified metabolites. Only about 15% of the administered radioactivity was excreted by the ewes in the first 48 hr; most of this was in the urine and feces. Radioactivity appeared in the feces and urine of a lamb suckling milk from a ewe injected with [¹⁴C]THC, indicating transfer of THC and its metabolites via the milk. These results confirm previous literature reports indicating slow elimination of THC, and show that milk is an additional route of excretion.     

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.     

Depression of hepatic cytochrome P450 monooxygenases after chronic environmental tobacco smoke exposure of young ferrets

Six-week-old ferrets were exposed head-only to clean air or environmental tobacco smoke (ETS) for 2 h/day, 5 days a week for a total of 8 weeks. Exposure to ETS caused a significant reduction in the levels of hepatic microsomal cytochrome P450 and P450 reductase activity in both the male and female ferrets. The content of cytochrome b₅ and the activity of its reductase were significantly reduced in the hepatic microsomes of female ferrets. 7-Ethoxycoumarin O-deethylase activity and cytochrome P450 (CYP) 1A protein were markedly decreased in the hepatic microsomes of both the male and female ferrets after ETS exposure. In accord with the downregulation of P450, total metabolites formed from benzo[a]pyrene were significantly reduced in the liver homogenates of ETS-exposed animals. Similarly, sum total of free (+)-anti-benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide, glutathione conjugates and DNA-bound metabolites formed from precursor (−)-7R-trans-benzo[a]pyrene-7,8-dihydrodiol showed marked reduction in both the male and female ferrets after ETS exposure in a dose-response manner. This is the first report showing downregulation of hepatic P450 and accompanying benzo[a]pyrene metabolism after tobacco smoke exposure which apparently occurred after an initial upregulation of these parameters (Rasmussen et al. (1994) FASEB J. 8, A122).     

Tissue distribution of histamine in a mutant mouse deficient in mast cells: Clear evidence for the presence of non-mast-cell histamine

The contents of histamine in various tissues of mutant mice deficient in mast cells ($\text{W}\text{W}{}^{\mathrm{v}}$) and in congenic normal mice (+/+) were determined by high-performance liquid chromatography and were compared. In spite of the absence of mast cells in $\text{W}\text{W}{}^{\mathrm{v}}$ mice, the histamine content of their whole bodies was about 5–10% of that of +/+ mice. The skin, heart and lungs of $\text{W}\text{W}{}^{\mathrm{v}}$ mice contained negligible amounts of histamine (about 2% of that in +/+ mice), but the liver, kidneys and spleen contained appreciable histamine (8–15% of that in +/+ mice), and the brain and stomach contained much histamine (45 and 34%, respectively, of that in +/+ mice). These results indicate the presence of non-mast-cell histamine, especially in the brain and stomach, where it may play important physiological roles.     

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.     

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.     

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.     

Brain metabolite concentrations and redox states in rats fed diets containing 1,3-butanediol and ethanol

Both ethanol and its dimer 1,3-butanediol (BD) are substrates for alcohol dehydrogenase in liver and thus have many similar effects upon metabolite concentrations and redox states in that organ. Although the mechanism by which ethanol exerts its effects on the brain is not known, it must differ from that in liver since brain contains insignificant amounts of alcohol dehydrogenase. The effects of BD, which does not produce intoxication, and ethanol upon brain were compared in an attempt to determine which changes in metabolite content are related to depression of the CNS. Diets containing 47% of calories as ethanol, BD, or glucose were pair-fed to rats for 62 days. The brains were then removed and frozen with a new apparatus which prevents postmortem changes, and concentrations of metabolites were determined. Substitution of BD for glucose in the diet caused a decrease in the brain content of glucose, lactate and α-oxoglutarate and an increase in glutamate and citrate. Substitution of ethanol for glucose caused only a decrease in the brain content of glucose and an increase in citrate. The ethanol diet, as compared with the BD diet, caused an elevation of the brain content of glucose and a decrease in glutamate. Both BD and ethanol caused a decrease in the free cytoplasmic $\text{[}\text{NADP}{}^{\mathrm{+}}\text{]}\text{[}\text{NADPH}\text{]}$ ratio in brain without changing the $\text{[}\text{NAD}{}^{\mathrm{+}}\text{]}\text{[}\text{NADH}\text{]}$ of cytoplasm or mitochondria.Except for the differences in effect upon glucose and glutamate, BD and ethanol appear to act similarly on the metabolite content of rat brain. It is therefore concluded that the brain is resistant to changes of the measured metabolites during the process of chronic ethanol ingestion. It is further suggested that the small changes observed in the cytoplasmic $\text{[}\text{NADP}{}^{\mathrm{+}}\text{]}\text{[}\text{NADPH}\text{]}$ ratio after ethanol feeding are not related to the depression of CNS activity associated with ethanol ingestion since they also occur after feeding BD.     

Effect of diphenylhydantoin on the uptake and catabolism of l-[3H]norepinephrine in vitro in rat cerebral cortex tissue

The effect of diphenylhydantoin on the accumulation of [³H]norepinephrine in vitro was examined in brain slices prepared from rat cerebral cortex. High concentrations of diphenylhydantoin (10^?3 M) caused a significant reduction in the 5-min accumulation of [³H]norepinephrine. On the other hand, 10^?5–10^?4 M diphenylhydantoin facilitated the 20-min accumulation of [³H]norepinephrine. This facilitative action of diphenylhydantoin was (1) associated with a reduction in oxidative catabolism of [³H]norepinephrine and (2) abolished by the 2-hr pretreatment of rats with 100 mg/kg of nialamide (i.p.). The inhibitory action of diphenylhydantoin on the oxidative catabolism of [³H]norepinephrine was observed in both whole and lyzed crude synaptosomal preparations. When diphenylhydantoin and pargyline were compared, it was found that pargyline $\text{(}\text{id}{}_{50}\text{= 1.5 × 10}{}^{\mathrm{?6}}\text{M}\text{)}$ was 37 times more effective than diphenylhydantoin $\text{(}\text{id}{}_{50}\text{= 5.5 × 10}{}^{\mathrm{?5}}\text{M}\text{)}$ in inhibiting the oxidative deamination of [³H]norepinephrine. These results suggest that diphenylhydantoin alters norepinephrine metabolism in cerebral cortex slices by an inhibitory action on (1) monoamine oxidase activity and (2) the neuronal uptake system.     

Extrapineal amine N-acetylation in rat brain: Regional and subcellular distribution and enzyme kinetics

Analysis by thin-layer chromatography showed that $\text{[}{}^{14}\text{C}\text{]N-}\text{acetyltryptamine and}\text{[}{}^{14}\text{C}\text{]N-}\text{acetyl}\text{-β-}\text{phenylethylamine}$ are formed from the incubation of [¹⁴C]acetyl-CoA with tryptamine or β-phenylethylamine. respectively, in the presence of rat brain extracts. The specific activity of the N-acetyltransferase in fifteen discrete regions of rat CNS ranged from 1.64 ± 0.05 nmoles of product formed/mg of protein/hr in cerebellum to 0.57 ± 0.05 nmole in occipital cortex with tryptamine as substrate, and from 2.80 ± 0.30 nmoles in cerebellum to 0.91 ± 0.13 nmole in cervical cord with β- phenylethylamine as substrate. Comparison of the regional specific activities in the presence of the respective substrates yielded a correlation coefficient of 0.83 (P < 0.01). In cerebellum N-acetyltransferase activity appears exclusively in cytosol. At two stages of purification (i.e. after Bio-Gel fractionation as well as after ammonium sulfate precipitation), the enzyme exhibited biphasic kinetics with respect to acetyl-CoA in the presence of tryptamine or β-phenylelhylamine and with respect to either substrate in the presence of acetyl-CoA.     

Turnover of liver proteins in Phenoclor DP6-treated rats.

The effect of a diet containing Phenoclor DP6 on the average turnover of protein in subcellular fractions of the liver was studied in young rats. In experiment A, rats were given an intraperitoneal injection of $\text{[}{}^{14}\text{C}\text{]-}\text{guanidinolabeled}$ arginine, were then fed a diet containing 100 ppm of Phenoclor DP6 for 24 h, and then resumed a control diet. In experiment B rats were fed a DP6 diet for 4 days prior to receiving the isotope injection, and then resumed the DP6 diet for the entire experiment. Afterward, these rats were killed 1, 3, 5, and 8 days after pulse-labeling. Mitochondrial, microsomal, microsomal membrane, and ribosomal fractions were prepared from their livers, and these fractions were analyzed for acid-precipitable protein and radioactivity. Our results indicate no significant difference in the average rates of ${}^{14}\text{C}$ degradation between rats receiving a single DP6 dose and the control group. In rats ingesting a DP6 diet every day, the half-lives of total liver proteins were significantly shorter than in the control group. This difference is perhaps due to the rate of breakdown of the microsomal proteins. We found that in the microsomal fraction only the microsomal membrane proteins were affected by the DP6 treatment. Our results suggest that under our experimental conditions microsomal membrane protein metabolism (synthesis and breakdown) is enhanced by DP6 ingestion.     

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.     

Hydrocarbons and metabolites in english sole (Parophrys vetulus) exposed simultaneously to [3H]benzo[a]pyrene and [14C]naphthalene in oil-contaminated sediment

English sole (Parophrys vetulus) were exposed to $\text{[}{}^3\text{H]benzo}\text{[a]}\text{pyrene (B}\text{[a]}\text{P}\text{)}$ and [¹⁴C]naphthalene (NPH) in sediment containing 1% Prudhoe Bay crude oil (PBCO). Bioeoncentration values (pmoles of hydrocarbon equivalents in g of dry tissue/pmoles of hydrocarbon equivalents in g of sedimentassociated water (SAW)) for NPH were greater than corresponding values for B[a]P in tissues of fish exposed for 24 h. However, from 24 to 168 h of the exposure, a substamial decline (P < 0.05) in NPH-derived radioactivity and a significant (P < 0.05) increase in B[a]P-derived radioactivity occurred in most of the tissues examined. When fish were transferred for 24 h to sediment free of radioactivity and PBCO, the retention of B[a]P-derived radioactivity in the tissues of fish was considerably greater than that for NPH.Metabolites of B[a]P and NPH in sediment, SAW, liver and bile of fish were characterized by thinlayer chromatography (TLC). For liver, a two-dimensional TLC was devised to separate B[a]P and its metabolites from liver lipids. An important finding was that liver of English sole metabolized B[a]P to a far greater extent than NPH; at 24 h after the exposure, the ratio of concentrations of B[a]P to its metabolites was 1 to 49 whereas that for NPH was 6 to 1. Larger proportions of glucuronide conjugates than sulfate conjugates of both NPH and B[a]P were present in bile of English sole. Naphthalene was largely converted into a glucuronide conjugate of l,2-dihydro-l,2-dihydroxynaphthalene. A number of metabolites of B[a]P known to be toxic to mammals were detected in both liver and bile including 7,8-dihydro-7,8-dihydroxy B[a]P and its conjugates.These findings of extensive metabolism of B[a]P by fish liver very probably explain why B[a]P is usually not detected in liver of fish even when considerable concentrations of B[a]P are detected in the environment of the fish.     

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.     

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.     

The Ah regulatory gene product. Survey of nineteen polycyclic aromatic compounds' and fifteen benzo[a]pyrene metabolites' capacity to bind to the cytosolic receptor

The capacity of 19 polycyclic aromatic compounds and 15 benzo[a]pyrene metabolites to displace $\text{[1,6-}{}^3\text{H}\text{]2,3,7,8-}\text{tetrachlorodibenzo}\text{-p-}\text{dioxine}\text{([}{}^3\text{H]Tcdd}\text{)}$ from the mouse liver cytosolic Ah receptor was examined. We compared our data with various parameters taken from previously published results: the capacity of seven polycyclic hydrocarbons to induce aryl hydrocarbon hydroxylase (AHH) activity in human cell cultures, the capacity of 10 polycyclic hydrocarbons to induce azo dye N-demethylase activity in rat liver, the capacity of 6 polycyclic hydrocarbons to shorten zoxazolamine paralysis times in the intact rat, and the capacity of 15 benzo[a]pyrene metabolites to induce AHH activity in rat hepatoma H-4-II-E cultures. An excellent correlation is seen between the capacity to displace the radioligand from the Ah receptor and the capacity to induce these monooxygenase activities. Differences in the rate of cellular uptake and formation of alkali-extractable metabolites of dibenzo[a,h]anthracene, 3-methylcholanthrene, and benzo[a]anthracene in Hepa-1 mouse hepatoma cell cultures do not account for differences in the capacity of these three polycyclic hydrocarbons to displace [³H]TCDD from the Ah receptor.     

The inhibitory action of ketamine HC1 on [3H]5-hydroxytryptamine accumulation by rat brain synaptosomal-rich fractions: comparison with [3H]catecholamine and [3H]gamma-aminobutyric acid uptake.

Ketamine HO was incubated with synaptosomal-rich fractions prepared from rat cerebral cortex to evaluate the effect of this agent upon the synaptosomal accumulation of [³H]5-HT. Accumulation of [³H]5-HT was shown to be reduced by ketamine in a concentration-related fashion. This action of ketamine was also found in synaptosomal rich fractions prepared from hypothalamus, corpus striatum, medulla oblongata and midbrain. Accumulation studies carried-out in the presence of reserpine and pargyline indicated that ketamine reduced the accumulation of [³H]5-HT through a competitive action on the synaptosomal membrane high affinity transport system (neuronal reuptake system). The effect of ketamine on the high affinity transport of [³H]NE, [³H]DA and [³H]GABA was also examined. The order of inhibition of transport by ketamine was [³H]5-HT >$\text{[}{}^3\text{H}\text{]}\text{DA}\text{= [}{}^3\text{H}\text{]}\text{NE}\text{> [}{}^3\text{H}\text{]}\text{GABA}$. These results show that ketamine is a potent and preferential inhibitor of the 5-HT neuronal reuptake system. The possible role of this action of ketamine, in the post anaesthetic excitatory response seen following the administration of ketamine, is discussed.     

Studies of the metabolism of N-methyl containing anti-tumour agents: 14CO2 breath analysis after administration of 14C-labelled N-methyl drugs, formaldehyde and formate in mice

The ¹⁴CO₂; content of the breath was analysed after administration of the following N-¹⁴ CH₃ labelled drugs to mice: aminopyrine, hexamethylmelamine (HMM), pentamethylmelamine (PMM), procarbazine and caffeine. Except for aminopyrine, the ¹⁴CO₂; exhalation rate plots declined monophasically with half lives of 91 min ([¹⁴C]-HMM), 97 min ([¹⁴C]-PMM), 68 min ([¹⁴C]procarbazine) and 92 min ([¹⁴C]caffeine). The ¹⁴CO₂ exhalation rate peaked rapidly after aminopyrine administration and declined bi-phasically with an initial $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of 15 min and a terminal $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of 126 min. The ¹⁴CO₂; plots after both [¹⁴C]-HMM and [¹⁴C]aminopyrine were influenced by pre-treatment of mice with proadifen. Pretreatment with phenobarbitone shortened the $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of the ¹⁴CO₂ appearance rate after [¹⁴C]HMM by 24% but did not change the ¹⁴CO₂ curve after administration of [¹⁴C] aminopyrine. The ¹⁴CO₂ exhalation rate plots after administration of H¹⁴CHO and H¹⁴COOH were virtually identical with that obtained after [¹⁴C]aminopyrine and not influenced by either proadifen or phenobarbitone pretreatment. The ¹⁴CO₂ exhalation rate profile obtained on metabolism of [¹⁴C]aminopyrine in mice thus appears to be determined by the rate of the oxidation of formaldehyde or formate to CO₂. Only 24% of the label injected with the N-methyl moieties of [¹⁴C]HMM and 21% of the label in [¹⁴C]procarbazine were exhaled as ¹⁴CO₂, whereas 49% of the N-¹⁴CH₃ in [¹⁴C]aminopyrine were metabolized to ¹⁴CO₂. It remains to be determined whether this difference and the difference in the shapes of the ¹⁴CO₂ exhalation profiles obtained with the cytotoxic N-¹⁴CH₃ drugs as compared to [¹⁴C]aminopyrine, are related to the biochemical processes mediating their antineoplastic activity.     

Effects of egg and sperm maturation and spawning on the distribution and elimination of a polychlorinated biphenyl in rainbow trout (Salmo gairdneri).

Distribution and elimination of $\text{2,5,2′,5′-}\text{tetrachloro}\text{[}{}^{14}\text{C}\text{]}\text{biphenyl}$ (4-CB) were studied for 1 year after exposing female and male rainbow trout to the compound in water and then transferring the fish to a hatchery raceway. The fish were exposed in December, weights of the maturing eggs and sperm began to increase in June, and the fish began to spawn in October. From January through August elimination of 4-CB was slow with a $\text{t}\text{1}\text{2}$ for whole body elimination of 1.76 years in females and 1.43 years in males. However, during the spawning season whole body elimination was more rapid in both sexes; $\text{t}\text{1}\text{2}\text{= 0.52}\text{year}$ in females and 0.54 year in males. The increased elimination rate appeared primarily to be due to the voiding of 4-CB containing eggs and sperm as opposed to enhanced elimination of 4-CB from extragonadal tissues. Prior to the enhanced elimination there was a redistribution of 4-CB residues within the fish's body. This was characterized by a depletion of 4-CB from eyes and periorbital fat, followed later in time, by a reduction in 4-CB content of visceral fat. Temporally related to this was an accumulation of 4-CB residues in maturing eggs and sperm. Thus, redistribution of 4-CB occurred during spermatogenesis and vitellogenesis and preceded the enhanced elimination of 4-CB from the whole fish when the gametes were spent from the body. The overall significance of this study is that it underlines the enhancing effect of egg and sperm maturation and spawning on whole body elimination of polychlorinated biphenyls in fish.