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 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.     

Electrocortical changes induced by perfusion of catecholamines into the brainstem reticular formation

Various concentrations of noradrenaline and related catecolamines were perfused bilaterally into the pontine and mesencephalic reticular formation using push-pull cannulae. The initial effect of a 5-min perfusion of (-)-noradrenaline, (-)-adrenaline, (-)-phenylephrine or α-methyl noradrenaline, was to induce a two stage change in the electrocortical activity, that is, phasic followed by tonic desynchronisation. When high concentrations of these substances were used, a secondary sedative effect correlated with the appearance of slow wave (2–4 Hz) activity in the electrocorticogram was observed. In contrast, (-)-isoproterenol, even in high concentrations, did not produce secondary sedative effects.Using tritium labelled (±)-[7-³H]-noradrenaline in the 10^?6 to 10^?3m concentration range, it was established that the total amount of drug diffusing into the brain tissue was very low. The appearance of phasic electrocortical changes correlated with 0·4–25 ng noradrenaline (base) within the brain at the end of each cannula. Tonic electrocortical desynchronization which appeared when $\text{9 × 10}{}^{\mathrm{?5}}\text{m}\text{to}\text{7 × 10}{}^{\mathrm{?4}}\text{m}$ solutions were used, gave tissue levels of exogenous noradrenaline (base) of 6·5–103 ng. Secondary sedative effects were usually observed with tissue levels in excess of 98 ng at the end of each cannula.     

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.     

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.     

Biological fate of a representative lipophilic metal compound (ferrocene) deposited by inhalation in the respiratory tract of rats

Rats were exposed by the nose-only route to ferrocene vapor labeled with ${}^{59}\text{Fe}$ and tritium. Serial sacrifices were performed up to 117 days following exposure. Over 75% of the tritium label was excreted within the firt day but the ⁵⁹Fe label largely remained in the bronchopulmonary and nasopharyngeal regions over the duration of the experiment.     

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.     

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.     

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.     

A fluorescent analogue of methotrexate as a probe for folate antagonist molecular receptors

A dansyl-l-lysine analogue of methotrexate, $\text{N}{}^{\mathrm{\alpha }}\text{-(}\text{4-amino-4-deoxy-10-methylpteroyl}\text{)-N}{}^{\mathrm{\epsilon }}\text{-(5-[N,N-}\text{dimethylamino]-1-naphthalenesulfonyl]-1-naphthalenesulfonyl)-}\text{l}\text{-lysine}$, is a potent inhibitor of murine L1210 dihydrofolate reductase. The dansyl fluorescence emission was enhanced approximately 3-fold with a 10 nm blue shift upon binding to L1210 dihydrofolate reductase. The fluorescent analogue was only 10-fold less potent than methotrexate in inhibiting the growth of methotrexate-sensitive and -resistant L1210 cells and competes effectively for [³H]methotrexate transport with a K_i of 7.02 μM, a value virtually identical to the K_t for methotrexate in both cell lines. In addition, strong dansyl fluorescence was found to be associated with dihydrofolate reductase from methotrexate-resistant, dihydrofolate reductase-overproducing L1210 cells following incubation of viable cells with the fluorescent methotrexate analogue for 4 hr. The results demonstrate that the dansyl-l-lysine analogue of methotrexate was rapidly transported into L1210 cells where it formed a high-affinity, fluorescent complex with intracellular dihydrofolate reductase.     

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.     

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.     

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.     

Carbon disulphide tetratogenicity and postnatal effects in rat

Pregnant albino rats were exposed to carbon disulphide vapour in concentrations of 50, 100 or 200 $\text{mg}\text{m}{}^3$throughout gestation. Two successive generations (F₁ and F₂) were studied.Concentration levels of 100 and 200 $\text{mg}\text{m}{}^3$ produced marked dose-related impairment in the prenatal development of the F₁ progeny, with increase of early embryonal lethality, reduction in foetal weight and a high incidence of malformations affecting mostly the brain and limbs. Postnatal viability, body weight, lipid and energy metabolism and behaviour were also impaired. Behavioral deviations were observed even at 50 $\text{mg}\text{m}{}^3$.After reaching sexual maturity the F₁ rats were mated within their experimental groups, but no further carbon disulphide exposure was applied. The adverse effects on progeny were still detectable in the F₂ generation. Structural abnormalities of the same type as those found in the F₁ at 100 and 200 $\text{mg}\text{m}{}^3$ exposure were observed in their progeny and, postnatally, statistically significant behavioral changes were observed in the progeny of all test groups.     

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.     

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.     

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.     

Acute tobacco smoke exposure alters the profile of metabolites produced from benzo[a]pyrene by the isolated perfused rabbit lung

The influence of whole tobacco smoke or the gas phase from smoke on the metabolism of $\text{[}{}^{14}\text{C]benzo}\text{[a]}\text{pyrene}$ was e xamined using the isolated perfused rabbit lung model. Fresh whole tobacco smoke mixed with the air ventilating the perfused lung produces an immediate and dose related decrease in the metabolism of $\text{[}{}^{14}\text{C]benzo}\text{[a]}\text{pyrene}$. The metabolites of $\text{[}{}^{14}\text{C]benzo}\text{[a]}\text{pyrene}$, diols, quinones, phenols and polar compounds are generally decreased in quantity. At the lowest level of smoke administered the percentage of BP-7,8-diol produced is increased dramatically. The results indicate that one of the factors contributing to the carcinogenicity of tobacco smoke may be its ability to produce an immediate alteration in the pulmonary metabolism of polycyclic aromatic hydrocarbons.