Interactions of trichloroethylene with DNA in vitro and with RNA and DNA of various mouse tissues in vivo

The covalent binding of 14C-1,1,2-trichloroethylene (14C-TRI) metabolites to calf thymus DNA in vitro and to RNA and DNA of mouse brain, lung, liver, kidney, spleen, pancreas, and testis after repeated i.p. injections has been studied. Hydrolysates of DNA reacted with 14C-TRI in vitro and hydrolysates of RNA and DNA from selected organs were separated on Aminex A6 for quantitation of alkylation products. The presence of 3,N4-etheno(deoxy)cytidine, 1,N6-etheno(deoxy)adenosine and 1,N6-ethenoadenine was investigated. No radioactivity could be registered in DNA incubated with 14C-TRI in the absence of liver microsomes. Covalent binding of 14C-TRI to DNA took place in the presence of liver microsomes from control mice. The binding was enhanced by 50% if liver microsomes from phenobarbital pretreated mice were used. The radioactivity in DNA reacted with 14C-TRI and microsomes from control mice was eluted in early fractions and together with thymidine. The same two peaks appeared on chromatography of DNA incubated with 14C-TRI and liver microsomes from phenobarbital pretreated mice. In addition, radioactivity was eluted together with 1,N6-ethenoadenine. Radioactivity was registered in RNA and DNA from all of the studied organs after i.p. injections of 14C-TRI. The radioactivity in RNA increased in the order brain less than testis less than pancreas less than kidney less than liver less than lung less than spleen. The radioactivity in DNA increased in the order brain less than kidney less than testis less than lung less than pancreas less than liver less than spleen. Aminex A6 chromatography revealed that the entire radioactivity in RNA from liver and kidney and in DNA from kidney, testis, lung, pancreas, and spleen was due to metabolic incorporation, particularly into guanine and adenine. This finding indicates that the C-C bond in TRI is split, with the formation of C1-fragments, during biotransformation in vivo. In liver DNA, the metabolic incorporation of radioactivity was insignificant. Instead, the dominant part of the radioactivity in liver DNA was eluted in early fractions. The elution profile of radioactivity in liver DNA gave no direct evidence of the formation of TRI-DNA adducts in vivo. No etheno-derivatives were identified as alkylation products of TRI in vivo, which is consistent with current theories of the metabolic fate of TRI.     

Alkylation of RNA by vinyl bromide metabolites in vitro and in vivo

[1,2-¹⁴C]Vinyl bromide was incubated with rat liver microsomes, NADPH, and polyadenylic acid, polycytidylic acid, or RNA, respectively. Part of the adenosine moieties in RNA or in polyadenylic acid were alkylated and labelled 1,N⁶-ethenoadenosine structures were formed. Part of the cytidine moieties were converted into 3,N⁴-ethenocytidine. In addition, a further unidentified cytidine alkylation product was observed which was not seen in experiments using [1,2-¹⁴C]vinyl chloride. When rats were exposed to [1,2-¹⁴C]vinyl bromide, radioactive ethenoadenosine and ethenocytidine were present in hydrolysates of liver RNA. A further alkylation product was observed in the RNA hydrolysates which did not occur in experiments using [¹⁴C]vinyl chloride. The data show that vinyl bromide metabolites alkylate nucleic acids; although in general in this respect vinyl bromide and vinyl chloride behave similarly, some differences are observed in the alkylation behaviour of both compounds.     

Formation of 3,N4-ethenocytidine moieties in RNA by vinyl chloride metabolites in vitro and in vivo

Rats were exposed to [1,2-¹⁴C] vinyl chloride. Liver RNA was isolated, hydrolyzed, and the nucleosides separated on Aminex-A-6. Besides the physiological bases and 1,N⁶-ethenoadenosine, radioactivity was also incorporated into 3,N⁴-ethenocytidine. Radioactive 3,N⁴-ethenocytidine moieties were also formed on incubation of polycytidylic acid with rat liver microsomes, NADPH and [¹⁴C] vinyl chloride. These alkylation mechanisms are consistent with the mutagenic and cancerogenic properties of vinyl chloride.

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Zusammenfassung RNS wurde aus der Leber von Ratten, die einer Atmosphäre mit [1,2-¹⁴C] Vinylchlorid ausgesetzt waren, isoliert. Nach enzymatischer Hydrolyse und Trennung der Nukleoside auf Aminex-A-6 wurde außer den physiologischen Nukleosiden und dem bereits beschriebenen 1,N⁶-Äthenoadenosin auch ein Radioaktivitätseinbau in 3,N⁴-Äthenocytidin gefunden. Eine Bildung von 3,N⁴-Äthenocytidinresten wurde auch beobachtet, wenn Polycytidylsäure, Rattenlebermikrosomen, NADPH-regenerierendes System und [¹⁴C] Vinylchlorid inkubiert wurden.

     

Reaction of benzyl chloride with haemoglobin and DNA in various organs of mice

[¹⁴C]Benzyl chloride was given i.v. to male mice and the elimination of the radioactivity from various organs was studied. The alkylation of guanine-N-7 of DNA in the same organs and the alkylation of haemoglobin were determined 1, 6 and 24 h after injection of benzyl chloride.There was a decrease with time of the degree of alkylation of DNA in brain, testis and liver, but an increase in lung and probably also spleen. The degree of alkylation of haemoglobin also increased.The expected degree of alkylation of DNA was calculated from the degree of alkylation of haemoglobin. The ratio of found and expected degree of alkylation of DNA was about 3 times higher for testis and brain than for the other organs 1 h after administration of benzyl chloride.     

10-羟基癸烯酸在动物体内吸收、分布、代谢和排泄

10-癸基癸烯酸(即10-HDA,定位标记为³H-10HDA),经小鼠和大鼠口服后,胃肠道吸收快,峰时均在1h,全身分布迅速广泛,与组织亲和力强,肝中放射性为最高,依次为肾、胰、脂肪、脑、脾、心和肺。平均Vd为9.71/kg。Ig和iv的T1/2β在12.6～22.7h。体内消除较缓慢,31 d内,尿粪中放射性累计排泄分别为给药量的85.4%和13.5%,提取尿和胆汁经分析结果主要以原形药物排出。血浆蛋白结合率为63%。血中放射—性时间曲线符合开放二室模型。     

Alkylation of RNA by vinyl chloride metabolites in vitro and in vivo: Formation of 1-N6-etheno-adenosine

Rat liver microsomes were incubated with NADPH, 1,2-[¹⁴C]vinyl chloride and poly-adenosine. The latter was reisolated from the incubations and hydrolyzed. The radioactivity, originating from [¹⁴C]vinyl chloride, which was irreversibly attached to the poly-adenosine was confined to 1-N⁶-etheno-adenosine (3β-ribofuranosyl-imidazo[2,1,i] purine). When rats were exposed to 1,2-[¹⁴C]vinyl chloride, part of the radioactivity was incorporated into RNA of liver. This radioactive labelling exhibited a first maximum, 14 h, and a second maximum, 72 h after ending the exposure. Analysis of hydrolysate of liver RNA showed that all natural nucleosides of RNA were labelled. Besides, small amounts of radioactivity could be detected which were confined to 1-N⁶-etheno-adenosine. The experiments support the theory that vinyl chloride metabolites react with adenosine moieties of nucleic acid under formation of 1-N⁶-etheno-adenosine. Furthermore, the results show that measurement of incorporation of radioactivity into nucleic acids after exposure of animals to radioactive vinyl chloride is not applicable as a means of determining the alkylating potency of vinyl chloride metabolites towards nucleic acids in vivo.     

S-adenosyl- -methionine N-ole-1-oyltaurate: pharmacokinetic of the orally administered salt in rats

A pharmacokinetic study based on the distribution of radioactivity from the double labelled S-adenosyl- -methionine (SAM) has been carried out by oral administration of the liposoluble stable salt [methyl-¹⁴C, 8-³H]SAM N-ole-1-oyltaurate to rats. The SAM sulfate p-toluensulfonate salt, the only SAM salt at present commercialized as drug, was chosen as reference compound to have a comparative pharmacokinetic analysis. The metabolism of the SAM is characterised by a differential use of the two labelled moieties by the various organs, liver being the most active in metabolizing the sulfonium compound with a preferential uptake of the methyl-¹⁴C fragment. The radioactivity detected after the administration of [methyl-¹⁴C, 8-³H]SAM N-ole-1-oyltaurate is, in all the organs examined, two times higher than the [methyl-¹⁴C, 8-³H]SAM sulfate p-toluensulfonate compound, attesting that the liposoluble [methyl-¹⁴C, 8-³H]SAM N-ole-1-oyltaurate is provided with better bioavailability.     

Probenecid,an inhibitor of transmembrane organic anion transporters,alters tissue distribution of DNA adducts in 1-hydroxymethylpyrene-treated rats

1-Methylpyrene (1-MP), an abundant alkylated polycyclic aromatic hydrocarbon, is activated by side-chain hydroxylation to 1-hydroxymethylpyrene (1-HMP) and subsequent sulfo-conjugation to electrophilic 1-sulfooxymethylpyrene (1-SMP). In rats, this activation mainly occurs in liver. 1-SMP may react with hepatic DNA or be exported into the blood circulation to reach other tissues, in particular kidneys. Findings with recombinant cell lines suggest that renal 1-SMP uptake proceeds via organic anion transporters (OATs). Here, we tested the hypothesis that probenecid, a characteristic OAT inhibitor, interferes with kidney damage brought about by 1-SMP formed in rats. 1-HMP was administered intraperitoneally to 30 rats, half of which were co-treated with probenecid. The tissue distribution of DNA adducts was analyzed using ³²P-postlabeling and isotope dilution LC–MS/MS for the detection of the adducts N²-(1-methylpyrenyl)-2′-deoxyguanosine and N⁶-(1-methylpyrenyl)-2′-deoxyadenosine. In rats treated solely with 1-HMP, adduct levels in kidney tissue were about 3-fold and 8-fold higher than those in liver and lung, respectively. After co-treatment with probenecid, hepatic and pulmonary adduct levels were 12-fold and 4-fold elevated, respectively, whereas renal adduct levels were slightly lower compared to those of rats receiving 1-HMP alone. Moreover, serum levels of 1-SMP were increased 23-fold in animals pre-treated with probenecid. The differential effects on hepatic and pulmonary adduct levels suggest that not only renal OATs, but also additional anion transporters, e.g. those mediating the hepatic export of 1-SMP into the bile, were inhibited. Thus, transmembrane transport proteins play a crucial role in the distribution of reactive phase II metabolites, and thereby in tissue allocation of DNA adducts.     

Whole body autoradiography of 3H-phencyclidine in mice

The present whole-body autoradiographic study demonstrates that the circulatory system is practically free of radioactivity, already 5 min after intravenous administration of ³H-Phencyclidine to mice. At this time, however, high radioactive levels appear in the lachrymal gland, nasal mucosa, bone marrow and spleen, as well as in the urinary, digestive, respiratory and reproductive systems. High accumulation is maintained up to 20 min after adminstration and, thereafter, radioactivity declines continuously with increasing time. After 6 h, radioactivity disappears in most organs, but remains notable in the kidney, lung and liver, as well as in the salivary and lachrymal glands. After 24 h, detectable amounts still persist in the liver, lung and in the salivary and lachrymal glands. The brain shows very low amounts of radioactivity during the whole period of observation. In pregnant mice, the drug accumulates in the placenta and partly crosses the placental barrier into the foetal tissues.     

疟疾防治药物的研究——Ⅹ.2,4-二氨基-6-N1,N2-二取代肼基-喹唑啉类衍生物的合成及其抗疟作用

本文报道了2,4-二氨基-6-N¹,N²-二取代肼基-喹唑啉类衍生物的合成及其抗疟活性的研究。这类化合物的合成是以2,4-二氨基6-取代苄基氨基-喹唑啉为原料经亚硝化、还原成为2,4-二氨基6-(N¹-取代苄基)—肼基喹唑啉,再与相应的醛缩合而成。此类化合物经伯氏鼠疟原虫抑制性治疗初筛表明有少数具有一定的效果。有11个化合物经约氏鼠疟原虫—斯氏按蚊系统病因性初筛有效。其中化合物Ⅱ_1,7,8,11,15和Ⅲ₁口服2.5mg/kg,连续3天,可使受试小鼠全部得到保护。     

Some aspects of metabolic activation of chemical carcinogens in relation to their organ specificity

The role of organ-specific, enzymic release of alkylating intermediates in determining which tissue develops a tumour in response to a given N-nitrosamine has been evaluated on the basis of published data on the carcinogenicity of 62 N-nitrosamines that induce tumours in specific tissues in rats. A good correlation was noted between the metabolic capacity for N-nitrosamine activation and the organ in which tumours are induced. A relationship was also noted between the localization of carcinogen activating enzymes in rat tissues and the site at which the tumour developed following administration of N-(acetoxy) methyl-N-methylnitrosamine. This compound was shown to be cleaved by soluble enzymes equally efficiently in various rat tissues, such as liver, kidney, spleen and small intestinal mucosa, to yield the alkylating and mutagenic intermediates which are presumably those also formed from the parent N,N-dimethylnitrosamine by microsomal enzymes. N-(acetoxy)methyl-N-methylnitrosamine causes tumours of the gastrointestinal tract, although the parent N,N-dimethylnitrosamine rarely affects this site in rats.The neurotropic carcinogen 3,3-dimethyl-1-phenyltriazene is known to undergo predominantly in the rodent liver oxidative N-mono-demethylation by microsomal enzymes to yield a carcinogenic, mutagenic, and alkylating intermediate, 3-methyl-1-phenyltriazene; however the parent compound produces extrahepatic tumours exclusively. To explain this alternative model of organ specificity, the half-life of 3-methyl-1-phenyltriazene was measured and found to be long enough to permit its distribution throughout the body. Furthermore, subcutaneous injection of 3-[C¹⁴-methyl]-1-phenyltriazene into rats yielded alkylated bases in nucleic acids of hepatic and extrahepatic tissues including brain, the major target organ of the parent compound 3,3-dimethyl-1-phenyltriazene. Eight hours after injection of 3-methyl-1-phenyltriazene the O ⁶ N ⁷-methylguanine ratio was found to be lowest in the liver and highest in the brain, indicating a low rate of O ⁶-methylguanine excision. Thus, for this carcinogen, the persistence of alkylated DNA bases may be a final determinant in tissue specific induction of tumours.The implications of these data for the use of in vitro metabolic activation systems in short-term tests for detecting potential carcinogens are discussed.Presented at the Symposium Influence of Metabolic Activations and Inactivations on Toxic Effects held at the 18th Spring Meeting of the Deutsche Pharmakologische Gesellschaft, Section Toxicology, D-6500 Mainz, March 15, 1977     

Biodistribution of Mixed Fluorocarbon–Hydrocarbon Dowel Molecules Used as Stabilizers of Fluorocarbon Emulsions: A Quantitative Study by Fluorine Nuclear Magnetic Resonance (NMR)

¹⁹F NMR spectroscopy was used to determine quantitatively the organ distribution and organ retention time in rats of the mixed fluorocarbon–hydrocarbon dowel molecule C₆F₁₃CH = CHC₁₀H₂₁ (F6H10E), which stabilizes highly concentrated injectable fluorocarbon emulsions destined for in vivo oxygen transport and delivery. The only fluorine resonances detected in the ¹⁹F NMR spectra of the organs analyzed were those of the F6H10E dowel itself, indicating that metabolites, if present, have very low concentrations (<10^–4 M, limit of our assay). The F6H10E content in the liver peaked 1 day after administration (7 days for the spleen). At a dose of 3.6 g/kg body weight, the half-life of F6H10E in the liver was 25 ± 5 days.     

Hepatic macromolecular binding following exposure to vinyl chloride

Covalent binding of radioactivity to hepatic macromolecules in rats exposed to ¹⁴C-labeled vinyl chloride (VC) was studied to determine if VC-induced carcinogenesis may be related to electrophilic alkylation of macromolecules in vivo. Male Sprague-Dawley rats were exposed to 1, 10, 25, 50, 100, 250, 500, 1000, or 5000 ppm of [¹⁴C]VC for 6 hr. Following exposure, radioactivity covalently bound to hepatic macromolecules and purified nucleic acids (RNA, DNA) was determined. The total amount of [¹⁴C]VC metabolized and hepatic glutathione (GSH) content were also determined. The total amount of radioactivity bound to macromolecules in the liver did not increase proportionately to the increase in the exposure concentration of VC. A disproportionate decrease in macromolecular binding was observed as the concentration of VC increased. The covalent binding to hepatic macromolecules was related to the amount of VC metabolized. At exposures greater than 50 ppm, the amount of ¹⁴C bound to macromolecules in the liver correlates with induction of hepatic angiosarcoma. There was no detectable binding of radioactivity to either DNA or RNA in the liver. Hepatic glutathione content was significantly depressed only at exposure concentrations greater than 100 ppm.     

Lipopolyamine-Mediated Single Nanoparticle Formation of Calf Thymus DNA Analyzed by Fluorescence Correlation Spectroscopy

Purpose The aim of this study is to analyze linear calf thymus DNA (ct DNA) nanoparticle formation with N⁴,N⁹-dioleoylspermine and N¹-cholesteryl spermine carbamate. Methods Fluorescence correlation spectroscopy (FCS) was used to determine the quality of ct DNA condensed by lipopolyamines. ct DNA was prelabeled with PicoGreen (PG) to allow fluorescence intensity fluctuation measurement and analysis. Results N⁴,N⁹-Dioleoylspermine efficiently condensed ct DNA into point-like molecules with diffusion coefficient (D) = 1.8 × 10⁻¹² m²/s and particle number (PN) = 0.7 [at ammonium/phosphate (N/P) charge ratio=1.0–1.5]. The determined PN values are close to the theoretical value of 0.6, providing evidence that the DNA conformation has been fully transformed, and thus a single nanoparticle has been detected. N¹-Cholesteryl spermine carbamate showed (slightly) poorer DNA condensation efficiency, even at higher N/P ratios (N/P = 1.5–2.5) with D = 1.3 × 10⁻¹² m²/s and PN value of 5.2. N⁴,N⁹-Dioleoylspermine is a more efficient DNA-condensing agent than N¹-cholesteryl spermine carbamate. Conclusions FCS measurement using PG as the probe is a novel analytical method to detect single nanoparticles of condensed DNA in nonviral gene therapy formulation studies.     

Species difference in the binding of aflatoxin B1 to hepatic macromolecules

The binding of [¹⁴C]aflatoxin B₁ to the RNA, DNA, and protein of liver after ip administration to adult rats, mice, and guinea pigs and of the in vitro binding to the plasma protein of these species was studied. Binding to nucleic acids was greater than to liver protein in all three species. Binding to hepatic macromolecules and plasma of mice was considerably less than that of the other two animal species. The specific radioactivity of guinea pig liver RNA and protein was higher than the corresponding fractions in rat liver, which correlates with the higher reported acute sensitivity of guinea pigs than rats to aflatoxin B₁. Guinea pig liver DNA, however, contained somewhat less radioactivity than did rat liver DNA, which may be related to the resistance of the guinea pig to the hepatocarcinogenicity of aflatoxin B₁.     

[125I] N6-p-hydroxyphenylisopropyladenosine,a new ligand for Ri adenosine receptors

Summary N⁶-p-Hydroxyphenylisopropyladenosine (HPIA) has been labelled with carrier-free Na[¹²⁵I] to very high specific activity (2,175 Ci/mmol) and used as an agonist ligand to characterize R_i adenosine receptors in rat cerebral cortex membranes. The binding is saturable, reversible, stereospecific and dependent on protein concentration. The specific binding at 37°C was of high affinity with an equilibrium dissociation constant K_D of 0.48 nmol/l and was saturable with 0.23 pmol of [¹²⁵I]HPIA per mg of protein. The rate constant of association, k₁, was 3.25×10⁸ l mol^–1 min^–1 and that of dissociation, k₂, 0.0110 min^–1 yielding a t_1/2 of 63 min. In competition experiments the (–)isomer of N⁶-phenylisopropyladenosine (PIA) was 16-fold more potent than the (+)isomer in competing for the binding sites. Specific binding was most effectively displaced by N⁶-cyclohexyladenosine (CHA, k_i=0.26 nmol/l), (–)PIA (k_i=0.33 nmol/l) and HPIA (k_i=0.52 nmol/l), whereas 5-N-ethylcarboxamidoadenosine (NECA, k_i-1.42 nmol/l) was less effective. The methylxanthines 3-isobutyl-1-methylxanthine (IBMX), theophylline and caffeine which have been classified as adenosine antagonists had k_i values between 5–34 mol/l. Binding of [¹²⁵I]HPIA was regulated by guanine nucleotides and divalent cations. The results indicate that [¹²⁵I]HPIA labels R_i adenosine receptors in rat brain membranes.     

Adenosine A1 receptor agonist N6-cyclohexyladenosine induced phosphorylation of delta opioid receptor and desensitization of its signaling

Aim:

To define the effect of adenosine A₁ receptor (A₁R) on delta opioid receptor (DOR)-mediated signal transduction.

Methods:

CHO cells stably expressing HA-tagged A₁R and DOR-CFP fusion protein were used. The localization of receptors was observed using confocal microscope. DOR-mediated inhibition of adenylyl cyclase was measured using cyclic AMP assay. Western blots were employed to detect the phosphorylation of Akt and the DOR. The effect of A₁R agonist N⁶-cyclohexyladenosine (CHA) on DOR down-regulation was assessed using radioligand binding assay.

Results:

CHA 1 μmol/L time-dependently attenuated DOR agonist [D-Pen^2,5]enkephalin (DPDPE)-induced inhibition of intracellular cAMP accumulation with a t_1/2=2.56 (2.09–3.31) h. Pretreatment with 1 μmol/L CHA for 24 h caused a right shift of the dose-response curve of DPDPE-mediated inhibition of cAMP accumulation, with a significant increase in EC₅₀ but no change in E_max. Pretreatment with 1 μmol/L CHA for 1 h also induced a significant attenuation of DPDPE-stimulated phosphorylation of Akt. Moreover, CHA time-dependently phosphorylated DOR (Ser363), and this effect was inhibited by A₁R antagonist 1,3-Dipropyl-8-cyclopentylxanthine (DPCPX) but not by DOR antagonist naloxone. However, CHA failed to produce the down-regulation of DOR, as neither receptor affinity (K_d) nor receptor density (B_max) of DOR showed significant change after chronic CHA exposure.

Conclusion:

Activation of A₁R by its agonist caused heterologous desensitization of DOR-mediated inhibition of intracellular cAMP accumulation and phosphorylation of Akt. Activation of A₁R by its agonist also induced heterologous phosphorylation but not down-regulation of DOR.     

Nature of the N6 region of the adenosine receptor in guinea-pig ileum and rat vas deferens

Summary This study explored the nature of the purine domain N⁶ regions of the presynaptic adenosine receptors of guinea-pig ileum and of rat vas deferens. The experimental design tested a model of these receptors which is complementary to the structure of the N⁶ substituent of the classical A₁ adenosine receptor agonist N⁶-1-phenyl-2R-propyladenosine, (R-PIA). Assays of activity employed ileal segments or the midportions of vasa deferentia under continuous electrical stimulation at 0.2 Hz. Structure activity correlations compared the EC-50s for twitch inhibition.As shown previously, R-PIA was 60–80 times more potent than its S diastereomer, the resultant of the positive contribution of propyl C-3 to activity as well as the negative influence of steric hindrance exerted by propyl C-3 of the S diastereomer. Other pairs of diastereomers having a chiral center adjacent to N⁶ showed that the stereoselectivity of the PIAs was generalizable. Biological activity appears to reside wholly in the N⁶ alkyl moiety; the phenyl or aryl groups of similar size actually diminished potency. The receptor subregions interacting with propyl C-1 and C-3 of R-PIA are each large enough to accomodate two — but not three — methylene residues, each methylene contributing additively to activity. Hydrophobicity is a prominent attribute of the propyl C-1 and C-3 subregions.The potencies of these analogs as inhibitors of presynaptic transmission in ileum or vas deferens are covariant with inhibition of [³H]N⁶-cyclohexyl-adenosine binding to rat cerebral cortical membranes. Singular exceptions to this generalization may represent organ- or species-dependent differences in receptor fine structure.     

Positron emission tomography of [18F]-big endothelin-1 reveals renal excretion but tissue-specific conversion to [18F]-endothelin-1 in lung and liver

Background and purpose:

Big endothelin-1 (ET-1) circulates in plasma but does not bind to ET receptors until converted to ET-1 by smooth muscle converting enzymes. We hypothesized that tissue-specific conversion of [¹⁸F]-big ET-1 to [¹⁸F]-ET-1 could be imaged dynamically in vivo within target organs as binding to ET receptors.

Methods:

[¹⁸F]-big ET-1 conversion imaged in vivo following infusion into rats using positron emission tomography (PET).

Key results:

[¹⁸F]-big ET-1 was rapidly cleared from the circulation (t_1/2= 2.9 ± 0.1 min). Whole body microPET images showed highest uptake of radioactivity in three major organs. In lungs and liver, time activity curves peaked within 2.5 min, then plateaued reaching equilibrium after 10 min, with no further decrease after 120 min. Phosphoramidon did not alter half life of [¹⁸F]-big ET-1 but uptake was reduced in lung (42%) and liver (45%) after 120 min, consistent with inhibition of enzyme conversion and reduction of ET-1 receptor binding. The ET_A antagonist, {"type":"entrez-nucleotide","attrs":{"text":"FR139317","term_id":"258103156","term_text":"FR139317"}}FR139317 did not alter half-life of [¹⁸F]-big ET-1 (t_1/2= 2.5 min) but radioactivity was reduced in all tissues except for kidney consistent with reduction in binding to ET_A receptors. In kidney, however, the peak in radioactivity was higher but time to maximum accumulation was slower (∼30 min), which was increased by phosphoramidon, reflecting renal excretion with low conversion and binding to ET receptors.

Conclusions and implications:

A major site for conversion was within the vasculature of the lung and liver, whereas uptake in kidney was more complex, reflecting excretion of [¹⁸F]-big ET-1 without conversion to ET-1.This article is part of a themed section on Imaging in Pharmacology. To view the editorial for this themed section visit http://dx.doi.org/10.1111/j.1476-5381.2010.00685.x     

Autoradiographische und radiochromatographische Untersuchungen der Verteilung und des Stoffwechsels von Thioacetamid

Summary The distribution of³⁵S-thioacetamide after a large dose (40 mg/100 g) was investigated in thirteen rats using whole-body autoradiography. Control experiments were made on six rats which were given³⁵S-sodium sulphate in order to differentiate the radioactivity due to³⁵S-thioacetamide from that due to metabolically formed sulphate. In addition, extracts of various organs, faeces and urine from five other rats were examined using Chromatographic separation methods.The results show that there is an accumulation of thioacetamide or thioacetamide sulphoxide in the centres of the liver lobules, in the outer medullary portion of the kidney, in the heart muscle, spleen and lymph nodes, in the mucous membranes of the stomach and the intestine and also in the gastric and intestinal contents. After the administration of a large dose of³⁵S-thioacetamide about 80% of the radioactivity is excreted in the urine as thioacetamide or its sulphoxide within 24 hours. A small fraction is eliminated through the gastro-intestinal tract.Our findings suggest that in thioacetamide poisoning there is a correlation between organ damage and the concentration of the poison in the organ, especially in the liver.

Die Autoradiographien wurden im Pharmakologischen Institut der Freien Universität (Direktor: Prof. Dr. Herken) hergestellt). Für die Unterstützung bei der Durchführung der Arbeiten haben wir Herrn Prof. Dr. Koransky sehr zu danken.Frl. C. Eulenstedt leistete hervorragende technische Assistenz.