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In the search for more selective A2-receptor agonists and on the basis that appropriate substitution at C2 is known to impart selectivity for A\(_2\) receptors, 2-alkynyladenosines 2a-d were resynthesized and evaluated in radioligand binding, adenylate cycla.se, and platelet aggregation studies. Binding of [\(^3\)H]NECA to A\(_2\) receptors of rat striatal membranes was inhibited by compounds 2a-d with K\(_i\) values ranging from 2.8 to 16.4 nM. 2-Alkynyladenosines also exhibited high-affmity binding at solubilized A\(_2\) receptors from human platelet membranes. Competition of 2-alkynyladenosines 2a-d for the antagonist radioligand [\(^3\)H]DPCPX and for the agonist [\(^3\)H]CCPA gave K\(_i\) values in the nanomolar range, and the compounds showed moderate A\(_2\) selectivity. In order to improve this selectivity, the correaponding 2-alkynyl derivatives of adenosine-5'-N-ethyluronamide 8a-d were synthesized and tested. A\(_1\) expected, the 5'-N-ethyluronamide derivatives retained the A\(_2\) affinity whereas the A\(_1\) affinity was attenuated, resulting in an up to 10-fold increase in A\(_2\) selectivity. A similar patternwas observed in adenylate cyclase assays andin platelet aggregation studies. A 30- to 45-fold selectivity for platelet A\(_2\) receptors compared to A\(_1\) receptors was found for compounds 8a-c in adenylate cyclase studies.
Styrene-7,8-oxide (SO), the main intennediate metabolite of styrene, induces hyperkeratosis and tumors in the forestomach of rats and mice upon chronic administration by gavage. The aim of this study was to investigate wbether DNA binding could be responsible for the carcinogenic effect observed. [7-\(^3\)H]SO was administered by oral gavage in com oll to male CD rats at two dose levels (1.65 or 240 mg/kg). After 4 or 24 h, forestomach, glandular stomach and Uver were exclsed, DNA was isolated and its radioactivity detennined. At the 4 h time polnt, the DNA radioactivity was below the Iimit of detection in the torestornach and the liver. Expressed in the units of the covalent bindlng Index, CBI = (pmol adduct/mol DNA nucleotide)/(mmol cbemical administeredlkg body wt), the DNA-binding potency was below 2.6 and 2.0 respectively. In the glandular stomach at 4 b, and in most 24 b samples, DNA was slightly radiolabeled. Enzymatic degradation of the DNA and separation by HPLC ofthe normal nucleotides sbowed that the DNA rad.ioactivity represented biosynthetic incorporation of radlolabel into newly synthesized DNA. The Iimit of detection of DNA adducts in the glandular stomach was 1.0. In a second experlment, [7-\(^3\)H]SO was administered by i.p. injection to male 86C3Fl rnice. Liver DNA was analyzed after 2 h. No radloactivity was detectable at a Iimit of detection of CBI < 0.6. In agreement with the relatively long half-life of SO in animals, the cbemical reactivity of SO appears to be too low to result in a detectable production of DNA adducts in an in vivo situation. Upon comparison with the DNA-binding of other carcinogens, a purely genotoxic mechanism of tumorigenJc action of SO is unlikely. The observed tumorigenic potency in the forestomach could be the result of strong tumor promotion by high-dose cytotoxicity foUowed by regenerative hyperplasia.
Muscarinic receptors of rcsistance vessels (submucosal artcrioles, outside diametcr 50-75 J,Lm) from the guinea-pig small intestinc were invcstigatcd in vitro using a computcr-assisted vidcomicroscopy system (Diamtrak <~t ). The muscarinic receptor which mediates vasodilation of prccontractcd [U-46619 (300 nM) or (- )-noradrcnaline (1 0 J.L M)] artcriolcs was characterized with scveral muscarinic agonists and subtypc-sclectivc antagonists. Thc following agonists all produccd cquivalent maximum vasodilation (given in rank ordcr of potency): acctylcholinc = arccaidinc propargyl cstcr (APE) > oxotremorine = ( ± )-muscarinc = ( ± )-mcthacholinc > carbachol > 4-[[N-{4-chlorophenyl)carbamoyl]oxy]-2-hutynyltrimcthylammonium iodide (4-CI-McN-A- 343). 4-([N-(3-ChlorophcnyD-carbamoyl)oxy]-2-butynyltrimcthylammonium chloride (McN-A-343) and N-ethyl-guvacinc propargyl ester (NEN-APE) produccd minimal or no artcriolar vasodilation. Thc muscarinic antagonists pircnzcpinc, ( ± )-5,11-dihydro-11- [[[2-[2-((dipropylamino)methyl}-1-pipcridinyl]ethyl]amino ]-carbonyi]-6H-pyrido(2,3-h)( 1 ,4)-benzodiazcpin-6-onc (AF-DX 384 ), 11- [[ 4-[4-(dicthylamino)butyl]-1-piperidinyl]acetyl]-5, ll-dihydro-6H-pyrido(2.3-h)( 1,4 )-bcnzodiazepin-6-onc (AQ-RA 741 ), p-fluorohexahydro- sila-difcnidol (p-F-HHSiD), 4-diphcnylacetoxy-N-methylpipcridine mcthiodidc (4-DAMP) and (R)- and (S)hexahydro- difcnidol [(R)-HHD, (S)-HHD] shifted thc muscarinc, mcthacholinc or carbachol dosc-rcsponsc curve to the right in a compctitive manner. Schildanalysis of the data yicldcd pA\(_2\) valucs for pircnzcpinc (6.74/6.9), AF-DX 384 (6.72), AQ-RA 741 (6.58), p-F-HHSiD (7.53/7.57), 4-DAMP (9.06), (R)-HHD (7.88/8.32) and (S)-HHD (5.52/5.88). Thus, it can he concluded that submucosal arteriolcs posscss only the M\(_3\) functional muscarinic reccptor, the activation of which causcs hlood vcsscl dilation. The preparation dcscribcd is considcrcd to be a valuable now bioassay for pharmacological investigations of drug actions at muscarinic receptors in the peripheral vascular system.
The isolation and structure elucidation of rac-dioncophyllacine A from the leaves of Triphyophyllun peltatum, is described. Unlike all other naphthylisoquinoline alkaloids, this fully dehydrogenated representative has an additional methoxy group at C-4, the position of which is deduced from NOE results. Dioncophyllacine A has a 7,1' site of the biaryl axis, as in dioncophylline A. Its constitution is confirmed by an X-ray structure analysis, which shows that the crystalline form of this new alkaloid is racemic.
A practicable two-step procedure for the preparation of a series of lactone-type bridged biaryls 7 as favorable substrates for subsequent atropisomer-selective ring-opening reactions is described. Due to the efficiency of the coupling step, which tolerates even a telt·butyl group next to the biaryl axis and avoids problems of regioselectivity, a variety of differently substituted representatives is prepared. These cover a broad range of steric hindrance and thus molecular distortion. The structures are investigated mainly by NMR spectroscopy and X-ray diffraction, showing the lactones 7 to be helically distorted, depending on the size of the residues R.
A gene (Imsod) encoding superoxide dismutase (SOD; EC 1.15.1.1) of the facultative intracellular pathogen, Listeria monocytogenes, was cloned by functional complementation of an SOD-deficient Escherichia coli mutant. The nucleotide sequence was determined and the deduced amino acid (aa) sequence (202 aa) showed close similarity to manganese-containing SOD's from other organisms. Subunits of the recombinant L. monocytogenes SOD (re-SOD) and of both E. coli SODs formed enzymatically active hybrid enzymes in vivo. DNA/DNA-hybridization experiments showed that this type of recombinant re-sod gene is conserved within the genus Listeria.
Photoaffinity-labeled N-formyl chemotactic peptide receptors from human neutrophils solubilized in octyl glucoside exhibit two forms upon sucrose density gradient sedimentation, with apparent Sedimentation coefficients of approximately 4 and 7 S. Tbe 7 S form can be converted to the 4 S form by guanosine 5' -0- (3-thiotriphosphate) (GTP-yS) with an EC&o of -20 nM, suggesting that the 7 S form may represent a physical complex of the receptor with endogenous G protein (Jesaitis, A. J., Tolley, J. 0., Bokoch, G. M., and Allen, R. A. (1989) J. Cell Biol. 109, 2783-2790). To probe the nature of the 7 S form, we reconstituted the 7 S form from the 4 S form by adding purified G protein. The 4 S form, obtained by solubilizing GTP-yS-treated neutrophil plasma membranes, was incubated with purified (>95%) G. protein from bovine brain (containing both G\(_{ia1}\) and G\(_{ia2}\)) or with neutrophil G protein (G\(_a\)), and formation of the 7 S complex was analyzed on sucrose density gradients. The EC\(_{50}\) of 7 S complex formation induced by the two G proteins was 70 \(\pm\) 25 and 170 \(\pm\) 40 DM for G\(_a\) and G\(_1\), respectively. No complexation was measurable when bovine transducin (G\(_t\)) was used up to 30 times the EC\(_{50\) for G\(_a\). The EC\(_{50}\) for G\(_t\) was the same for receptors, obtained from formyl peptide-stimulated or unstimulated cells. The addition of 10 \(\mu\)M GTP-yS to the reconstituted 7 S complex caused a complete reversion of the receptor to the 4 S form, and anti-G\(_1\) peptide antisera immunosedimented the 7 S form. ADP-ribosylation of Gt prevented formation of the 7 S form even at 20 times the concentration of unribosylated G. normally used to attain 50% conversion to the 7 S form. These observations suggest that the 7 S species is a pbysical complex containing N-formyl chemotactic peptide receptor and G protein.
High- and low-IQ children in the first, third, and fifth grades performed two free-recall tasks: a sort-recall task with sets of categorically related pictures, and a class-recall task, with children recalling the current members of their school class. All children were deemed to be experts concerning the composition of their school class, but, unlike experts in other domains, had no special motivation associated with their expertise. Recall and clustering on both tasks were high. The high-IQ children performed better than low-IQ children only on the sort-recall task. IQ was significantly correlated with measures of performance on the sort-recall task but not on the class-recall task. The results reflect the fact that the memory benefits associated with being an expert (here, elimination of IQ effects) are related to the greater knowledge the expert possesses and not to factors of motivation.
In the present work we report the results of magneto-transport measurements on some Hg-based li-VI semiconductor epitaxiallayers grown by molecular beam epitaxy. The transport measurement were carried out at temperatures in the range 0.4 - 4.2 K in magnetic fields up to 10.0 T. Further, we point out the necessity of using multicarrier models for data interpretation and show finally some Shubnikov-de-Haas results on sampies with high mobility carners.
Nuclei assembled in Xenopus egg extract from purified DNA or chromatin resemble their natural counterparts in a number of structural and functional features. However, the most obvious structural element of normal interphase nuclei, the nucleolus, is absent from the in vitro reconstituted nuclei. By EM, cytological silver staining, and immunofluorescence microscopy employing antibodies directed against various nucleolar components we show that nuclei assembled in vitro contain numerous distinct aggregates that resemble prenucleolar bodies (PNBs) by several criteria. Formation of these PNB-like structures requires pore complex-mediated nuclear transport of proteins but is independent of the genetic content of the in vitro nuclei as well as transcriptional and translational events. Our data indicate that nuclei assembled in vitro are capable of initiating early steps of nucleologenesis but that the resulting PNBs are unable to fuse with each other, probably due to the absence of a functional nucleolus organizer. With appropriate modifications, this experimental system should be useful to define and analyze conditions promoting the site-specific assembly of PNBs into a coherent nucleolar body.
Expression of human foamy virus is differentially regulated during development in transgenic mice
(1992)
Tbe human foamy virus (HFV) is a recently characterized member ofthe spumavirus family. Although no diseases have been unequivocally associated with HFV infection, expression of HFV regulatory genes in transgenie mice induces a characteristic aeute neuro degenerative disease and a myopathy. To better eharaeterize the sequenee of events leading to disease, and to gain a better understanding of the underlying pathogenetic meehanisms, we have analyzed in detail the transgene expression pattern during development. Transcription of a construet containing all regulatory elements and aneillary genes of mv was analyzed by in situ hybridization and was shown to occur in two distinct phases. At midgestation, low but widespread expression was first deteeted in eells of extraembryonie tissues. Later, various tissues originating from embryonie mesoderm, neuroeetoderm, and neural erest transeribed the transgene at moderate levels. However, expression deereased dramatically during late gestation and was suppressed shortly after birth. After a latency period of up to 5 weeks, transeription of the transgene resumed in single eelJs distributed irregularly in the central nervous system and in the skeletal museIe. By the age of 8 weeks, an increasing number of eells displayed much higher expression levels than in embryonie Iife and eventually underwent severe degenerative ehanges. These findings demonstrate that HFV transgene expression is differentially regulated in development and that HFV cytotoxicity may be dose-dependent. Such biphasic pattern of expression differs from that of murine retroviruses and may be explained by the specificity of HFV regulatory elements in combination with cellular faetors. Future studies of this model system should, therefore, provide novel insights in the mechanisms controlling retrovirallatency.
Cardio-respiratory changes and mortality in the conscious rat induced by (+)- and (±)- anatoxin-a
(1992)
0. M. ADEYEMO and A.-L. SIREN. Cardio-respiratory changes and mortality in the conscious rat induced by ( + )- and ( ± )-anatoxin-a. Toxicon 30, 899-905, 1992.-Anatoxin-a (AnTx-a) isapotent nicotinic cholinergic receptor agonist. The relative potencies of the ( + )-AnTx-a and the racemic mixture ( ± )-AnTxa were investigated in the conscious rat by comparing their effects on mean arterial blood pressure (BP), heart rate (HR), blood oxygen and carbon dioxide pressures (p02 and pC02, respective1y), acid-base balance (pH) and mortality. The present experiments show that while both forms of AnTx-a produce dose-dependent increases in BP and decreases in HR, ( + )-AnTx-a is about IO-fo1d morepotent than the optically inactive isomer. ( + )-AnTx-a was also 6-fo1d more potent than ( ± )-AnTx-a in produclog severe hypoxemia, and more than 4-fold as potent as the (±}-AnTx-a in producing significant hypercapnia accompanied with severe acidosis. The approximate median Iethai dose (Ln so) of ( + )-AnTx-a was about 5-fold less than that of ( ± )-AnTx-a. We conclude that ( + )-AnTx-a is more potent than the ( ± )-AnTx-a racemic mixture in causing detrimental cardio-respiratory changes and therefore increased mortality in the rat.