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Biomedical subjects

V G Wilson

Publications and source records attributed to V G Wilson.

At least 91 records · Page 5Linked to original sources
PubMed1988

Activities of octopamine and synephrine stereoisomers on alpha-adrenoceptors.

1. The activities of the (-)- and (+)-forms of m- and p-octopamine and m- and p-synephrine on alpha 1-adrenoceptors from rat aorta and anococcygeus and alpha 2-adrenoceptors from rabbit saphenous vein were compared with those of noradrenaline (NA). 2. The rank order of potency of the (-)-forms on alpha 1-adrenoceptors from rat aorta and alpha 2-adrenoceptors was NA greater than m-octopamine = m-synephrine greater than p-octopamine = p-synephrine. The two m-compounds were 6 fold less active than NA on alpha 1-adrenoceptors from rat aorta and 150 fold less active on alpha 2-adrenoceptors. The two p- compounds were 1,000 fold less active than NA on both alpha 1-adrenoceptors from rat aorta and alpha 2-adrenoceptors. The rank order of potency of the (-)- forms on alpha 1-adrenoceptors from rat anococcygeus was NA = m-synephrine greater than m-octopamine greater than p-octopamine = p-synephrine. m-Octopamine was 4 fold less active than NA and (-)-m-synephrine. The two p- compounds were 30 fold less active than NA. 3. The rank order of potency of the (+)- forms was NA greater than m-octopamine greater than m-synephrine greater than p-octopamine greater than p-synephrine on both alpha 1- and alpha 2-adrenoceptors. The potency of each (+)- form was 1-2 orders of magnitude less than that of the (-) counterpart, the differences being greater for the stereoisomers of synephrine than for those of octopamine on both alpha 1- and alpha 2-adrenoceptors. 4. The yohimbine diastereoisomer antagonists, rauwolscine and corynanthine, were tested against (-)-NA and (-)-m-octopamine-induced contractions in both preparations. Based upon the known selectivities of these isomers for alpha-adrenoceptor subtypes, it is concluded that the rat aorta contains only alpha 1-adrenoceptors while the rabbit saphenous vein possesses predominantly alpha 2-adrenoceptors. 5. Ligand binding data for the octopamine and synephrine stereoisomers at alpha 1- and alpha 2-binding sites from rat cerebral cortex was also obtained. (-)-Forms were more active than (+)-forms. The rank order of affinity of the (-)-forms for both alpha 1- and alpha 2-binding sites was NA greater than m-octopamine = m-synephrine greater than p-synephrine greater than p-octopamine. The relative affinities of the members of the series against alpha 1-binding sites were very similar to their relative functional activities on rat aorta. However, the affinities of both m- and p-compounds relative to that of ( -)-NA were much greater at the x2-binding sites than were the relative activities in rabbit saphenous vein, possibly suggesting low intrinsic efficacy. Functional antagonist responses to NA by the (-)-octopamine and synephrines could not, however, be demonstrated on rat aorta or rabbit saphenous vein. 6. The activities of m-octopamine and m-synephrine were not significantly different from each other on either a,-adrenoceptors from rat aorta or x2-adrenoceptors; however, m-synephrine is more active than m-octopamine on a,-adrenoceptors from rat anococcygeus. Both m-octopamine and msynephrine can be considered to be naturally occurring x,-selective amines. However, if m- and poctopamine are co-released with NA in amounts proportional to their concentration, it is concluded that their activities on m,- and x2-adrenoceptors are too low to be physiologically significant.

2-Hydroxyphenethylamine↗
PubMed1988

Evidence that the population of postjunctional-adrenoceptors mediating contraction of smooth muscle in the rabbit isolated ear vein is predominantly alpha 2.

1. Noradrenaline (NA), phenylephrine and UK-14304 elicited concentration-dependent contractions of the rabbit isolated ear vein of similar maximal magnitude. The rank order of potency, UK-14304 greater than noradrenaline greater than phenylephrine, is consistent with that of an effect mediated through an alpha 2-subtype. 2. The potent and highly selective alpha 1-adrenoceptor antagonists prazosin and YM-12617, at concentrations as high as 1 microM, produced less than a 4 fold rightward displacement of the NA concentration-response curve. 3. The selective alpha 2-adrenoceptor antagonists rauwolscine, Wy-26703 and CH-38083 antagonized responses to noradrenaline in a competitive manner. For all three antagonists, the pA2 values were consistent with an effect at alpha 2-adrenoceptors. However, 0.1 microM YM-12617 increased the potency of rauwolscine 2 fold indicating the presence of a small population of postjunctional alpha 1-adrenoceptors. 4. The relative antagonist potency of the yohimbine diastereoisomers rauwolscine and corynanthine against noradrenaline (rauwolscine 30 fold greater than corynanthine) is also consistent with an effect at alpha 2-adrenoceptors. 5. Contractions elicited by noradrenaline in the rabbit isolated ear vein appear to be mediated predominantly by postjunctional alpha 2-adrenoceptors.

Adrenergic alpha-Antagonists↗
PubMed1988

An examination of the postjunctional alpha-adrenoceptor subtypes for (-)-noradrenaline in several isolated blood vessels from the rabbit.

1. Postjunctional alpha-adrenoceptors in several isolated blood vessels from the rabbit have been characterized on the basis of the relative potency of the agonists noradrenaline (NA, non-selective), phenylephrine (alpha 1-selective) and UK-14304 (alpha 2-selective), and the potency of antagonists rauwolscine (alpha 2-selective) and corynanthine (alpha 1-selective) against contractions elicited by NA. In addition, the potency of prazosin against NA was also assessed in the venous preparations. 2. The thoracic aorta, ear artery and left renal vein appear to possess alpha 1-adrenoceptors since the agonist potency order was NA greater than phenylephrine greater than UK-14304, while corynanthine was 3-10 fold more potent than rauwolscine. 3. The ear vein appears to possess alpha 2-adrenoceptors. The rank order of agonist potency was UK-14304 greater than NA much greater than phenylephrine and all three agonists elicited responses of similar magnitude. Furthermore, rauwolscine was 30 fold more potent than corynanthine while prazosin failed to produce a concentration-dependent inhibition. 4. The saphenous vein and the plantaris vein appear to possess a mixture of both subtypes since the rank order of agonist potency was UK-14304 greater than NA much greater than phenylephrine, while responses elicited by UK-14304 were smaller than those to the other agonists. However, although rauwolscine was 20 to 100 fold more potent than corynanthine in both preparations, suggestive of predominantly alpha 2-adrenoceptors, prazosin was either potent (saphenous vein) or relatively inactive (plantaris vein). 5. The characteristics of postjunctional alpha 1- and alpha 2-adrenoceptors on isolated blood vessels from the rabbit are discussed in relation to the value of both the agonists, particularly NA, and the antagonists used in this study.

Animals↗
PubMed1988

Pharmacological analysis of postjunctional alpha-adrenoceptors mediating contractions to (-)-noradrenaline in the rabbit isolated lateral saphenous vein can be explained by interacting responses to simultaneous activation of alpha 1- and alpha 2-adrenoceptors.

1. The pharmacological characteristics of the alpha-adrenoceptor population in the rabbit isolated saphenous vein has been examined with (-)-noradrenaline (NA), as principal agonist, and a number of antagonists with selectivity for either alpha 1- or alpha 2-adrenoceptors. 2. The rank order of potency of various agonists is consistent with a population of alpha 2-adrenoceptors; UK-14304 greater than (-)-noradrenaline = (-)-adrenaline greater than B-HT 920 = cirazoline greater than phenylephrine greater than amidephrine, but the rank order of pA2 values for the antagonists against (-)-noradrenaline: BDF-6143 greater than rauwolscine = prazosin greater than CH-38083 = YM-12617 greater than Wy-26703 = phentolamine greater than corynanthine, is indicative of a mixed population of alpha 1- and alpha 2-adrenoceptors or, alternatively, a new subtype with characteristics of both the alpha 1- and alpha 2-subtypes. 3. Further evidence for two discrete populations of alpha-adrenoceptors is provided by, (a) the potent but non-competitive effect of prazosin against (-)-noradrenaline, (b) the presence of a component of the contractions elicited by NA and phenylephrine which is resistant to the selective alpha 2-adrenoceptor antagonists rauwolscine and CH-38083: these responses were inhibited by the selective alpha 1-adrenoceptor antagonists prazosin and YM-12617, but not by the selective alpha 2-adrenoceptor antagonist BDF-6143 and, (c) the relative potency of the yohimbine diastereoisomers rauwolscine and corynanthine against NA, phenylephrine and UK-14304. 4. In spite of the overwhelming evidence for a population of postjunctional alpha 2-adrenoceptors, prazosin was similarly effective against all agonists and failed to discriminate between those with putative selectivity for alpha 1- and alpha 2-adrenoceptors. This suggests an interaction of the effects of agonists at the two alpha-adrenoceptor subtypes. 5. An attempt has been made to reconcile a number of paradoxical observations with regard to the identification of postjunctional alpha 2-adrenoceptors in vitro, and it is suggested that in many of the isolated blood vessels presently available for examination both subtypes reside on the same smooth muscle cell. The pharmacological consequences of multiple subtypes of receptors mediating the same response is considered.

Adrenergic alpha-Agonists↗
PubMed1988

An attempt at selective protection from phenoxybenzamine of postjunctional alpha-adrenoceptor subtypes mediating contractions to noradrenaline in the rabbit isolated saphenous vein.

1. An attempt has been made, with the irreversible alpha-adrenoceptor antagonist phenoxybenzamine, to find the conditions under which postjunctional alpha 1-adrenoceptors in the rabbit isolated saphenous vein can be inactivated, such that postjunctional alpha 2-adrenoceptors can be studied in isolation. 2. Following exposure to various concentrations of phenoxybenzamine, no evidence was found for a selective inactivation of the postjunctional population of alpha 1-adrenoceptors: the "rauwolscine-resistant' (alpha 1-) and the "rauwolscine-sensitive' (alpha 2-) responses to (--)-noradrenaline were similarly affected. 3. However, in "receptor protection' experiments following exposure to a combination of phenoxybenzamine and the selective alpha 2-adrenoceptor antagonist rauwolscine, the remaining response to (--)-noradrenaline appeared to be mediated by a single population of postjunctional alpha 2-adrenoceptors: the response was insensitive to prazosin and rauwolscine was more potent than corynanthine. 4. Partial isolation of the alpha 1-adrenoceptor population was attempted by pre-exposure of the preparation to a combination of phenoxybenzamine and a selective alpha 1-adrenoceptor antagonist, i.e. prazosin or YM-12617. Following receptor protection, the inhibition produced by "selective' concentrations of either of these alpha 1-adrenoceptor antagonists were not significantly different from that observed in control preparations (no phenoxybenzamine). However, the selective alpha 2-adrenoceptor antagonists rauwolscine and CH-38083 were still able to inhibit part of the remaining responses to NA. This is interpreted as indicating that, in addition to protecting the putative postjunctional alpha 1-adrenoceptors, these procedures fail to produce complete inactivation of postjunctional alpha 2-adrenoceptors. 5. It is concluded that, although phenoxybenzamine appeared to be non-selective for the two populations of postjunctional alpha-adrenoceptors in the rabbit isolated saphenous vein, inclusion of a "selective' concentration of a competitive antagonist during the inactivation period results in differing degrees of functional protection of each subtype. Pharmacological isolation was possible for alpha 2-adrenoceptors but not convincingly for alpha 1-adrenoceptors.

Adrenergic alpha-Antagonists↗
PubMed1987

A comparison of the ability of various alpha-adrenoreceptor agonists to induce EGTA-resistant contractions of rat aorta.

Phenylephrine (PE) and Guanfacine (GU) produced maximum contractions of rat isolated aorta which were 96.8 +/- 1.3% and 96.0 +/- 2.8% respectively of the maximum responses induced by noradrenaline (NA). The responses produced by maximum concentrations of NA following 2 min incubation of the preparations with 3.0 mM EGTA were 38.1 +/- 1.2% of the maxima achieved in normal Krebs. PE produced maximum EGTA-resistant responses which were significantly less than those seen with NA; GU produced EGTA-resistant responses which were significantly less than those to PE. The concentration response curves to NA and PE were shifted to the right by incubation with EGTA. The curve for PE was shifted by a significantly greater degree than that for NA. Amidephrine, UK-14,304 and St-587 produced only nominal EGTA-resistant responses even though one of these (UK-14,304) produced contractions in normal Krebs which were almost 70% of the maximum achieved by NA. The log dose ratio for all agonists (except amidephrine) were similar following the addition of 5 nM prazosin. Amidephrine had no effect in the presence of this concentration of prazosin. It is concluded that all agonists tested were acting on alpha 1-adrenoreceptors. Prazosin (5 nM) but not corynanthine (2.5 microM) slowed the rate of rise of contraction of all agonists tested. It is proposed that the rate of rise of agonist/receptor combinations is an important determinant of alpha-adrenoreceptor agonist induced EGTA-resistant responses in rat aorta.

Adrenergic alpha-Agonists↗
PubMed1987

Methylation of specific cytosine residues enhances simian virus 40 T-antigen binding to origin region DNA.

Specific binding of simian virus 40 large T antigen to origin region DNA requires the interaction of T antigen with multiples of a consensus recognition pentanucleotide sequence (5'-G[T]-A[G]-G-G-C-3'). To assess the interaction of T antigen with cytosine residues in the recognition sequences, bacterial methylases were used to methylate simian virus 40 form I DNA in vitro at specific cytosine residues. Methylation of a subset of the cytosine residues in the pentanucleotide sequences resulted in enhanced binding of T antigen to origin region DNA. Enhanced binding to the methylated pentanucleotides indicates that the methyl groups introduced on this subset of pentanucleotide cytosine residues could not have sterically interfered with the interaction of T antigen with the recognition sequences. This lack of steric interference suggests that T antigen does not make close contact in the major groove with these particular cytosine residues during normal binding.

5-Methylcytosine↗
PubMed1985

Monomers through trimers of large tumor antigen bind in region I and monomers through tetramers bind in region II of simian virus 40 origin of replication DNA as stable structures in solution.

Large tumor (T) antigen and its bound multimeric states are positioned by scanning transmission electron microscopy (STEM) within a few base pairs at control sequences of the simian virus 40 DNA origin of replication region. Proximal and distal edge positions for each multimer group match the end positions of previously mapped fragments protected from DNase cleavage. Since chance correspondence is shown to be extremely unlikely, STEM mass measurements, obtained concurrently with STEM map positions, indicate that the DNase fragments arise from bound monomers, dimers, trimers, and tetramers in binding region II and monomers, dimers, and trimers in binding region I. Simultaneous binding of seven monomer-equivalent masses is observed, three in region I and four in region II, with an ordered and interpretable mass distribution in the plane of the foil. Although this observation does not prove that the six G-A-G-G-C and one T-A-G-G-C sequences, similarly distributed, function as recognition sequences for T-antigen monomer, it provides strong support for such a model. The stable existence in solution of low-and intermediate-mass structures, observed at lower T-antigen concentrations, suggests a role as assembly intermediates.

Antigens, Polyomavirus Transforming↗
PubMed1985

Perfusion with calcium free solution potentiates prazosin blockade of noradrenaline induced pressor responses in the mesenteric bed of the rat.

Dose response curves have been constructed from pressor responses to bolus injections of noradrenaline (NA) in the perfused mesenteric bed of the rat. Prazosin (1.0-50 nM) caused a shift to the right of these dose response curves and significantly depressed the maximum obtainable response without any significant change in slope, whereas corynanthine exhibited classical competitive antagonism. When perfused with calcium-free solution, the pressor responses to NA were of shorter duration and the maximum obtainable response was reduced by 26.9 +/- 3.1%. When perfused with calcium-free solution the antagonistic effect of corynanthine was unchanged but that of prazosin was enhanced such that 5.0 nM of prazosin now caused a much greater depression of the maximum NA-induced pressor responses and a marked reduction in slope of the dose response curve. Corynanthine (10 microM) was able to reverse these antagonistic effects of prazosin. These observations are consistent with the suggestion that prazosin selectively antagonizes NA-induced calcium release.

Animals↗
PubMed1985

Origin binding by a 100,000-dalton super-T antigen from SVT2 cells.

The SVT2 line of simian virus 40-transformed mouse cells expresses little or no wild-type-size A protein (T antigen). Instead, a variant form is produced in these cells that is larger than normal-size A protein. This variant form has an Mr of 100,000 (100K super-T antigen) and is found primarily in complexes with the host-cell-coded p53 protein. Binding of the 100K super-T antigen to simian virus 40 origin region DNA was assayed by immunoprecipitation of super-T antigen-DNA complexes and then digestion with DNase I. DNA sequences associated with super-T antigen were protected from digestion and retained in the immune complex, while unprotected sequences were digested and released. The 100K super-T antigen efficiently protects DNA sequences in the previously defined regions I and II (P. Tegtmeyer, B. A. Lewton, A. L. DeLucia, V. G. Wilson, and K. Ryder, J. Virol. 46:151-161, 1983). Within region II (the origin of replication), the pattern and size of protected fragments are identical for super-T antigen and purified wild-type A protein. Thus, even though super-T antigen is larger than wild-type A protein, both must bind with the same alignment on origin DNA. Furthermore, complexes between the host-cell-coded p53 protein and the 100K super-T antigen also retain the ability to bind in regions I and II.

Antigens, Polyomavirus Transforming↗
PubMed1983

Non-competitive antagonism of the alpha-adrenoceptor-mediated fast component of contraction of rat aorta, by doxazosin and prazosin.

alpha-Adrenoceptor antagonists have been compared for their effects on dose-response curves of fast and slow components of contraction of the rat aorta to noradrenaline (NA). All agents caused a competitive antagonism of the slow component of contraction to NA. The order of potency was: prazosin greater than WB4101 = doxazosin greater than tiodazosin greater than phentolamine greater than corynanthine greater than trimazosin greater than rauwolscine. For the fast component, doxazosin, prazosin, tiodazosin and WB4101 caused some depression of the maximum response. Doxazosin (25 nM) and prazosin (25 nM) produced a complete and unsurmountable antagonism of the maximum fast component. Phentolamine, corynanthine, trimazosin and rauwolscine all competitively antagonized the fast component. The degree of antagonism of the fast component by prazosin and its analogues appeared to be directly related to the potency of individual agents for the slow component. WB4101, which was equipotent with doxazosin and more potent than tiodazosin was less effective than either in reducing the fast component. The antagonism of the fast component by prazosin or doxazosin was easily reversed by washing and prevented by phentolamine (2.5 microM). Neither prazosin nor doxazosin in concentrations of up to 2.5 microM has any effect on contractions of the aorta to 5-hydroxytryptamine (5-HT, 0.25-250 microM) or caffeine (20mM). It is concluded that the ability of some alpha-adrenoceptor antagonists to produce a non-competitive antagonism of the fast component of contraction is (a) dependent upon blockade of alpha-adrenoceptors; (b) unrelated to selectivity for alpha 1-adrenoceptors; (c) related to potency and structure. 8 EGTA (3.0 mM) caused a selective suppression of the slow component of contraction to NA. Both doxazosin and prazosin caused a non-competitive antagonism of EGTA-resistant contractions to NA whereas corynanthine showed competitive antagonism. These observations, together with those above imply that prazosin and doxazosin non-competitively antagonize alpha-adrenoceptorinduced release of calcium in the rat aorta, but competitively antagonize alpha-adrenoceptor-induced calcium entry.

Adrenergic alpha-Antagonists↗
PubMed1983

Topography of simian virus 40 A protein-DNA complexes: arrangement of protein bound to the origin of replication.

DNA binding regions I, II, and III at the origin of replication have different arrangements of A protein (T antigen) recognition pentanucleotides. The A protein also protects each region from DNase in distinctly different patterns. Footprint and fragment assays led to the following conclusions: (i) in some cases a single recognition pentanucleotide is sufficient to direct the binding and accurate alignment of A protein on DNA; (ii) the A protein binds within isolated region I or II in a sequential process leading to multiple overlapping areas of DNase protection within each region; and (iii) the 23-base pair span of recognition sequences in region II allows binding and protection of a longer length of DNA than the 23-base pair span in region I. We propose a model of protein binding that addresses the problem of variations in the arrangement of pentanucleotides in regions I and II and explains the observed DNase protection patterns. The central feature of the model requires each protomer of A protein to bind to a pentanucleotide in a unique direction. The resulting orientation of protein would protect more DNA at the 5' end of the 5'-GAGGC-3' recognition sequence than at the 3' end. The arrangement of multiple protomers at the origin of simian virus 40 replication is discussed.

Antigens, Viral↗
PubMed1982

Changes in DNA binding by purified simian RNA polymerase II under transcribing and nontranscribing conditions.

The interaction of RNA polymerase II from African Green Monkey liver tissue with SV40 DNA was examined by a DNAase protection technique. In the absence of nucleoside triphosphates, simian polymerase binds to nicked, linear SV40 DNA and protects 30 bp of binary complex DNA from DNAase I digestion. With the addition of nucleoside triphosphates to initiate transcription, polymerase protects 40 bp of the ternary complex DNA from DNAase I. Thus, a conformational change in either the polymerase, the DNA, or both occurs during the transition from binary to ternary complex, and this altered conformation allows a larger protection of template DNA. Similar results were seen with Escherichia coli RNA polymerase holoenzyme on SV40 DNA.

Animals↗
PubMed1982

DNA binding properties of simian virus 40 temperature-sensitive A proteins.

Wild-type simian virus 40 A protein (large T antigen) bound to three tandem regions of simian virus 40 DNA. The binding regions were defined by the ability of A protein to protect simian virus 40 DNA from digestion with limited (footprint assay) or excess (fragment assay) amounts of DNase I. At low concentrations, protein first bound to region I, which maps 30 to 45 base pairs to the early side of the origin of replication. At higher concentrations, A protein also protected region II and then region III. Region II spanned approximately 65 base pairs and corresponded in location to the functional origin of replication that contains a unique BglI site along with an adjacent adenine-thymine-rich region. Region III was adjacent to the late boundary of region II, but its distal limit was not well defined. Twelve distinct temperature-sensitive (ts) A proteins were purified and examined for their ability to bind in regions I to III. Three classes of tsA protein were defined on the basis of thermal stability. Class I tsA protein displayed wild-type binding either with or without a heat shock. Unheated class II tsA protein exhibited wild-type binding, but after a heat shock bound very poorly to the origin of replication. Class III tsA protein was defective in its binding even without a heat shock and only protected region I. Classes II and III were coded by mutants mapping in two distinct regions of the genome. For all of the tsA proteins examined, there was a positive correlation between the thermolability of origin binding in vitro and the temperature sensitivity of these mutants for DNA replication and transcriptional autoregulation in vivo. This correlation adds support to the essential role of origin binding by A protein in viral DNA replication and early transcription repression.

Antigens, Viral↗
PubMed1980

The NH2-terminal sequence of a precursor form of the arabinose binding protein.

Cell-free arabinose binding protein (ABP) was synthesized using a mRNA-directed Escherichia coli S30 translation system. The source of the mRNA was a total cellular RNA extract from cultures of E. coli B/r ara A 39, induced for ABP production. Purification of in vitro ABP was effected by affinity chromatography on a column of purified anti-ABP coupled to Sepharose 4B, followed by Sephadex G-75 chromatography in 9% formic acid. The purified in vitro ABP was found to have a molecular weight approximately 3000 greater than native ABP. Comparison of the CNBr peptide fragments of native and in vitro ABP demonstrated an NH2-terminal extension of 23 amino acids not present in native ABP. The identities of 20 of the residues in the extension were established, and the characteristics of this region resemble the features proposed for signal sequences that function in protein secretion.

Amino Acid Sequence↗