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V Pliska

Publications and source records attributed to V Pliska.

At least 37 records · Page 2Linked to original sources
PubMed1991

Antagonists as "affinity probes" for peptide hormone receptors: QSAR studies on oxytocin receptor in the rat myometrium.

The use of competitive antagonists in receptor investigations has been based mainly on empirically established abilities to suppress biological effects of certain agonists. This information serves primarily for classification of receptors according to ligand specificities. Methods of quantitative structure-activity analysis can extend their use for investigations of preference substituent in the desired position, estimates of ligand-receptor affinities, etc., when a set of antagonists differing solely in the substituents in that position and characterized by their pA2 values, is available. In the case of a multiple substitution, contributions of single substituents on individual positions can be estimated by the Free-Wilson method and then subjected to correlation analysis. The approach is demonstrated on a group of oxytocin analogues acting as uterotonic inhibitors of oxytocin; the "intramolecular force" descriptors are used for correlation analysis.

Angiotensin Receptor Antagonists↗
PubMed1991

Revised radioreceptor assay for beta 2-adrenoceptors expressed on peripheral mononuclear leukocytes.

Peripheral mononuclear leukocytes (pMNL) bear a population of beta 2-adrenoceptors. Radioreceptor assays with (-)-125Iodocyanopindolol (125I-CYP) are often used to determine the expression of these hormone receptors under physiological and pathological conditions. Doubts on the occurrence of just one class of binding sites as well as the availability of new laboratory equipment prompted us to revise the procedure employed for investigation of these receptors. pMNL were harvested from venous human blood by density centrifugation with LymphopaqueR, LymphoprepR, or FicollR yielding immunologically distinct pMNL fractions. Receptor binding assays were performed semi-automatically with 125I-CYP in the range from 0.6-600 pmol/l. Analysis of the data (modified affinity spectra, Scatchard plot) revealed two classes of binding sites (high- and low affinity binding). The binding isotherms were sigmoidal in the concentration range from 0.6-3.0 pmol/l. Parameters estimated for the high affinity binding site may vary by a factor of 10, depending on the mathematical model employed.

Humans↗
PubMed1990

Multiple [3H]-oxytocin binding sites in rat myometrial plasma membranes.

The affinity spectrum method has been used to analyse binding isotherms for [3H]-oxytocin to rat myometrial plasma membranes. Three populations of binding sites with dissociation constants (Kd) of 0.6-1.5 x 10(-9), 0.4-1.0 x 10(-7) and 7 x 10(-6) mol/l were identified and their existence verified by cluster analysis based on similarities between Kd, binding capacity and Hill coefficient. When experimental values were compared to theoretical curves constructed using the estimated binding parameters, good fits were obtained. Binding parameters obtained by this method were not influenced by the presence of GTP gamma S (guanosine-5'-O-(3-thiotriphosphate) in the incubation medium. The binding parameters agree reasonably well with those found in uterine cells, they support the existence of a medium affinity site and may allow for an explanation of some of the discrepancies between binding and response in this system.

Animals↗
PubMed1988

Binding of the delta endotoxin from Bacillus thuringiensis to brush-border membrane vesicles of the cabbage butterfly (Pieris brassicae).

The insecticidal delta endotoxin of Bacillus thuringiensis was labeled with iodine-125. Brush-border membrane vesicles, prepared from the midgut epithelium of Pieris brassicae larvae, known to be highly susceptible to the toxin, and from a non-target tissue: the small intestine of rat, were examined for binding of 125I-toxin. The toxin was bound specifically only to insect vesicles. Its binding to the insect membrane system was competitively inhibited by 127I-toxin and non-iodinated toxin, whereas the binding of the 125I-toxin to the mammalian membrane system was not affected by unlabeled toxin. Vesicles of P. brassicae possess two individual binding-site populations for iodinated toxin with dissociation constants of 46 nM and 490 nM. The Hill coefficients of both sites were approximately 1 and the binding capacities were 0.2 pmol and 30 pmol/mg vesicle protein for the high and the low-affinity sites respectively. The estimation of the dissociation constant for non-iodinated toxin, using a competition experiment, revealed only one binding-site population which possessed a dissociation constant of 235 nM. It is concluded that this is the binding site for the native toxin. This site was sensitive towards treatment with proteases or mixed glycosidases. It is suggested that it is a protein or a glycoprotein.

Animals↗
PubMed1988

Structural requirements of the oxytocin receptor in rat uterus. Free-Wilson analysis in a series of competitive oxytocin inhibitors.

Published and newly calculated pA2-values of 147 neurohypophyseal hormone analogues (7 positions varied) acting as inhibitors of oxytocin on isolated rat uterus in vitro have been subjected to fractionation according to the method by Free and Wilson which was slightly modified for this purpose. The computation was carried out in several steps. After each step, substances with outlying pA2-values were eliminated. The reduced group containing 73-79% of the original substances displayed a high degree of additivity of side chain contributions (SCC). This group seems to follow the "participation" rule as formulated by Free and Wilson. Analysis of the group of eliminated substances and of the resulting SCC-spectrum (level diagram) enabled us to draw some conclusions concerning the structural requirements of receptor binding: i) The intact ring structure is necessary for the peptide-receptor interaction: linear peptides or peptides with an extended ring are always outliers; ii) Carba analogues (substitution with CH2 in the disulfide ring) display better affinities than peptides with an S-S ring; D-Arg8 substitution decreases the binding affinity; iii) Considerably better additivity is achieved when peptides are divided into subgroups with vasopressin-like and oxytocin-like features; populations of receptors more specific for vasopressin and for oxytocin, respectively, can be assumed. Estimates of the "true" receptor-peptide dissociation constants can be obtained by summation of the corresponding SCC's in each investigated position. The value obtained for oxytocin is identical with the medium affinity binding site on myometrial cells, and not with the high affinity site. A nonlinear relationship exists between SCC's computed from pA2-values for magnesium-free and magnesium-containing (0.5 mM) media but no evidence speaks in favor of a Mg-potentiating effect on receptor binding.

Amino Acid Sequence↗
PubMed1988

Amino acid side chain parameters for correlation studies in biology and pharmacology.

Fifteen physicochemical descriptors of side chains of the 20 natural and of 26 non-coded amino acids are compiled and simple methods for their evaluation described. The relevance of these parameters to account for hydrophobic, steric, and electric properties of the side chains is assessed and their intercorrelation analyzed. It is shown that three principal components, one steric, one bulk, and one electric (electronic), account for 66% of the total variance in the available set. These parameters may prove to be useful for correlation studies in series of bioactive peptide analogues.

Amino Acid Sequence↗
PubMed1988

Antihaemophilic effect of vasopressin, deamino-(D-arginine8)-vasopressin and adrenaline in sheep: proposal for an in vivo assay system.

Female sheep were used to assay antihaemophilic (factor VIII enhancing) activity of arginine vasopressin, deamino-(D-arginine8)-vasopressin (DDAVP) and adrenaline. The time course of the response was biphasic, two surges of factor VIII being observed. DDAVP was found to be the most potent of the substances investigated. Its optimal dose was 1 microgram kg-1 body wt (i.v.). It is suggested that a similar procedure can be employed to search for new peptides with anti-haemophilic action.

Animals↗
PubMed1988

Pharmacological approaches to the identification and classification of myometrial oxytocin receptors.

Three binding sites have been recently reported on the rat, calf and sheep myometrial cells, with dissociation constants (Kd) roughly 10(-9), 10(-7) and 10(-5) mol/l. Oxytocin receptor for the uterotonic response in vitro was identified pharmacologically: 1) The analysis of dose-response curves has been based on a partial irreversible inhibition of the receptor on isolated rat uterus by the method of Furchgott and Bursztyn, and by the newly suggested plotting of Kd vs. maximal response for an increasing degree of irreversible inhibition. 2) pA2- values (reflecting Kd) of structural analogues of oxytocin acting as competitive inhibitors of the parent hormone have been analysed according to Free and Wilson. Contribution of side chains in individual positions of the nonapeptide chain were computed, tested on additivity and then used for back-computation of a Kd for oxytocin. Results of all experiments reveal a Kd for oxytocin receptor (rat uterus in vitro) of 2 x 10(-7) mol/l. Possible endocrine functions of the high and low affinity sites have not been clarified as yet.

Animals↗
PubMed1987

Renin inhibitors. Free-Wilson and correlation analysis of the inhibitory potency of a series of pepstatin analogues on plasma renin.

Free-Wilson and correlation analysis were combined to study a series of 34 pepstatin analogues in which mainly position 2 was varied. A statistically highly significant correlation was found between the inhibitory activity of the analogues on an enriched plasma renin preparation and structural parameters of the amino acid side chain in position 2. The crucial parameters were found to be the NMR chemical shift of the alpha-carbon, the localized electrical (inductive) effect, and the van der Waals radius related steric parameter, which demonstrated the dominating influence of electronic inductive effects compared to steric bulk. The model gives insight into the structural requirements for effective inhibition and suggests the histidine-2 derivative, a positive outlier in this series, as a lead compound for further structure-activity studies.

Oligopeptides↗
PubMed1986

Binding of oxytocin to uterine cells in vitro. Occurrence of several binding site populations and reidentification of oxytocin receptors.

Myometrial and endometrial cells of sheep, rat, and calf in monolayer cell culture display at least three populations of binding sites for oxytocin, with dissociation constants (Kd) of approximately 5 X 10(-9), 4 X 10(-7), and greater than 10(-5) mol/liter, respectively. Binding of the tritium-labeled oxytocin (concentration range, 10(-11) to 5 X 10(-4) M) to the first two sites is displaceable by cold oxytocin. The ratio of binding capacities of the high to medium affinity site appears to average 1:18. Dissociation rate constants for these sites (22 degrees C) are roughly 10(-4) and 2 X 10(-3) s-1, respectively. The capacity of the low affinity site varies in individual cell preparations and is between 5 and 66 times that of the medium affinity site. The low affinity binding sites may not be fully saturable and may follow a nonasymptotic binding isotherm. Logarithms of Kd and binding capacity for individual binding sites are linearly correlated. The coexistence of the three sites was also proven by cluster analysis based on similarities between Kd, binding capacity, and Hill coefficient. Only minor systematic species and cell type differences occur in these properties. The value of Kd for the oxytocin receptor in rat myometrium, derived recently from a stepwise irreversible inhibition of uterotonic response to oxytocin, is close to 2.5 X 10(-7) mol/liter. Additional pharmacological data (pA2 values of structural analogues of oxytocin acting as competitive inhibitors) also reveal a Kd value of 3 X 10(-7). It is, therefore, concluded that the receptors for oxytocin in rat myometrium are identical with the medium affinity site.

Animals↗
PubMed1984

Investigation of drug-receptor interactions by means of irreversible receptor inhibitors: binding of oxytocin and angiotensin II to their receptors in rat uterus.

A stimulus-response coupling model in which individual steps follow hyperbolic or Hill-type laws has been employed to mimic phenomena associated with irreversible receptor inhibition (receptor reserve) in a responding biological system. Two methods for computation of ligand-receptor dissociation constant (KA) have been derived from this model: 1) The relation between pD2 and maximal attainable response allows a rough estimate of KA; 2) A generalization of the earlier Furchgott-Bursztyn procedure employing equipotent doses for noninhibited and partially inhibited systems, has been achieved by introduction of Hill equation into the model. Applied to oxytocin and angiotensin II receptors in rat uterus, these pharmacological methods indicate rather low affinity of the two receptors for the respective peptides (around 2 X 10(-8) for angiotensin II and 2 X 10(-7) mol/l for oxytocin), in case of oxytocin much lower than values reported from binding studies. Apparently, several binding sites are present on the target tissue cells from which the methods based on cellular response can pick up those corresponding to the receptors. Biophysical methods are lacking this ability. Single pD2 values in noninhibited systems cannot themselves deliver any relevant information about receptor binding.

Angiotensin II↗
PubMed1983

Displacement reactions employing heterologous tracer ligands in peptide receptor studies: a review.

Heterologous tracer ligands used in displacement studies with peptide-receptor systems may become unsuitable to these aims for several reasons. (1) The forms of binding isotherms for the tracer and for the ligand under investigation are different. The Schild plot and similar schemes are then not applicable. Possible modifications of the computational methods are indicated. (2) The rate of dissociation from the receptor is slowed, until almost irreversible. In such cases, there is no chance for displacement studies. (3) Large discrepancy in rate constants, or dramatically different distribution coefficients between binding system and water, for the two ligands mimic irreversible binding to receptors in a pharmacological experiment. Adjustment of ligand concentrations (control of association rate) may help in some instances.

Adenylyl Cyclases↗
PubMed1982

Comparison of radioimmunoassay, chemical assay (HPLC) and bioassay for arginine vasopressin in synthetic standards and posterior pituitary tissue.

Radioimmunoassay and chemical assay (high performance liquid chromatography (HPLC) with fluorescence detection) for arginine vasopressin (AVP) in purified synthetic preparations and in posterior lobe tissue samples (ox and rat) yielded essentially identical values. In tissue samples from the neurohypophysis, the reproducibility of the former method was roughly twice as good. The routinely used blood pressure bioassay was very poorly reproducible and yielded values deviating from the two ther methods. In all three assays, the coefficient of variation was roughly five times higher in tissue samples than in synthetic preparations. It is suggested that a chemical rather than a biological assay is used for standardization of AVP for radioimmunoassay. Large differences were found in the quality of AVP preparations potentially usable as standards and tracers (after iodination) for radioimmunoassay. All commercial preparations should therefore be checked for their AVP and impurity content by high performance liquid chromatography.

Amino Acids↗
PubMed1981

Identification of the pituicytes as astroglial cells by indirect immunofluorescence-staining for the glial fibrillary acidic protein.

Glia cells of rat neural lobes (pituicytes) were stained in thin sections (6 micrometers) by the indirect immunofluorescence technique for the glial fibrillary acidic protein (GFA), the S-100 protein and fibronectin. The positive strong GFA-staining of the pituicytes demonstrates their astroglial character. Fibronectin was located along the blood capillaries. After six days of implantation of the neural lobes under the kidney capsule of an acceptor rat, the stained fibronectin was augmented and present in a fibrillar network scattered over the tissue; the GFA-staining remained positive, however. The astroglial character of pituicytes was apparently retained in the implantation conditions, whereas neurosecretory axons had already disappeared. No S-100 protein could be unambiguously detected in the glia cells with the antibody employed.

Animals↗
PubMed1980

Antidiuretic agonism and antagonism of some O-alkylated analogues of vasopressin containing 2-O-alkylated tyrosine.

A series of 2-O-alkylated tyrosine analogues of lysine-vasopressin and desamino-lysine and arginine-vasopressin were synthesized and tested for antidiuretic activity in the water-loaded anaesthetized rat. The analogues displayed only weak antidiuretic activities. When they were infused in the rats together with lysine vasopressin it was found that 1-deamino-[2-O-ethyltyrosine]-lysine-vasopressin inhibited the vasopressin-induced antidiuretic response. The antagonistic properties were further evaluated in long-term experiments on conscious non-hydrated rats with implanted minipumps. The analogues inhibited the vasopressin-induced antidiuresis at antagonist:agonist ratios of 0.5 and 1.0.

Alkylation↗
PubMed1980

Long term stability of lysine vasopressin and of specifically tritiated lysine vasopressin in weakly acidic aqueous solutions.

Lysine vasopressin tritiated at meta position of tyrosine (1.9 Ci/mmole) decomposes during a long storage period, mainly as a result of radiolysis. The loss of specific activity by isotopic exchange with water is slow. The nonlabelled peptide undergoes only very minute decomposition (polymerization). Specific radioactivity declines with a half life of 47.4 months.

Animals↗
PubMed1980

Effect of O-alkylated analogues of lysine vasopressin on adenylate cyclase of pig kidney membranes.

O-alkylated analogues (ethyl, propyl, butyl, tert.-butyl) of lysine vasopressin (LVP) and deamino-LVP are partial agonists to LVP in their effect upon activation of adenylate cyclase in porcine kidney membranes. Emax and pD2 values are linearly dependent and both of them are inversely proportional to the overall hydrophobicity of the peptides, expressed in terms of capacity factors in reversed phase high performance liquid chromatography. It is suggested that the increasing hydrophobicity augments the tendency to either a "wrong way" binding, or to a side-side interaction of several peptide ligands bound to a multi-subsite receptor or both. The data circumstantially indicate that the relation between the peptide-receptor interaction and cyclase activation is not a linear one.

Adenylyl Cyclases↗