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Biomedical subjects

S Dion

Publications and source records attributed to S Dion.

At least 37 records · Page 2Linked to original sources
PubMed1989

Receptors for substance P and related neurokinins.

The most widely used smooth muscle preparations for neurokinin bioassays have been critically analyzed in order to determine whether neurokinins act directly or by the intermediary of other natural agents. Indeed, part of the contraction of the GPI in response to neurokinins appears to be mediated by acetylcholine and possibly prostaglandins. Active metabolites of the arachidonic acid cascade also intervene in the response of the HUB. Neurokinins produce relaxation of the DCA by stimulating the release of a vascular smooth muscle relaxing factor from the endothelium. In the other preparations (the RD, the RPA without endothelium and the RPV) neurokinins may act directly on the smooth muscle fibers. Neurokinins produce their biological effects by activating specific receptors. Three different receptor types, one for each mammalian neurokinin, have been identified by using four groups of natural peptide sequences and some selective agonists. The receptor for SP is particularly sensitive to SP and physalaemin and shows higher affinity for the whole natural peptides (SP, NKA) than for their C-terminal fragments. The receptor for neurokinin A is highly sensitive to NKA and eledoisin: it shows high affinity for heptapeptide fragments such as NKA4-10 and SP5-11. The receptor for NKB is sensitive to NKB and kassinin more than to the other natural peptides and their fragments. The natural peptides show however little selectivity. Synthetic analogues active on a single receptor type (selective agonists) have been used to find out whether the responses of the isolated organs are due to the activation of one or more than one receptor. It has been found that the GPI, the RD and the HUB contain all three or at least two receptors, while the DCA has only the NK1, the RPA has only the NK2 and the RPV only the NK3 type. Binding sites specific for each neurokinin have been identified in brain and peripheral organs with accurate biochemical assays, using labeled neurokinins. Competitive displacement assays have been performed with a variety of neurokinin-related peptides, and their Ki have been determined. By plotting Ki values against the ED50, estimated from biological assays, positive significant correlations have been found for the monoreceptor (DCA, RPA, RPV) but not for the multiple receptor systems (GPI, RD, HUB). This suggests that pharmacological receptors may be identical with the recognition sites which bind the labeled neurokinins. The availability of monoreceptor systems and of selective agonists opens the way for the identification of potential antagonists and accurate estimation of their affinities.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Bradykinin antagonism: differentiation between peptide antagonists and antiinflammatory agents.

Three non-steroidal antiinflammatory agents were tested for their ability to antagonize bradykinin in the rabbit jugular vein, the dog carotid artery and the guinea pig trachea. The new agents were compared with indomethacin, as well as with [Thi5,8,D-Phe7] bradykinin and [Thi6,9,D-Phe8] kallidin, two B2 receptor antagonists. The antiinflammatory agents did not alter the effects of bradykinin in the two isolated vessels while they completely blocked (like indomethacin) the relaxation induced by bradykinin in guinea pig tracheae contracted with histamine or neurokinin A. The two bradykinin antagonists significantly reduced the contractions of the rabbit jugular vein and the relaxation of the dog carotid artery (with endothelium) in response to bradykinin: these antagonists were however inactive against bradykinin in the guinea pig trachea. The data now reported suggest that B2 receptors are involved in the opposite (stimulant or inhibitor) effects of the kinins in the two isolated vessels while the relaxation of the guinea pig trachea is a prostaglandin-dependent phenomenon which does not involve the activation of B1 or B2 receptors.

Animals↗
PubMed1987

Characterization of neurokinin receptors in various isolated organs by the use of selective agonists.

The three mammalian neurokinins, substance P, neurokinin A and neurokinin B, as well as some agonists selective for their respective receptors, NK-P, NK-A and NK-B, were tested in a variety of pharmacological preparations in order to evaluate if the biological responses of the various tissues were mediated by single or multiple receptor types. Previous observations that the dog carotid artery, the rabbit pulmonary artery and the rat portal vein are selective preparations respectively for SP, NKA and NKB were confirmed in the present study by showing that only the respective selective agonists were active on these tissues. Multiple functional sites were demonstrated in intestinal tissues (guinea pig ileum, rat duodenum), which apparently contain the three neurokinin receptors. A large number of NK-P, together with some NK-A receptor sites were found in the guinea pig and rat urinary bladder. Similarly, the guinea pig trachea and the rabbit mesenteric vein contain NK-A and NK-P functional sites. Rat and rabbit vas deferens stimulated electrically respond as typical NK-A preparations, since they are almost insensitive to SP or NKB selective agonists. A mixture of NK-A and NK-B receptor sites has been shown to be present in the hamster urinary bladder: dog and human urinary bladder definitely contain NK-A receptors and the dog bladder also some NK-P functional sites.

Animals↗
PubMed1987

Receptors for substance P and neurokinins. Correlation between binding and biological activities.

The biological activities of neurokinin-related peptides were compared with their binding affinities measured in various laboratories. A positive significant correlation was demonstrated between the relaxation of the dog carotid artery and the binding of Bolton-Hunter [125I]substance P to rat brain synaptosomes, the contractions of the rat duodenum and the rabbit pulmonary artery and the binding of Bolton-Hunter [125I]neurokinin A to duodenum smooth muscle plasma membranes, and the contraction of the rat portal vein and the binding of [125I]Bolton-Hunter NH-senktide to rat cerebral cortex membranes.

Animals↗
PubMed1987

Specific agonists for neurokinin B receptors.

A series of analogues of the partial sequence NKB-(4-10) (H-Asp-Phe-Phe-Val-Gly-Leu-Met.NH2) was prepared in an attempt to identify selective agonists for the neurokinin B receptor type. The compounds were tested in the dog carotid artery, the rabbit pulmonary artery and the rat portal vein to evaluate their affinity for the receptors of substance P, neurokinin A and neurokinin B respectively. It has been shown that the replacement of Val7 with MePhe increased significantly the affinity of NKB-(4-10) for the neurokinin B receptor and confered marked selectivity. [MePhe7]NKB-(4-10) was practically inactive as stimulant of the receptor for NKA and was a weak agonist on the receptor for SP. Such significant changes in the pharmacological spectrum of [MePhe7]NKB-(4-10) cannot be attributed to protection from metabolism and appear to be due to changes in the peptide conformation.

Animals↗
PubMed1987

The rat isolated portal vein: a preparation sensitive to neurokinins, particularly neurokinin B.

The rat isolated portal vein is a pharmacological preparation more sensitive to neurokinin B than to any other neurokinin or tachykinin. The preparation is more sensitive to C-terminal partial sequences of substance P (SP) particularly SP-(6-11) than to the whole undecapeptide. The order of potency of neurokinins is as follows: neurokinin B greater than neurokinin A greater than substance P. The preparation shows high sensitivity also to kassinin and eledoisin. Comparative tests performed with strips of the rat portal vein suspended in a microbath under continuous perfusion (system 1) or in ordinary baths for isolated smooth muscles (system 2) have given similar results and have shown that the myotropic effect of neurokinin B is not modified by a variety of antagonists of endogenous agents as well as by inhibitors of the arachidonic acid cascade. The present results suggest that neurokinin B contracts the rat portal vein by activating specific receptors, presumably located on the smooth muscle membrane, different from those of biologically active amines and peptides which are active stimulants of the vein. Neurokinin B is ten times more active than neurokinin A and at least 100 times more than substance P. Such an order of potency of agonists suggests the existence of a new neurokinin receptor type, particularly sensitive to neurokinin B.

Animals↗
PubMed1987

Pharmacological receptors for substance P and neurokinins.

The three neurokinins identified in mammals, substance P, neurokinin A and neurokinin B, as well as their C-terminal biologically active fragments, have been used to characterize the responses of a variety of isolated organs. Three preparations selective either for substance P (the dog carotid artery), or for neurokinin A (the rabbit pulmonary artery) or for neurokinin B (the rat portal vein) are described. A neurokinin receptor classification is attempted using the neurokinins and their fragments to determine the order of potency of agonists. Three receptor subtypes have been identified: the NK-P, on which substance P (SP) is more active than neurokinin A (NKA) and neurokinin B (NKB), and the neurokinins are more active than their respective fragments; the NK-A on which NKA greater than NKB greater than SP, and some NKA fragments are more discriminative than their precursor; the NK-B on which NKB greater than NKA greater than SP, and fragments of NKB are less active than their precursor. Among the peptides studied, some potent compounds have been identified that could provide selective receptor ligands.

Animals↗
PubMed1987

Selective agonists for substance P and neurokinin receptors.

A series of neurokinin analogues and fragments have been prepared in an attempt to identify selective agonists for NK-P, NK-A and NK-B receptors. The compounds have been tested on the dog carotid artery (NK-P receptor system), the rabbit pulmonary artery (NK-A) and the rat portal vein (NK-B). C-terminal substituted analogues of the three neurokinins have provided indication that NK-P receptor selectivity is improved by the oxidation of methionine to Met(O2), while selectivity for NK-A is favoured by replacing Met with NIe. Selectivity for NK-P receptors is further improved by the replacement of Gly9 with Sar. Selectivity and affinity for NK-B receptors is markedly increased when Val7 is replaced with MePhe in both the fragment NKB (4-10) and NKB. The results of the present study indicate that a) [Sar9,Met(O2)11]SP is a potent and selective agonist for the NK-P receptors of the dog carotid artery; b) [MePhe7]NKB is a very potent and selective stimulant of receptors for neurokinin B and c) [Nle10]NKA (4-10) is a promising compound, showing some selectivity for NK-A receptor; further modifications are however needed to improve its affinity.

Animals↗
PubMed1987

Interaction of tachykinins with their receptors studied with cyclic analogues of substance P and neurokinin B.

The activities of two groups of cyclic agonists of substance P (SP) have been studied. The disulfide bridge constraints have been designed on the basis of conformational studies on SP and physalaemin indicating an alpha-helical structure for the core of these two tachykinins (group I) and a folding of the C-terminal carboxamide towards the side chains of the glutamines 5 and 6 (group II). Only peptides simulating the alpha-helix present substantial potencies. [Cys3,6]SP is as active as SP in inhibiting 125I-labeled Bolton and Hunter SP-specific binding on rat brain synaptosomes and on dog carotid bioassay, two assays specific for the neurokinin 1 receptor. Moreover, [Cys3,6]SP is as potent as neurokinin B in inhibiting 125I-labeled Bolton and Hunter eledoisin-specific binding on rat cortical synaptosomes as well as in stimulating rat portal vein, two tests specific for the neurokinin 3 receptor. Interestingly, in contrast to neurokinin B, [Cys3,6]SP is a weak agonist of the neurokinin 2 receptor subtype, as evidenced by its binding potency in inhibiting 3H-labeled neurokinin A-specific binding on rat duodenum and in inducing the contractions of the rabbit pulmonary artery, a neurokinin 2-type bioassay. To increase the specificity of the cyclic analogue [Cys3,6]SP positions 8 and 9 were modified. [Cys3,6, Tyr8, Ala9]SP is slightly less selective than SP for the neurokinin 1 receptor subtype. [Cys2,5]neurokinin B constitutes a selective cyclic agonist for the neurokinin 3 receptor. The very weak potencies of the peptides from group II indicate that a certain degree of flexibility in the C-terminal moiety is required. Collectively, these results suggest that the neurokinin 1 and neurokinin 3 tachykinin receptors may recognize a similar three-dimensional structure of the core of the tachykinins. Different orientations of the common C-terminal tripeptide may be related to the selectivity for the different receptor subtypes.

Amino Acid Sequence↗
PubMed1987

3H-neurokinin A labels a specific tachykinin-binding site in the rat duodenal smooth muscle.

3H-Neurokinin A (3H-NKA) with high specific activity (75 Ci/mmol) was synthesized to study NKA (NK-2)-binding sites on membrane preparations of various tissues in the rat, including brain, spinal cord, duodenum, vas deferens, and ileum. The binding capacity of 3H-NKA (0.9 nM) was very low in membrane preparations of different central nervous system regions and the ileum smooth muscle (0.2-2 fmol/mg of protein). In contrast, relatively high specific binding was found in membrane suspensions of the rat duodenal smooth muscle (18 fmol/mg of protein) and the vas deferens (8 fmol/mg of protein). 3H-NKA-binding sites were further characterized on the rat duodenal smooth muscle. The specific binding of 3H-NKA was shown to be temperature dependent, saturable, reversible, and increased in parallel with the protein concentration. Scatchard analyses and Hill plots of equilibrium binding studies in the concentration range of 0.40-30 nM revealed that 3H-NKA bound to a single class of noninteracting binding sites (Bmax = 270 fmol/mg of protein, KD = 13.3 nM). Displacement of 3H-NKA with different tachykinin-related peptides gave the following rank order of potencies: NKA greater than NKA (4-10) greater than kassinin greater than eledoisin greater than NKB much greater than substance P greater than physalaemin, which suggests that the binding site labeled by 3H-NKA is different from substance P (NK-1)-and NKB (NK-3)-binding sites. The biological activities of tachykinins and related peptides were tested by measuring their contractile effects on the rat duodenum and rabbit pulmonary artery, two tissues known to be sensitive for NKA. Ki values were correlated with the EC50 obtained in biological assays. The results revealed a significant correlation (r = 0.86, p less than 0.01) between Ki and EC50 values obtained in the isolated rabbit pulmonary artery, whereas there was no significant correlation between binding affinities and biological responses on the rat duodenum (r = 0.62, p greater than 0.05).

Animals↗
PubMed1986

Conversion of kinins and their antagonists into B1 receptor activators and blockers in isolated vessels.

A carboxypeptidase inhibitor (DL-2-mercaptomethyl-3-guanidoethylthiopropranoic acid) (mergetpa) was used to block the conversion of kinins and B2 receptor antagonists into metabolites devoid of the C-terminal Arg. Experiments were carried out on rabbit isolated aortae (a B1 receptor system) or rabbit jugular veins and dog carotid arteries (two B2 receptor systems). The contractile effect of bradykinin in the rabbit aorta was significantly reduced by mergetpa while that of desArg9-BK was not modified. pA2 values of B2 receptor antagonists, [Thi5,8,D-Phe7]bradykinin and [Thi6,9,D-Phe8]kallidin were markedly reduced by mergetpa. The apparent affinity (pA2) of a B1 receptor antagonist, [Leu9]desArg10-kallidin was not affected. Carboxypeptidases inhibition did not modify the activities of bradykinin or the affinities of B2 receptor antagonists in the rabbit jugular vein and the dog carotid artery. An inhibitor of kininase II (D-3-mercapto-2-methylpropranoyl-L-proline (S,S] (captopril) reduced the contractile effects of angiotensin I in the three preparations and potentiated the stimulatory or inhibitory effects of bradykinin: captopril did not have effect on the affinities of B2 receptor antagonists and did not modify the effects of angiotensin II. Comparative experiments performed in tissues with or without endothelium gave the same results with both mergetpa and captopril. The present findings suggest that bradykinin and B2 receptor antagonists are converted by carboxypeptidases into biologically active B1 receptor agonist or antagonists. This is the reason why B2 receptor antagonists are not selective.

3-Mercaptopropionic Acid↗
PubMed1986

Different receptors are involved in the endothelium-mediated relaxation and the smooth muscle contraction of the rabbit pulmonary artery in response to substance P and related neurokinins.

Four neurokinins, substance P (SP), neurokinin A (NKA) neurokinin B (NKB) and kassinin (Kass) were used in the present study together with other peptides and nonpeptide agents to demonstrate the existence of two different neurokinin receptor types in the rabbit isolated pulmonary artery. Similar to other arterial vessels, the endothelium-dependent relaxation of the pulmonary artery in response to neurokinins is due to the activation of a SP-P receptor more sensitive to SP than to the other neurokinins. The endothelium-dependent relaxation is an indirect phenomenon, mediated by an unknown endothelial agent, similar to that released by acetylcholine. The contraction of the pulmonary artery in response to neurokinins is due to receptors of the NK-A type, particularly sensitive to NKA and NKB, and much less sensitive to SP. The contraction is a direct phenomenon, apparently not involving any of the known endogenous autacoids and neurotransmitters or metabolites of arachidonic acid. Contraction appears to be due to stimulation by the neurokinins of receptors located in the arterial smooth muscle. The results presented in this paper indicate that NK-A receptors for neurokinins (which are present in the tracheo-bronchial tree) are also to be found in pulmonary vessels and mediate contraction of arterial vascular smooth muscle, an interesting property of neurokinins.

Animals↗
PubMed1986

The actions of kinin antagonists on B1 and B2 receptor systems.

The newly discovered bradykinin antagonist [Thi5,8,D-Phe7]Bradykinin, supplied by J.-M. Stewart and three other compounds, [D-Phe7]BK, [Thi5,8,D-Phe7]Bradykinin and [Thi6,9,D-Phe8]Kallidin synthesized in our laboratory, were tested for their ability to antagonize bradykinin in four B2 receptor systems, the guinea-pig ileum, the rabbit jugular vein, the dog carotid artery and the dog urinary bladder as well as against desArg9-bradykinin in the rabbit aorta (a B1 receptor system). [D-Phe7]Bradykinin is a partial agonist, while [Thi5,8,D-Phe7]Bradykinin and [Thi6,9,D-Phe8]Kallidin are pure antagonists, the second one showing little BK-like activity on three of the four preparations. The kallidin analogue is more potent in all preparations than the bradykinin one. The two [Thi5,8,D-Phe7]BK (that supplied by J.-M. Stewart and that prepared in our laboratory) show very similar affinities in all preparations. The bradykinin analogue as well as the kallidin one are also active against desArg9-bradykinin in the rabbit aorta, at concentrations similar to those active on B2 receptor systems. The kinin antagonists are however specific for the kinins, since they do not interfere with the myotropic effects of angiotensin or substance P (SP) in the various preparations.

Animals↗