Release of histamine by neuropeptides from the perfused rat hindquarter

The release of histamine and serotonin by neuropeptides and capsaicin was measured in the isolated perfused rat hindquarter preparation. Substance P and two antagonistic peptides, [D-Pro2, D-Phe7, D-Trp9]-SP and [D-Pro2, D-Trp7,9)]-SP, release histamine, the SP(4-11) and SP(6-11) analogues did not. VIP and somatostatin released histamine and also serotonin. No amines were released by bombesin. Thus, all amine releasing peptides possessed at least two basic charges. However, the histamine releasing activity of the neuropeptides tested did not correlate with their reported ability to cause vasodilation and plasma extravasation. The SP(4-11) and SP(6-11) analogues which did not release histamine caused plasma extravasation. It is concluded that SP causes plasma extravasation by a direct action on blood vessels. Capsaicin released only serotonin but no histamine either in untreated rats and such desensitized with capsaicin as neonates. In rats desensitized with capsaicin 4 days prior to the experiment the substance P induced histamine release was as high as in untreated controls; it was, however, absent in rats desensitized with capsaicin as neonates. It is assumed that the sensitivity of mast cells to substance P is lost after degeneration of substance P containing primary sensory fibers.     

A quantitative structure-activity relationship study of some substance P-related peptides A multivariate approach using PLS and variable selection

Nine new analogues of substance P (SP) were designed using quantitative sequence-activity models based on the amino acid z-scales with PLS as the statistical method and the GOLPE procedure for variable selection. The nine SP analogues were synthesised by solid-phase peptide synthesis and tested for affinity to the NK-1 receptor from rat brain with radio receptor assay using [¹²⁵I]-Bolton-Hunter substance P as labelled ligand. All of the new substance P analogues showed high affinities, with IC₅₀ values of less than 0.8 nM. One analog, Lys-Arg-Ala-Lys-Phe-Met-Met-Phe-Phe-Gly-Leu-Let-NH₂, showed a exceptional high affinity for the NK1 receptor, with IC₅₀= 5 PM.     

Direct evidence for a release of acetylcholine from the myenteric plexus of guinea pig small intestine by substance P

Myenteric plexus-longitudinal muscle strips from guinea pig small intestine were labeled with [3H]choline while under continuous field stimulation. Release of newly synthesized [3H]acetylcholine was studied in the presence of substance P afterwards. Substance P evoked release of [3H]acetylcholine in a dose-related fashion. Both tetrodotoxin and [D-Pro2,D-Phe7,D-Trp9]substance P, a synthetic antagonist of substance P, completely blocked this release and provided evidence for a cholinergically mediated mechanism of substance P on enteric neurons.     

Interaction of neurotensin with the substance P receptor mediating histamine release from rat mast cells and the flare in human skin.

1 Substance P induced histamine release from rat peritoneal mast cells in a dose-dependent manner over the concentration range 1 to 10 microM. 2 At concentrations in the range 2.5 to 1 0 microM, neurotensin produced only about 5% release of histamine, which was substantially less than the maximum effect obtained with substance P. 3 Neurotensin, 2.5 to 10 microM produced graded inhibition of histamine release induced by substance P. The inhibitory effect of neurotensin was not seen when histamine release was induced by an antigen-antibody effect of neurotensin was not seen when histamine release was induced by an antigen-antibody reaction or by the ionophore, A 23187. Some evidence was obtained to suggest that compound 48/80 may interact with the same receptor as substance P and neurotensin. 4 [D-Arg8]neurotensin, [D-Arg9]neurotensin, xenopsin and the C-terminal octapeptide of substance P (SP4-11) all inhibited histamine release by substance P, but physalaemin did not. 5 Neurotensin inhibited the wheal and flare reactions induced by substance P in human skin. 6 [D-Trp7,9]substance P released histamine from rat mast cells and was about 12 times more potent than substance P itself. [D-Trp7,9]SP1-11 also produced wheal and flare responses in human skin, being 1.8 times more potent than substance P in the production of flare.     

Effect of thiorphan on response of the guinea-pig gallbladder to tachykinins

Tachykinins produced a concentration-related contraction of the isolated guinea-pig gallbladder, with a rank order of potency neurokinin A (NKA) greater than Arg-neurokinin B = neurokinin B (NKB) greater than substance P (SP). Only the effect of SP was potentiated by thiorphan (0.1-10 microM). A significant enhancement of the response to SP was also produced by captopril (1 microM). [Nle10]NKA-(4-10) and [beta-Ala8]NKA-(4-10), selective NK-2 receptor agonists, were active, whereas [Pro9]SP sulfone (selective NK-1 agonist) was almost ineffective. [MePhe7]NKB (selective NK-3 agonist) had some activity but only at high concentrations. Septide was almost ineffective and DiMeC7 had an action comparable to that of [MePhe7]NKB. None of the effects induced by these synthetic tachykinin analogs were significantly potentiated by thiorphan. Capsaicin (10 microM) produced a contraction which was unaffected by thiorphan. Both capsaicin and NKA-induced contractions were antagonized by Spantide at concentrations (5-10 microM) which had no effect against the atropine-sensitive contractions produced by electrical field stimulation. Capsaicin (1 microM) produced a consistent release of SP-like immunoreactivity (SP-LI) and a second application of the drug had no further effect, indicating complete desensitization. SP-LI release by capsaicin was almost doubled in the presence of thiorphan. These findings indicate that NK-2 and possibly some NK-3 receptors mediate the contractile response of the guinea-pig gallbladder to tachykinins. Both exogenous and endogenous (released by capsaicin) SP were degraded to a significant extent in this organ via a thiorphan-sensitive mechanism, the identity of which remains to be established.     

Inhibition of neurogenic vasodilation and plasma extravasation by substance P antagonists, somatostatin and [D-Met2, Pro5]enkephalinamide

The substance P (SP) analogues [D-Pro2, D-Phe7, D-Trp9]SP and [D-Pro2, D-Trp7,9]SP, which have been reported to be SP antagonists, inhibited the vasodilation and plasma extravasation induced by antidromic stimulation of the saphenous nerve or by i.a. infusion of SP. Somatostatin inhibited the vasodilatation and plasma extravasation induced by saphenous nerve stimulation, but had no effect on the vascular responses to i.a. infused SP. The opiate agonist [D-Met2, Pro5]enkephalinamide inhibited the vasodilation evoked by antidromic nerve stimulation in a naloxone reversible manner, but did not change the effect of i.a. infusion of SP. Calcitonin and caerulein had no effect on neurogenic vasodilatation. These results further support the concepts that neurogenic vasodilatation and plasma extravasation are mediated by SP, and that somatostatin and opiates inhibit the release of SP from peripheral sensory nerve endings.     

The effects of depolarizing agents and neuropeptides on dopamine release from striatal synaptosomes

Synaptosomes (isolated nerve endings) from rat corpus striatum responded to several depolarizing agents by releasing dopamine. Among these agents were KCl, glutamic acid, ouabain, and veratrine. Substance P hexapeptide (SP6) also caused dopamine release, but the magnitude of this effect was small and variable. A number of other neuropeptides (cholecystokinin 1–8, des-Tyr-γ-endorphin, Leu⁵-β-endorphin and substance P) did not alter dopamine release. SP6-induced dopamine release may result from substance P receptor-induced depolarization; however, the lack of robustness of the response in this preparation makes it unsuitable for studying agonists and antagonists of substance P.     

Substance-P antagonists: effect on spontaneous and drug-induced locomotor activity in the rat

The substance P (SP) antagonists (D-Pro4, D-Trp7,9, Leu11) SP(4-11), (D-Pro4, D-Trp7,9, Phe11)SP(4-11) and (D-Pro4, D-Trp7,9,10, Leu11) SP (4-11) were infused into the lateral ventricles (i.c.v.) and their effects on spontaneous and drug-induced locomotor activity were investigated. The drug DiMeC7, the stable substance P agonist, was used to stimulate locomotor activity because of its prolonged action. Only (D-Pro4, D-Trp7,9,10) SP (4-11) was found to attenuate the drug-induced increases in motor activity, indicating that it is a substance P antagonist with activity in the CNS.     

Structure-activity relationship of C-terminal hexa- and heptapeptide substance P antagonists as studied in the guinea-pig ileum

The 14 C-terminal heptapeptide analogues and one hexapeptide analogue of substance P (SP) were synthesized on the basis of the SP antagonist [D-Pro2,D-Trp7,9]SP-(1-11). They were tested in the guinea-pig ileum preparation for spasmogenic and antagonistic activities. All analogues except two had antagonistic activity. Spasmogenic activity was observed in three heptapeptide SP antagonists: [Arg5,D-Trp7,D-pCl-Phe9]SP-(5-11), [Arg5,D-Trp7,9,p-Cl-Phe8]SP-(5-11) and [Arg5,D-Trp7,9,Nle11]SP-(5-11). However, this effect became greatly reduced upon successive applications in almost all ileum preparations. For antagonistic potency D-Trp turned out to be of greater importance in position 9 than in position 7 of the SP molecule. The presence of a free amino group at the N-terminal of the peptide was also of significant importance for antagonistic potency. Exchange of Met11 for Nle resulted in a considerable increase of antagonistic potency, while other substitutions in this position were ineffective or slightly reduced the antagonistic effect in the ileum preparation.     

Antagonist discrimination between subtypes of tachykinin receptors in the guinea-pig ileum

The effects of substance P and eledoisin on spontaneous and electrically-evoked release of [3H]acetylcholine, and on smooth muscle were studied in the guinea-pig myenteric plexus-longitudinal muscle preparation preloaded with [3H]choline. Substance P and eledoisin caused transient increases in spontaneous release of [3H]-acetylcholine and in longitudinal muscle tone. Both tachykinins were equipotent in contracting the muscle, but eledoisin was more potent than substance P in eliciting [3H]acetylcholine release. The release caused by substance P was enhanced in the presence of naloxone and scopolamine which suggests that the release is modulated through opioid and muscarinic receptors. Substance P and eledoisin inhibited the release of [3H]acetylcholine evoked by electrical stimulation at 0.1 Hz. The inhibition was not due to an activation of alpha-adrenoceptors, histamine or opioid receptors. The substance P antagonists (D-Pro2, D-Trp7,9)SP (10 and 30 microM) and (Arg5, D-Trp7,9, Nle11)SP5-11 (1 and 10 microM) competitively antagonized both the contractile effects of substance P and eledoisin, and the inhibition by the tachykinins of the electrically-evoked release of [3H]acetylcholine. The increase in spontaneous [3H]acetylcholine release elicited by substance P and eledoisin was not prevented by the substance P antagonists. The results suggest that the neuronal receptor whose activation causes inhibition of acetylcholine release and the smooth muscle receptor correspond to the SP-P type, whereas the neuronal receptor mediating an increase in spontaneous acetylcholine release is of the SP-E type. The two antagonists, (D-Pro2, D-Trp7,9)SP and (Arg5, D-Trp7,9, Nle11)SP5-11, selectively block only the SP-P receptor.     

Substance P analogues containing D-histidine antagonize the behavioural effects of intrathecally co-administered substance P in mice

The antagonistic effect of newly synthesized substance P (SP) analogues containing D-histidine was examined on behavioural responses induced in mice by SP, neurokinin (NK) A, physalaemin, eledoisin, somatostatin and bombesin. [D-Pro2,D-Trp7,9]SP (DPDT-SP) and [D-Arg1,D-Trp7,9,Leu11]SP (spantide) were used as references for comparison. When co-administered with SP intrathecally, all the SP analogues used decreased the SP-induced response which consists of scratching, biting and licking. DPDT-SP and spantide attenuated non-specifically the SP-like behavioural responses induced by physalaemin, eledoisin, NK A and somatostatin. In general, the introduction of D-histidine in position 9 of the SP molecule resulted in potent antagonistic activity of the SP derivative on the behavioural responses to SP. Of these SP analogues, [D-Arg1,D-Pro2,4,D-Phe7,D-His9]SP attenuated selectively the behavioural responses produced by NK-1 receptor agonists such as SP and physalaemin. Simultaneous injection of [D-Phe7,D-His9]SP-(6-11) selectively inhibited the SP-induced behavioural response without affecting the other peptide-induced behavioral response. The results suggest that the behavioural antagonism induced by [D-Arg1,D-Pro2,4,D-Phe7,D-His9]SP and [D-Phe7,D-His9]SP-(6-11) is probably due to the specific blockade of spinal NK-1 receptors.     

Substance P and its fragments affect Ca2+/calmodulin-dependent synaptosomal membrane protein phosphorylation from rat cerebral cortex.

1. We have used synaptosomal membranes to study the influence of substance P and its fragments and analogues of its C-terminal fragment on Ca2+/calmodulin-dependent synapsin I endogenous phosphorylation. 2. SP1-11, SP1-4, [Tyr8]SP6-11 and [pGlu6, Tyr8]SP6-11 at 10(-3) M greatly inhibited synapsin I phosphorylation. 3. SP6-11 at all investigated concentrations and SP1-11, SP1-4, [Tyr8]SP6-11, [pGlu6, Tyr8]SP6-11 at 10(-4) and 10(-5) M were ineffective. 4. The results indicate that SP1-11 and its N-terminal fragment and analogues of its C-terminal fragment act on the phosphorylation of specific synaptic protein (synapsin I) and therefore may influence the release of neurotransmitters, membrane conductance and potentiation or inhibition of other signalling systems.     

Regulation of the substance P-induced contraction via the release of acetylcholine and gamma-aminobutyric acid in the guinea-pig urinary bladder.

1. The action of substance P (SP) on the release of gamma-aminobutyric acid (GABA) and acetylcholine (ACh) and on contraction were studied in strips of the guinea-pig urinary bladder. Substance P induced a dose-dependent contraction of strips of guinea-pig urinary bladder (EC50 = 1.2 x 10(-9) M). This contraction was not altered by tetrodotoxin, but with a dose of 10(-9) M and less, there was a complete inhibition by 10(-6) M) atropine. Contractions initiated by 3 x 10(-9) M) SP or more were partly inhibited by atropine. The EC50 value of substance P in the presence of atropine was 7.0 x 10(-9) M. 2. Substance P induced a Ca2+-dependent and tetrodotoxin-resistant release of [3H]-acetylcholine (ACh) from strips of urinary bladder preloaded with [3H]-choline (EC50 = 4.9 x 10(-10) M), and this release was antagonized by [D-Pro2,D-Trp7,9] substance P. 3. Bicuculline increased the substance P-induced contraction and the release of [3H]-ACh from the strips. 4. Substance P induced a Ca2+-dependent and tetrodotoxin-sensitive release of [3H]-gamma-aminobutyric acid (GABA) from strips preloaded with [3H]-GABA (EC50 = 2.6 x 10(-9) M), and this release was antagonized by [D-Pro2,D-Trp7,9] substance P. 5. Therefore, substance P appears to exert excitatory effects on the contractility of urinary bladder predominantly by stimulating its own receptor located on the cholinergic nerve terminals. GABA released by substance P inhibits stimulation of the cholinergic neurone. However, the direct action of substance P on the cholinergic neurone is more potent that the indirect action via GABA release.     

Stimulatory effect of substance P on the spontaneous release of newly synthesized [3H]dopamine from rat striatal slices: a tetrodotoxin-sensitive process

Striatal slices from the rat were continuously superfused with [3H]tyrosine in order to estimate the release of newly synthesized [3H]dopamine [( 3H]DA). Substance P (SP) and neuromedin K (NKB) stimulated the spontaneous release of [3H]DA when used in concentrations (from 10(-9) M to 10(-7) M). The stimulatory effect of substance P (10(-8) M) was prevented completely when slices were superfused with tetrodotoxin (10(-7) M) or the substance P antagonist (D-Arg1,D-Pro2,D-Trp7,9,Leu11) substance P (10(-5 M) indicating that the response evoked by substance P was mediated by substance P receptors but that these were not located on DA nerve terminals. In addition, substance P did not modify the stimulatory effect of acetylcholine (ACh) (10(-5) M) on the spontaneous release of [3H]DA since the effects of substance P (10(-7) M) and ACh (10(-5) M) were additive.     

Dehydro keto methylene and keto methylene analogues of substance P. Synthesis and biological activity

The synthesis of dehydro keto methylene and keto methylene analogues of substance P using classical peptide synthesis is described. The following analogues were prepared: [pGlu6,Gly9psi(COCH2)(RS)Leu10]SP6-11 (4) and [pGlu6,-(RS)Phe7 psi(COCH2)(RS)Phe8]SP6-11 (8). The use of an improved deprotection scheme employing Meerwein's reagent (Et3OBF4) made possible the syntheses of the novel dehydro keto methylene analogue [pGlu6,(RS)Phe7 psi-(COCH2)delta(E)Phe8]SP6-11 (26) adn the tetrapeptide analogue [pGlu6,(RS)Phe8 psi(COCH2)Gly9]SP6-9(-OMe) (23). Compound 4 was a weak agonist in provoking contractions of the guinea pig ileum. Compound 26 was a potent inhibitor of SP degradation in rat hypothalamus preparations, with an IC50 value of 1.8 microM.     

Substance P: structural requirements for the activation of brain catecholamine synthesis and locomotor activity in rats

Intracerebroventricularly administered Arg-Pro-Lys-Pro-Gln-Gln-Phe-Gly-Leu-Met-NH2 (substance P, SP) enhanced the accumulation of DOPA after inhibition of the aromatic L-amino acid decarboxylase in the rat brain. SP also stimulated locomotor activity in a dose-dependent manner. A total of 31 structural analogues of SP were evaluated with respect to the action on brain monoamine synthesis as well as on locomotor activity. Catecholamine synthesis: SP1-10 was inactive which indicated that the [Met11]-NH2 terminal is essential for biological activity; [Leu10], [Phe7] and [Gln6] were also essential for activity; the minimum length requirement for activity was a hexapeptide amide structure. D-Amino acids in positions 8 or 9 increased activity. [D-Pro2]p-SP and [pGlu5, Gly7]-SP5-11 were active in the dopamine-rich areas, but inactive in the noradrenaline (norepinephrine)-predominant parts of the brain. The inactive [Ile7]-SP potentiated the effect of SP. Neither SP nor its analogues, with the exception of [Lys5,D-Leu8,D-Phe9]-SP5-11, increased the synthesis of 5-hydroxytryptophan (5-HTP). Locomotor activity: SP1-10 and [D-Phe9]-SP were as active as SP; [Ile7]-SP and [Ile7, Ile8]-SP were inactive and they did not antagonize the effect of SP. The results indicate that after chemical manipulation of the SP molecule it is possible to obtain great variation in activity and to dissociate to some extent the behavioural effects from those on brain catecholamine synthesis.     

In vitro activity and selectivity of glucosidic SP(6-11) analogues

The relative potencies of a series of substance P (6-11) analogues have been determined for spasmogenic activity in the guinea pig ileum in vitro and for potentiation of electrically evoked contractions in the rat vas deferens in vitro. ED50 values were determined for the new analogues. Substance P and its methyl ester were used as standard agonists. Substitution of Gly9 by Pro on [Glu6]SP(6-11) increased four times the activity on the NK-1 receptor. The glycosilation of [Glu6]SP(6-11) by the incorporation of a beta-D-glucopyranosyl amide residue on the gamma-carboxyl group of Glu6 reduced both the activity and selectivity. The simultaneous substitution of Gly9 by Pro and the incorporation of a monosaccharide moiety on the gamma-carboxyl of Glu6 on [Glu6]SP(6-11) yielded an analogue with 60-fold enhanced selectivity relative to substance P for the NK-1 receptor. These results may indicate that the critical factor providing potency to SP(6-11) analogues is mostly related to conformational rather than hydrophilicity aspects of the molecular structure.     

Effects of tachykinins on uterine smooth muscle

1. Sensory nerves supplying the mammalian uterus have been shown to contain substance P (SP) and neurokinin (NK)A. This review presents some of the advances that have led to a greater understanding of the effects of tachykinins on uterine smooth muscle. 2. The cell-surface peptidase neprilysin (EC.3 24.11, endopeptidase 24.11, enkephalinase, CALLA, CD10) has been shown to play a major role in regulating the actions of tachykinins on both rat and human myometrium. Because this peptidase is known to be regulated by steroids and pregnancy, its effects may be of physiological relevance. 3. Tachykinins produce contractions of isolated myometrial preparations from non-pregnant rats and mice. The NK2 receptor mediates these effects in rat uterus, while the NK1 receptor may mediate these effects in the mouse uterus. 4. The effects of tachykinins have been examined on myometrial preparations obtained at Caesarean section from near-term pregnant women. In the presence of the peptidase inhibitors (thiorphan, captopril and bestatin), the mammalian tachykinins SP, NKA and NKB produced concentration-dependent uterine contractions. 5. The order of agonist potency NKA > SP = NKB suggested that NK2 receptors mediate uterine contractions in the human. This was confirmed using the stable analogues [Sar9,Met(O2)11]SP, [Lys5MeLeu9Nle10]NKA(4-10) and [N-MePhe7]NKB, which are NK1, NK2 and NK3 receptor selective, respectively. Only [Lys5MeLeu9Nle10]NKA(4-10) produced concentration-related contractions of human uterine smooth muscle. 6. The experimental findings described in the present review, taken together with results published previously in the literature, indicate that tachykinin peptides may play a physiological or pathophysiological role in regulating uterine smooth muscle activity. However, more extensive research will be required to confirm such a role for these peptides.     

Behavioural and antinociceptive effects of intrathecally injected substance P analogues in mice

The antinociceptive effects and antagonism of substance P (SP)-induced behaviour were examined after intrathecal injections in mice. When coadministered with SP, the SP analogues attenuated the SP-induced behaviour to various extents with [D-Arg1,D-Pro2,4,D-PHe7,D-His9]SP as the most potent antagonist. Physalaemin and eledoisin brought about a SP-like behavioural response. [D-Arg1,D-Trp7,9,Leu11]SP inhibited the response to eledoisin but not that to physalaemin. The SP analogues substituted with D-Trp7,9 and with Leu or Val in position 11 produced the strongest antinociceptive effects. Pretreatment with naloxone (5 mg/kg, i.p.) abolished the antinociceptive effects of [D-Trp7,9,Leu11]SP, implying that opiate receptors in the spinal cord mediate at least in part the antinociceptive effects. Animals under pentobarbital anesthesia showed a potentiated antinociceptive effect in the tail-flick test. In conclusion, we found that the SP analogues tested exerted varying degrees of antinociception, and that this was probably at least in part mediated by activation of spinal opiate receptors, whereas the behavioural antagonism was probably due to the blockade of spinal SP receptors.     

A comparison of the effects of three substance P antagonists on tachykinin-stimulated [3H]-acetylcholine release in the guinea-pig ileum

The potencies of three tachykinin antagonists [D-Pro4,D-Trp7,9,10]SP(4-11), [D-Arg1,D-Pro2,D-Trp7,9,Leu11]SP(1-11) and [D-Arg1,D-Trp7,9,Leu11]SP(1-11) (spantide) against eledoisin were examined in the guinea-pig ileum myenteric plexus, where a continuous superfusion system was employed to examine evoked release of [3H]-acetylcholine [( 3H]-ACh]); effects on mechanical activity of the preparations were also measured. Eledoisin was chosen as the standard tachykinin agonist since the rank order of potency observed in evoking release was eledoisin, kassinin, substance P, physalaemin; on this basis is may be presumed that an 'SP-E' type receptor was involved in the release process. The two undecapeptide antagonists both significantly reduced the response to eledoisin (10 nM) as assessed by both [3H]-ACh release and mechanical activity which under these conditions was largely dependent on ACh release, and the response levels could be restored by increasing the concentration of eledoisin to 100 nM. The pA2 values for the two antagonists were estimated as 5.3 for [D-Arg1,D-Pro2,D-Trp7,9,Leu11]SP(1-11) and 5.2 for [D-Arg1,D-Trp7,9,Leu11]SP(1-11). [D-Pro4,D-Trp7,9,10]SP(4-11) was markedly less potent with a pA2 value of less than 4.8. All three antagonists possessed considerable inherent stimulatory activity as measured both by [3H]-ACh release and mechanical activity, [D-Pro4,D-Trp7,9,10]SP(4-11) being the most active in this respect, a 10 microM concentration producing 50% of the response seen with 10 nM eledoisin. These findings are discussed both in relation to tachykinin receptor classifications and limitations in the use of such antagonists in the study of the role of tachykinins in neurotransmission.