Differential release of histamine and eicosanoids from human skin mast cells activated by IgE-dependent and non-immunological stimuli.

1. Cells were dispersed from human foreskin using a mixture of collagenase and hyaluronidase and separated into mast cell-depleted (less than 1%) or enriched (greater than 75%) preparations by density-gradient centrifugation. 2. Challenge of gradient fractions with epsilon-chain-specific anti-human IgE stimulated the release of histamine, prostaglandin D2 (PGD2) and leukotriene C4 (LTC4). The release of eicosanoids was significantly correlated with that of histamine, suggesting that they are derived from the mast cell population of the dispersate. In highly purified (76.2 +/- 4.2%) mast cell preparations, maximum net release of histamine, PGD2 and LTC4 was 3432 +/- 725, 84.9 +/- 10.8 and 6.6 +/- 1.2 pmol/10(6) nucleated cells. 3. The non-immunological stimuli substance P, vasoactive intestinal peptide (VIP), somatostatin, compound 48/80, morphine and poly-L-lysine released similar amounts of histamine to anti-IgE, but 12 to 21 fold less PGD2 and LTC4. 4. These studies suggest that IgE-dependent and non-immunological stimuli activate human skin mast cells by different secretory mechanisms, a hypothesis supported by our previous findings of differences in Ca2+ requirements and time-course of histamine release. Activation by the non-immunological mechanism may be of importance in vivo due to the close anatomical association between skin mast cells and dermal nerve-terminals containing neuropeptides.     

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.     

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.     

NK-1 receptor mediation of neurogenic plasma extravasation in rat skin.

1. Plasma extravasation was induced by electrical nerve stimulation and by perfusion of tachykinins over a vacuum-induced blister base on rat footpad. 2. Stimulation of the sciatic nerve (18 V, 15 Hz, 0.5 ms) for 20 min produced a significant increase in the protein content of the perfusate. The response in capsaicin pretreated rats was only 4% of the control response. This indicates that the electrically-induced plasma extravasation response was mediated by capsaicin-sensitive sensory fibres. 3. Exogenous perfusion of the mammalian tachykinins substance P, neurokinin A and neurokinin B and the non-mammalian tachykinins physalaemin, kassinin and eledoisin was used to determine the tachykinin receptor type mediating the plasma extravasation response. Dose-response curves of the tachykinins (10(-9) M-10(-4) M) gave a rank order of potency of substance P = physalaemin greater than eledoisin greater than or equal to kassinin greater than neurokinin B = neurokinin A. 4. In addition, specific agonists of neurokinin receptors were perfused. Perfusion of [Glp6, D-Pro9] SP6-11 and [Glp6, L-Pro9]SP6-11 demonstrated that the L-Pro isomer was much more potent than the D-Pro isomer. 5. The rank order of potency and the greater potency of [Glp6, L-Pro9]SP6-11 over its D-isomer indicate an NK-1 neurokinin receptor mediates plasma extravasation in rat footpad skin.     

Release of histamine by substance P

1. The basic peptide substance P causes histamine release from peritoneal mast cells of the rat in vitro whereas the closely related neutral peptides eledoisin and physalaemin do not. 2. Infusion of substance P (7.4 nmol min-1), but not of eledoisin (8.4 nmol min-1) or physalaemin (7.9 nmol min-1), into the rat hindquarter preparation caused a more than 4-fold increase of the histamine content in the venous outflow. The outflow of 5-HT remained unchanged under infusion of all three peptides. 3. No histamine depletion in the skin of the rat hind paw was observed following antidromic stimulation of the saphenous nerve or cutaneous application of mustard oil. Infusion of substance P (7.4 nmol min-1) caused a 47% depletion of histamine in the paw skin although only a small proportion of the infused substance P seemed to enter the tissue from the blood vessels. 4. The results further substantiate the view that substance P upon release from peripheral nerve endings induces release of histamine from cutaneous mast cells, a mechanism which contributes to neurogenic vasodilatation and plasma extravasation.     

On the actions of substance P,somatostatin, and vasoactive intestinal polypeptide on rat peritoneal mast cells and in human skin

Substance P (SP), somatostatin (Som), and vasoactive intestinal polypeptide (VIP) induced a concentration-dependent release of histamine from isolated rat peritoneal mast cells. The release of histamine induced by these neuropeptides was inhibited by preincubation of the cells with the SP analogue [D-Pro4,D-Trp7,9,10]-SP4-11 (SP-A) (10 microM), and also by benzalkonium chloride (10 microM). In addition, SP-A inhibited histamine release induced by compound 48/80, whilst that induced by goat anti-(rat-IgE) was unaffected. In human skin, intradermal injection of SP, Som, or VIP produced flare and wheal responses. The flares to all three peptides were inhibited by preinjection of the skin with SP-A (25 pmol), whilst the wheal responses were unaffected. It is concluded that the receptors mediating histamine release and the flare response are similar, and that SP, Som, and VIP are acting at a similar receptor to produce these effects. It is probable that this receptor is also the site of action of compound 48/80.     

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.     

Neurokinin A-stimulated phosphoinositide breakdown in rabbit iris sphincter muscle.

Specific [3H]-substance P binding was saturable and of high affinity (KD = 2.5 nM) with a Bmax of 725 fmol/mg protein in the isolated rabbit iris sphincter muscle. The competition for [3H]-substance P binding was in the order of eledoisin greater than substance P greater than kassinin greater than neurokinin B greater than neurokinin A greater than physalaemin. In the same preparation, neurokinin A, as well as substance P induced a concentration-related accumulation of [3H]-inositol phosphates (IPs), and the maximum increase was about 200% of the control at 10(-4) M. [D-Arg1, D-Trp7,9, Leu11]-substance P (SP) and [D-Pro2, D-Trp7,9]-SP (10(-3) M) inhibited substance P or neurokinin A (10(-4) M)-induced phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis significantly. [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP (10(-3) M) also inhibited neurokinin A (10(-4) M)-induced PIP2 hydrolysis significantly. Neurokinin A and substance P produced concentration-related contractions in normal Ca(2+)-containing medium. The contractile response was weaker in Ca(2+)-free medium, and there was no response in 0.2 mM EGTA medium. In Ca(2+)-free medium, the basal level of [3H]-IPs accumulation was smaller than that in normal medium, and neurokinin A and substance P significantly increased PIP2 hydrolysis. In the 0.2 mM EGTA containing medium, neurokinin A and substance P did not stimulate the PIP2 hydrolysis.(ABSTRACT TRUNCATED AT 250 WORDS)     

The hamster isolated trachea: a new preparation for studying NK-2 receptors

Mammalian tachykinins (substance P, neurokinin A and neurokinin B) produced a concentration-related contraction of the hamster isolated trachea with the following order of potency: NKA congruent to NKB much greater than substance P (SP). NKA and NKB were 280 and 203 times more potent than SP, respectively. The action of NKA, NKB or SP was not significantly modified in presence of thiorphan (10 microM), atropine (1 microM), mepyramine (1 microM) or indomethacin (5 microM). [Nle10]NKA-(4-10) or [beta Ala8]NKA-(4-10), two selective NK-2 receptor agonists, displayed good activity while other synthetic agonists, selective for NK-1 or NK-3 receptors, had little or no effect. The contractile response to tachykinins did not undergo appreciable desensitization and was promptly reversed by washing out. These data indicate that NK-2 receptors are the main if not the sole mediators of the response of the hamster isolated trachea to tachykinins, whose action is independent from cholinergic nerves, histamine release or prostaglandin production. Further, no significant peptide degradation by a thiorphan-sensitive mechanism occurs in this organ.     

The substance P receptor on rat mast cells and in human skin

(D-Pro4 D- Trp7 ,9,10)SP4-11 (SPA) has been shown to be a competitive antagonist of the histamine releasing action of substance P in rat peritoneal mast cells. Antagonist activity of SPA is expressed in the concentration range 1 to 10 microM, but at higher concentrations SPA releases histamine. SPA inhibits the flare response induced by substance P in human skin but is without effect on the wheal response. Up to 12.5 pmol SPA produces neither wheal nor flare response by itself. The structurally related peptide, kassinin , does not cause histamine release from rat mast cells at concentrations up to 10 microM whereas the methyl ester of substance P was found to 1.6 times more active than substance P in this respect. The findings are discussed in terms of the classification of substance P receptors and the mechanism of wheal and flare in human skin.     

Effects of neurokinins on the isolated pig coronary artery

The actions of substance P (SP), neurokinin A (NKA), neurokinin B (NKB), physalaemin (PHY), kassinin (KAS) and eledoisin (ELE) were investigated on transversally cut strips of pig coronary artery. All tachykinins produced vasodilatation of coronary arteries precontracted with ACh; 10(-5) M. The order of potency was: SP = PHY ELE greater than KAS greater than NKA greater than NKB, with the ED50 values being 0.38, 0.38, 1.2, 2.6, 8.3 and 34.0 nM, respectively. Continued superfusion of SP (7.4 X 10(-9) M) desensitized the coronary arteries which were refractory to the vasodilator action of NKA, NKB, PHY and KAS. The arteries nevertheless dilated upon the addition of noradrenaline (NA) and bradykinin (BK). Endothelium-removed preparations did not respond to any of the tachykinins. However, tissues devoid of endothelium relaxed in response to both NA and vasoactive intestinal polypeptide (VIP). Three octapeptide antagonists, [D-Pro4,Ala6,D-Trp7,9,Nle11]SP-(4-11) (compound I), [D-Pro4,Ser6,D-Trp7,9,Nle11]SP-(4-11) (compound II) and [D-Pro4,D-Trp7,9,10,Phe11]SP-(4-11) (compound III) were examined as potential antagonists of tachykinin-induced vasodilatation. Compounds I and II blocked the actions of SP and NKA but not that of PHY. Compound III effectively blocked the actions of SP and PHY. We conclude that the pig coronary artery possesses a 'NK-P/SP-P' type receptor, and that this receptor is probably localized on the endothelium.     

Nanomolar concentrations of neuropeptides induce histamine release from peritoneal mast cells of a substrain of Wistar rats.

Substance P causes histamine release from rat peritoneal mast cells probably through direct activation of a specific G protein at micromolar concentrations. We found that peritoneal mast cells of a substrain of Wistar rats (Std:Wistar) responds to nanomolar concentrations of substance P by releasing histamine in a concentration-dependent manner. In addition, potent histamine release from peritoneal mast cells of the substrain rats was also induced by neurokinin A in a concentration-dependent fashion. Histamine release induced by low concentrations of substance P was significantly blocked by a tachykinin NK1 receptor antagonist, CP-96345 [(2S,3S)-cis-2-(diphenylmethyl)-N-[(2-methoxyphenyl)-methyl]-1-aza bicyclo[2.2.2]octan-3-amine dihydrochloride], whereas that induced by concentrations as high as 10 microM appeared resistant to the antagonist. The concentration-histamine release curve for neurokinin A was parallel-shifted to the right by the drug. A tachykinin NK2 receptor antagonist, SR-48968 [(S)-N-methyl-N[4-(4-acetylamino-4-phenyl piperadino)-2-(3,4-dichlorophenyl)butyl]benzamide], did not influence release stimulated by substance P and neurokinin A. On the other hand, peritoneal mast cells of Sprague-Dawley and other Wistar rats did not respond to neurokinin A. At over 1 microM but not at nanomolar concentrations, substance P caused modest histamine release from peritoneal mast cells of these rats. The results suggest that neurokinin A and nanomolar, but not micromolar concentrations of substance P stimulate tachykinin NK receptors on the peritoneal mast cells of Std:Wistar rat to release histamine.     

Biological evaluation of substance P antagonists.

Five undeca- and six C-terminal heptapeptide substance P (SP) analogues were tested for their capacity to block the contractile effect of SP on the guinea-pig isolated taenia coli. They had one feature in common, namely substitutions in positions 7 and 9 in the SP molecule. In the majority of analogues D-tryptophan was used for these substitutions. All analogues tested were found to be competitive antagonists to exogenous SP and to be capable of blocking the electrically induced non-cholinergic, non-adrenergic neuronal contraction of the taenia. Of the undecapeptides, (D-Arg1, D-Pro2, D-Trp7,9, Leu11) SP and (D-Arg1, D-Trp7,9, Leu11) SP (Spantide) had the highest pA2 value, 7.1-7.2, and the lowest IC50 value, 10(-6) M. The pA2 values of the heptapeptides were generally lower. Three of the most potent antagonists were tested for specificity and found to block the smooth muscle contraction induced by SP, physalaemin, eledoisin and bombesin but not that induced by bradykinin, carbachol, 5-hydroxytryptamine, histamine, prostaglandins and vasopressin. The SP antagonists were also tested for spasmogenic effect on the taenia and for their capacity to release histamine from rat isolated peritoneal mast cells. The spasmogenic activity displayed by most of the SP antagonists tested is likely to be related to their ability to release histamine since the contractile response was reduced by mepyramine, a histamine H1-receptor antagonist. (D-Arg1, D-Trp7,9, Leu11) SP was notable for combining a high antagonistic potency with a weak spasmogenic effect (and poor histamine releasing effect).     

Evidence for multiple tachykinin receptor subtypes on the rabbit iris sphincter muscle

The actions of mammalian tachykinins (substance P, substance K/neurokinin a, neuromedin K/neurokinin b) and non-mammalian tachykinins (eledoisin, kassinin, physalaemin) were compared on the rabbit pupillary sphincter. All acted as direct spasmogens with potencies in the order: eledoisin greater than physalaemin = neurokinin b = substance P greater than kassinin greater than neurokinin a. However, their actions could be divided into at least two categories on the basis of similar kinetics of contractions, differential sensitivity to the tachykinin antagonist (D-Arg1, D-Pro2, D-Trp7,9, Leu11) substance P and specific cross-protection against phenoxybenzamine inactivation by structurally related tachykinins. The relationship between these observations and the suggested "P" and "E" subtypes of tachykinin receptors is discussed.     

Contractile effects of substance P and other tachykinins on the mouse isolated distal colon.

1. Substance P (SP), physalaemin, eledoisin and kassinin induced concentration-related contractions of the longitudinal muscle of the mouse distal colon. The responses were not antagonized by atropine (1.5 x 10(-7) M), mepyramine (2.5 x 10(-7) M), methysergide (5 x 10(-7) M), timolol (10(-6) M), phentolamine (10(-6) M) or naloxone (4 x 10(-7) M). They were enhanced by tetrodotoxin (TTX, 1.5 x 10(-7) M). These observations indicate that the contractile responses to the tachykinins result from a direct activation of smooth muscle cells. 2. The contractile activity provoked by SP and physalaemin was inhibited by nifedipine (a Ca2+-entry blocker) and was abolished in Ca2+-free EGTA solution. Such data suggest that the myogenic effects of SP and physalaemin are mainly dependent on their ability to promote Ca2+ influx. 3. Eledoisin and kassinin evoked a contractile response in the absence of external Ca2+ and their myogenic activity was, to some extent, resistant to the inhibitory effect of nifedipine. This may indicate that an additional process, probably the release of an intracellularly bound Ca2+ store, participates in the mechanism by which eledoisin and kassinin contract the mouse distal colon. 4. After desensitization of the mouse distal colon to SP, the contractile activity provoked by SP or physalaemin was totally abolished whilst the responses evoked by eledoisin and kassinin were barely affected. These observations and other experimental findings indirectly support the assumption that the mouse distal colon could possess different tachykinin-binding sites.     

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.     

Classification of tachykinin receptors in muscularis mucosae of opossum oesophagus.

1. Muscularis mucosae of the distal oesophagus of the opossum contracts in response to substance P and to a variety of tachykinins. To delineate the nature of the receptors present in this tissue, we evaluated contractile responses to substance P, neurokinin A, neurokinin B, eledoisin and analogues believed to be highly selective for NK-1, NK-2 and NK-3 receptors. In addition, the effects of prolonged exposure to each of these agents (10(-6) M or 10(-5) M) on contractile responses to substance P and to itself were evaluated. Similarly effects of prolonged exposure to the various tachykinins and their analogues on the field-stimulated responses of this muscle were studied. 2. All naturally occurring tachykinins were full agonists and differed in potency (comparing ED50 values) by less than ten fold. In nearly all cases there was cross tachyphylaxis between substance P and the other tachykinins and each reduced tonic responses to field stimulation, a response previously shown to be mediated by a substance P like agent. Eledoisin failed to cause tachyphylaxis under the conditions of these experiments. 3. When highly selective tachykinin analogues were used, only that believed to activate NK-1 receptors was a full agonist. [beta-Ala4,Sar9,MetO2(11)]SP(4-11) was also only slightly less potent than substance P. In contrast, an agonist selective for NK-2 (NK-A) receptors, [Nle10]NKA(4-10), and one selective for NK-3 (NK-B) receptors, [beta-Asp4, MePhe7]NKB(4-10) were unable to produce a response equal to 50% of the maximum even at 10(-5) M. However, all three selective tachykinin analogues reduced responses to substance P but not to carbachol.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of the responses to the sensory neuropeptides, substance P, neurokinin A, neurokinin B and calcitonin gene-related peptide and to trigeminal nerve stimulation in the iris sphincter muscle of the rabbit

Three mammalian tachykinins (substance P, neurokinin A and B) and two non-mammalian ones (eledoisin and physalaemin) produced potent contractions of the isolated rabbit iris sphincter muscle. The rank order of potencies was eledoisin greater than neurokinin B = physalaemin greater than substance P greater than neurokinin A. The maximum efficacy was much the same. The contractile responses to neurokinin A and eledoisin developed more rapidly than did those to the other tachykinins used and were selectively attenuated by [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP. Electrical transmural stimulation produced a contraction consisting of cholinergic and tachykininergic components. The tachykininergic component was abolished by pretreatment with capsaicin or by trigeminal denervation (Fujiwara et al., 1984). [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP attenuated the tachykininergic component, but not the cholinergic one. KCl and capsaicin also produced a tachykininergic contraction which was inhibited by [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP. Calcitonin gene-related peptide affected neither the iris sphincter muscle nor the response to electrical transmural stimulation. These results suggest that the tachykininergic responses induced by electrical transmural stimulation, KCl and capsaicin are predominantly mediated by neurokinin A, probably released from the peripheral endings of trigeminal nerves.     

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.     

Peptides and histamine release from rat peritoneal mast cells

Various vasoactive peptides were compared for their histamine releasing effects on rat mast cells. Neurotensin, substance P (SP), and kallidin were the most active natural peptides, followed by bradykinin; neurokinin A and B, bombesin, angiotensin and tuftsin were practically inactive. Several kinins and tachykinin-related peptides were tested in an attempt to characterize the receptors mediating histamine liberation. The order of potency of the kinins was the following: kallidin greater than [Tyr(Me)8]bradykinin = bradykinin greater than [desArg10]kallidin greater than desArg9-bradykinin, the same as that found in smooth muscle possessing receptors of the B2 type. Tachykinin-related peptides were potent stimulants and followed the order: [D-Tryp7,9,10]SP-(1-11) greater than [D-Pro2,D-Tryp7,9,10]SP-(1-11) greater than SP-(1-11) greater than SP-(1-9) greater than [D-Pro4,D-Tryp7,9,Leu11]SP-(4-11) greater than SP-(1-7) greater than SP-(4-11) greater than neurokinin A = neurokinin B, indicating that: (a) undecapeptide antagonists of SP behave as superagonists; (b) both N- and C-terminal portions of SP-(1-11) are essential for activity; and (c) receptors for the tachykinins mediating histamine release appear to be of the SP-P type.