Eledoisin-related Peptide Research Articles

Action of serine carboxypeptidase from Aspergillus saitoi on carboxyterminal amidated peptides.

The specificity of the serine carboxypeptidase from Aspergillus saitoi (EC 3.4.16.1) was investigated on carboxyterminal amidated peptides such as benzyloxycarbonyl(Z)-Ala-Phe-NH2, gastrin-related peptide, molluscan cardioexcitatory neuropeptide, eledoisin-related peptide, and (D-Ala2, Met5)-enkephalinamide. The enzyme did not hydrolyze Z-Ala-Phe-NH2. It acted only as a carboxyamidase for the carboxyterminal peptide bond of gastrin-related peptide and as an amidase for enkephalinamide. The enzyme had both carboxyamidase activity and amidase activity for molluscan cardioexcitatory neuropeptide and eledoisin-related peptide. Whether the enzyme acts as an amidase or carboxyamidase, the hydrophobicity of P3 and P4 positions of the substrate may be important. After removal of the carboxyterminal amino acid amide and/or ammonia, the enzyme catalyzed the sequential liberation of the amino acid from the carboxyterminus of the substrate.

Differing actions of convulsant and nonconvulsant barbiturates: An electrophysiological study in the isolated spinal cord of the rat

The effects of various pairs of convulsant and nonconvulsant barbiturates on mono-and polysynaptic activity were studied in the isolated spinal cord of the immature rat, using extracellular recording. The convulsant barbiturates, 5-ethyl-5-(3-methylbut-2'-enyl) barbituric acid (3M2B), 5-ethyl-5-(1,3-dimethylbut-1'-enyl) barbituric acid (1,3M1B) and (+)-5-(1,3-dimethylbutyl)-5-ethyl barbituric acid [(+) DMBB] all increased the monosynaptic reflex at concentrations between 5 and 50 μM with no change in polysynaptic activity. When the concentration was raised to between 100 and 300 μM, however, the convulsants all reduced the monosynaptic reflex, thus producing a biphasic dose-response relationship. The nonconvulsant barbiturates phenobarbital, 5-ethyl-5-(3-methylbut-1'-enyl) barbituric acid (3M1B), amylobarbital (3MB) and (−)-5-(1,3-dimethylbutyl)-5-ethyl barbituric acid [(−)DMBB] produced only a decrease in mono- and polysynaptic reflexes. At concentrations which enhanced the monosynaptic reflex, the responses of motoneurones to glycine and eledoisin-related peptide (an analogue of substance P) were reduced by (+)DMBB, while 1,3M1B and 3M2B had no significant effects upon any of the neurotransmitters tested. At concentrations which depressed the monosynaptic reflex, the convulsants all reduced the response to glycine whereas the nonconvulsant barbiturates all increased the response to GABA. With the exception of phenobarbital, both convulsant and nonconvulsant barbiturates produced a direct depolarisation of the presynaptic terminal membrane, with only the convulsants producing a depolarisation of the membrane of the motoneurone. Using another convulsant barbiturate, 5-(2-cyclohexylideneethyl)-5-ethyl barbituric acid (CHEB), this direct depolarising action was found to be calcium-dependent.

Analgesic and cardiovascular effects of centrally administered substance P

Substance P (SP) injected intracerebroventricularly (ICV) into rabbits caused dose-related thermal analgesia with the maximum effect after 2 μg. The analgesia was measured by timing the withdrawal of the rabbit's ear from an infrared beam. Equimolar amounts of the related peptides physalaemin and eledoisin-related peptide also caused analgesia, but the SP N-terminal fragment (1–9) was inactive. This suggests that the analgesic message of SP resides within the C-terminal fragment. The analgesia caused by each peptide developed more rapidly but did not last as long as that after central injection of β-endorphin. In separate experiments, 2 μg SP injected ICV increased blood pressure and decreased heart rate. The analgesic, bradycardic and pressor responses to central administration of SP were opposite to effects of peripherally administered SP, described previously. These results indicate that the effect induced by SP depends upon its specific neuroanatomical site of action.

Comparison of the bronchoconstrictor and cardiovascular effects of some tachykinins in guinea pigs

The effects of three tachykinins [substance P (SP), physalaemin (PH), and eledoisin-related peptide (ERP)] were investigated in anesthetized paralyzed guinea pigs. We measured airway resistance (R) and dynamic thoracic elastance (E) with a computerized technique, and blood pressure via a carotid artery. Tachykinins injected iv or intra-aortically (ia) induced dose-dependent increases in R and E, 4 times greater on iv than ia injection. They did not give rise to tachyphylaxis. As a bronchoconstrictor, PH was 5.0X and ERP 1.8X more potent than SP; time to peak response was longer for PH than for ERP and SP; and hypotensive responses, which were of similar magnitude for all three substances, lasted longest after PH. Bronchoconstrictor responses were unaltered by bilateral vagotomy, atropine, mecamylamine, and mepyramine. Morphine reduced PH-induced increases in R (P <0.01) and E (P <0.05), which were not reversed by naloxone, and capsaicin treatment 1 week before the experiments reduced both SP- and PH-induced increases in E (P <0.05). [D-Pro 2,D-Trp 7,9]-SP reduced ERP-induced increases in R and E, and [D-Arg 1,D-Pro 2,D-Trp 7,9,Leu 11]-SP reduced both SP- and PH-induced increases in R and E. We conclude that PH is the most potent bronchoconstrictor of the tachykinins tested. Tachykinin-induced bronchospasm is ‘non-reflex’ arising via a direct effect on airway smooth muscle; the release of histamine, acetylcholine, or other tachykinins is not involved in the responses. [D-Pro 2,D-Trp 7,9]-SP is more effective at SP-E receptors, and [D-Arg 1,D-Pro 2,D-Trp 7,9,Leu 11]-SP at SP-P receptors; both types of receptor are located all along the airways.

Occurrence and distribution of substance P-related immunoreactivity in the brain of adult lampreys, Petromyzon marinus and Entosphenus tridentatus

The occurrence and distribution of substance P (SP)-related immunoreactivity were examined in the adult brains of two species of lampreys, Petromyzon marinus and Entosphenus tridentatus, by using the PAP technique and three different anti-SP sera (anti-SP#1, anti-SP#2, and anti-SP#3). (1) In both species of lampreys, anti-SP#1 and anti-SP#2 yielded positive reactions in the brain, while there was no, or slight immunoreaction there to anti-SP#2. The positive reactions toward anti-SP sera in the lamprey brain were not eliminated, or insufficiently reduced by preabsorption with SP, but the were completely abolished by preabsorption with eledoisin-related peptide. Thus, SP-positive material in the lamprey brain is more closely related, in terms of immunological determinants, to eledoisin than to SP. (2) In Petromyzon, SP-positive perikarya were found in the ventrolateral telencephalon and the ventral hypothalamus, whereas in Entosphenus they were found in the ventral thalamus, tegmentum motoricum mesencephali (two locations), and rostral rhombencephalon, as well as in the above-mentioned two regions. Nevertheless, the distributions of SP-positive fibers in the regions of the brain other than the neurohypophysis were very similar between the two species: SP-positive fibers were found at many locations of the brain, and were especially rich in the periventricular subependymal zone of the ventral telencephalon and in the diencephalon, preoptic area, hypothalamus, and interpeduncular nucleus. (3) In Petromyzon, a heavy accumulation of positive fibers was observed in the rostral part of the anterior neurohypophysis, whereas in Entosphenus no such fibers were observed there. These results clearly suggest the presence of a neuronal system of unknown function containing a SP-related peptide in the brain of lampreys.

Effects of tachykinins on gastric acid and pepsin secretion and on gastric outflow in the Atlantic cod, Gadus morhua

Gastric acid and pepsin responses to substance P, physalaemin, eledoisin, and an eledoisin-related peptide, [Lys6]eledoisin-(6-11), were measured in gastrically and intestinally perfused cods. The intestinal perfusion maintains water balance and inhibits drinking. During basal conditions acid secretion was stimulated (approximately equal to 25%) by low doses (less than 0.13 nmol X kg-1 X h-1) of physalaemin and eledoisin. High doses (greater than 16 nmol X kg-1 X h-1) were inhibitory. Median and very high doses of substance P and eledoisin-related peptide, respectively, tended to stimulate acid secretion. All tachykinins were extremely efficacious pepsigogues. Physalaemin and eledoisin were the most potent (D50 approximately 10(-10) mol X kg-1 X h-1) but produced fading and submaximal responses at high doses. The fading persisted despite endogenous acidification produced by histamine stimulation. Relative to physalaemin, the potencies of substance P and eledoisin-related peptide were 0.04 and 0.001. The results suggest that some tachykinin may be a physiological stimulator of pepsin secretion and that the effect on acid secretion results from activation of both stimulatory and inhibitory pathways. The inhibitory component probably includes a cholinergic link. Gastric volume outflow increased during infusion of physalaemin, eledoisin, and (slightly) substance P. The response, which was not related to acid secretory rate (and conceivably not to volume secretion), suggests that a tachykinin may be involved also in the regulation of drinking.

Response of splanchnic-driven neurons to substance P and eledoisin-related peptide

The effects of iontophoretically applied substance P (SP) and eledoisin-related peptide (ERP) on the extracellularly recorded activity of spontaneous or d, l-homocysteic acid (DLH)-driven thoracic (T7–T8) spinal neurons, identified by orthodromic activation by the greater splanchnic nerve, were examined in chloralase/urethane anesthetized cats. Of 24 neurons tested, SP and/or ERP (18–120 nA) produced a weak (ca 30%) excitatory effect on 5 neurons, a weak inhibitory effect on 9 neurons, and no effect on the remaining neurons. When compared to the action of either DLH or GABA, we found both the excitatory and inhibitory effects of SP and/or ERP were delayed and prolonged. These data do not support a role for SP as a major neurotransmitter in spinal circuits in which visceral (splanchnic) afferents participate.

Tissue Plasminogen Activator Release In Vivo in Response to Vasoactive Agents

Release of tissue plasminogen activator into the circulation of rats in response to intravascular injections of vasoactive agents is studied by using a sensitive and specific clot lysis assay. Intra-arterial bradykinin elicits a rapid and transient rise in circulating plasminogen activator, which is maximum within one minute and is cleared within four to eight minutes. The plasminogen activator is fibrin dependent and is neutralized by an antiserum to human tissue-type plasminogen activator. Bradykinin is 1,000-fold more potent than the other agonists tested, which include histamine, norepinephrine, epinephrine, eledoisin-related peptide, arginine-vasopressin, lysine-vasopressin, desmopressin acetate, carbachol, and acetylcholine. Potency of bradykinin is related to its amino acid sequence. Sequential infusions of bradykinin produce a tachyphylactoid response that could be overcome by increasing the dose of the sequential bradykinin challenge. It is concluded that the characteristics of the responses to bradykinin and other agents in vivo differ significantly from those observed in isolated tissue preparations.

Tissue plasminogen activator release in vivo in response to vasoactive agents

Release of tissue plasminogen activator into the circulation of rats in response to intravascular injections of vasoactive agents is studied by using a sensitive and specific clot lysis assay. Intra-arterial bradykinin elicits a rapid and transient rise in circulating plasminogen activator, which is maximum within one minute and is cleared within four to eight minutes. The plasminogen activator is fibrin dependent and is neutralized by an antiserum to human tissue- type plasminogen activator. Bradykinin is 1,000-fold more potent than the other agonists tested, which include histamine, norepinephrine, epinephrine, eledoisin-related peptide, arginine-vasopressin, lysine- vasopressin, desmopressin acetate, carbachol, and acetylcholine. Potency of bradykinin is related to its amino acid sequence. Sequential infusions of bradykinin produce a tachyphylactoid response that could be overcome by increasing the dose of the sequential bradykinin challenge. It is concluded that the characteristics of the responses to bradykinin and other agents in vivo differ significantly from those observed in isolated tissue preparations.

Strychnine-like action of the convulsant barbiturate, CHEB

The effect of 5-(2-cyclohexylideneethyl)-5-ethyl barbituric acid (CHEB) on the isolated spinal cord of the immature rat was examined using extracellular recording. At concentrations less than 20 μM CHEB increased the monosynaptic reflex (MSR) but depressed the reflex at greater concentrations (30–100 μM). At concentrations which enhanced the monosynaptic reflex, CHEB reduced the responses of motoneurones to glycine and to a lesser extent to those of l-glutamate. In the presence of strychnine (5 μM), which enhanced both mono- and polysynaptic reflexes, CHEB produced only slight enhancement of the monosynaptic reflex. At concentrations of 30–100 μM the responses to γ-aminobutyric acid (GABA), glycine, l-glutamate and eledoisin-related peptide (ERP a substance P and analogue) were all reduced. At these concentrations CHEB directly depolarised the motoneurone membrane. Increases in [Mg 2+] 0, which reduced spontaneous activity, blocked the enhancement, by CHEB, of the monosynaptic reflex. The actions of CHEB in small doses may be due therefore to its ability to block the action of glycine and thus block tonic inhibition.

Acute effects of lead at central synapses in vitro

The acute effects of lead in the rat CNS in vitro were studied on synaptic transmission in the isolated hemisected spinal cord from newborn rats and on the transport of exogenous GABA, acetylcholine and cis-3-aminocyclohexane car☐ylic acid (ACHC) from slices of cerebral cortex from adult rats. Lead had quite variable effects on monosynaptic reflexes and synaptic potentials. When it occurred, the depression of synaptic transmission by lead (typically at 18.5 μmol/liter of added lead acetate) was reversible provided exposure times were less than 15 min; furthermore, depression could be antagonised by increasing the external calcium concentration. Lead had no effect on the postsynaptic responses of motoneurons to the putative transmitters l-glutamate, GABA and glycine or to eledoisin-related peptide. The effects of lead on uptake and release of exogenous GABA and ACHC were dependent on the perfusion buffer employed: minimal effects were seen in solutions buffered with either phosphate or carbonate. When Tris HCl was used as buffer, lead inhibited the uptake of GABA and potentiated the spontaneous release of GABA with anEC 50 = 50 μmol/liter as added lead acetate. In Tris HCl buffer, lead acetate (100 μmol/liter) produced a two-fold enhancement in the spontaneous release of acetylcholine under conditions where choline and acetylcholine re-uptake was blocked by hemicholinium. The availability of free lead cations in solution is highly dependent on the concentrations of other ions (particularly phosphates) and the pH. Under the appropriate conditions, lead can inhibit CNS synaptic function acutely in a manner consistent with lead competing with calcium ions in transmitter release processes as has been established for acetylcholine release at peripheral synapses.

Effects of glutamate, substance P and eledoisin-related peptide on solitary tract neurones involved in respiration and respiratory reflexes

Recent studies have implicated glutamate and substance P in synaptic transmission in the nuclei tractus solitarii and in central regulation of cardiorespiratory functions. Consequently, in chloralose-anaesthetized cats that were artificially ventilated, we examined the effects of the microiontophoretic application of both chemicals (and the substance P homologue, eledoisin-related peptide) on single neurones of the nuclei tractus solitarii implicated in the control of respiration and respiratory tract reflexes. These neurones were functionally identified as either respiratory neurones or presumed reflex interneurones, and showed functional properties comparable to those previously documented for each of these two types. The iontophoretic application of glutamate produced an excitation of rapid onset in 23 or 25 reflex interneurones tested, but the respiratory neurones showed a differential sensitivity: one type ( n = 32) was “glutamate-sensitive” and showed rapid excitation with glutamate applications of less than 30 nA, the other type of respiratory neurone ( n = 26) was termed “glutamate-insensitive” since it either showed excitation only with applications of 60 nA or more or showed no response even with currents up to 94 nA. Each neurone studied was clearly of one type or the other. Glutamate could increase the number of spikes per rhythmic burst and the burst duration of respiratory neurones, it facilitated evoked activity in the reflex interneurones and in those respiratory neurones having a superior laryngeal nerve or vagus nerve afferent input, and the magnitude of the excitatory responses to glutamate varied directly with the amount of ejecting current. Substance P and eledoisin-related peptide also had exeitatory effects on respiratory neurones and reflex interneurones, but compared with glutamate-induced effects the excitation was slower in onset and more prolonged in after-discharge. Both rhythmic and evoked activity could be facilitated, and the magnitude of the effect varied directly with the magnitude of the ejecting current. In showing that both glutamate and substance P (and its analogue, eledoisin-related peptide) have excitatory effects on the activity of respiratory neurones and reflex interneurones, this study provides evidence suggesting that these neurones have receptors for these neural chemicals, supportive of a role for each chemical in the regulation of respiration and respiratory tract reflexes.

Pharmacological characterisation of two tachykinin binding sites in the rat cerebral cortex

The pharmacological properties of two types of tachykinin receptor were characterised on rat cortical synaptosomes using 125I-Bolton Hunter substance P ( 125I-BHSP) or with 125I-Bolton Hunter eledoisin ( 125I-BHE). Shorter SP C-terminal fragments, such as SP (6–11) or (pGlu)-SP (6–11), were more potent than SP itself or longer SP C-terminal fragments in competing for 125I-BHE binding; their efficacy was comparable to that of eledoisin. In contrast, longer SP C-terminal fragments exhibited a higher affinity than shorter ones for the 125I-BHSP binding sites as previously reported. SP N-terminal fragments were devoid of activity on either type of binding sites. SP methyl ester inhibited 125I-BHSP binding but was without effect on 125I-BHE binding whilst, DiMe-C7, a metabolically stable tachykinin analog, had the opposite selectivity. Eledoisin related peptide (ERP) was less effective than either SP or eledoisin on 125I-BHSP and 125I-BHE binding sites respectively. Finally, the undecapeptide or octapeptide SP antagonists, which are weak inhibitors of 125I-BHSP binding, had negligable activity on 125I-BHE binding sites.

Comparative specificity and kinetic studies on porcine calpain I and calpain II with naturally occurring peptides and synthetic fluorogenic substrates.

Homogeneous porcine calpain (Ca2+-dependent cysteine proteinase) was found to hydrolyze a variety of peptides and synthetic substrates. Leu-Trp-Met-Arg-Phe-Ala, eledoisin-related peptide, alpha-neoendorphin, angiotensin I, luteinizing hormone-releasing hormone, neurotensin, dynorphin, glucagon, and oxidized insulin B chain were cleaved with a general preference for a Tyr, Met, or Arg residue in the P1 position preceded by a Leu or Val residue in the P2 position. No great difference in specificity was found between low-Ca2+-requiring calpain I and high-Ca2+-requiring calpain II. 4-Methylcoumaryl-7-amide (MCA) derivatives having a Leu(or Val)-Met(or Tyr)-MCA or a Leu-Lys-MCA sequence were also cleaved by either calpain I or calpain II with preference for Leu over Val by a factor of 9 to 16. Calpains I and II showed similar but not identical kinetic behavior for individual substrates. The Km and kcat values ranged from 0.23 to 7.08 mM and 0.062 to 0.805 s-1 for the calpains, while kcat/Km values for the calpains were only 1/433 to 1/5 of those for papain with a given substrate. With succinyl-Leu-Met(or Tyr)-MCA, calpains I and II were half-maximally activated at 12 and 260 microM Ca2+, respectively, and competitively inhibited by leupeptin (Ki = 0.32 microM for I and 0.43 microM for II) or antipain (Ki = 1.41 microM for I and 1.45 microM for II). Thus, this is the first report describing the specificity and kinetics of calpains I and II.

Effect of substance P on exocrine secretion by rat submandibular gland cells.

The effects of the undecapeptide, substance P(SP), on the secretion of mucin and proteolytic enzymes from dispersed cells of the rat submandibular gland were studied. The peptide, at a concentration of 1 X 10(-7) M, stimulated the release of 31.9 +/- 3.0% (mean +/- SEM) of intracellular mucin over 40 min, compared with 12.5 +/- 1.5% in untreated controls (p less than 0.01). This effect was duplicated by the homologous peptides, physalaemin, and eledoisin-related peptide. Substance P action was not affected by pre-incubation of cells with phentolamine or propranolol and was therefore independent of adrenergic stimulation. Furthermore, SP did not enhance the intracellular concentrations of cyclic AMP or cyclic GMP, confirming that cyclic nucleotides were not involved in its stimulus-secretion coupling mechanism. The isoproterenol-stimulated secretion of mucin from dispersed cells was reduced to 75.7% of the normal response (p less than 0.01) after a brief exposure to SP. This inhibitory effect was probably mediated by intracellular events rather than by direct effects on cell surface receptors. However, mucin release after treatment with SP followed by norepinephrine (NE) was 161% of that caused by NE alone (p less than 0.01) and may reflect an additive response to the independent stimulation of SP and NE receptors. Substance P and related peptides had no effect on arginine esterase secretion in the experimental model, although a response was elicited by alpha- and beta-adrenergic agonists. It is, therefore, proposed that serous cells of the granular convoluted tubule in the rat submandibular gland lack substance P receptors.

Substance P, injected intrathecally, antagonizes the spinal antinociceptive effect of morphine, baclofen and noradrenaline

The effect of substance P on the antinociceptive effect of morphine, baclofen and noradrenaline in the spinal cord was examined in the tail-flick and hot plate tests, after intrathecal administration. Substance P (5–20 μg) produced a dose-related antagonism of the effect of all three agents, which persisted for the entire time-course of the antinociceptive effect in each case. The rank order of potency of substance P and related peptides in antagonizing the antinociceptive effect of morphine, was substance P > physalaemin > eledoisin > eledoisin-related peptide. A similar order of potency was observed against noradrenaline, except that physalaemin appeared to be the most potent. The intrathecal administration of these peptides did not alter reaction latencies in the tail-flick test when baseline values were 2–3 sec, but produced a significant decrease in latency (hyperalgesia) when baseline values were 6–8 sec. There was a slight increase in reaction latency in the hot plate test. The specificity of the antagonism was examined by determining the effect of phentolamine on the antinociceptive effect of morphine and baclofen. Although phentolamine (30 μg) produced comparable hyperalgesia to substance P, it did not significantly alter the antinociceptive effect of morphine or baclofen. These results suggest that alterations in the function of substance P in the spinal cord may contribute to the spinal antinociceptive effects of morphine, baclofen and noradrenaline. The effects of substance P on nociception in the spinal cord appear to be mediated by substance P type receptors.

The effect of calcium ions on the responses to motoneurons to substance P and eledoisin-related peptide in the toad and rat spinal cord

The effects of changes in the external calcium ion concentration [Ca 2+] 0 on segmental reflexes and the responses of motoneurons to bath applied agonists have been studied in the toad and rat spinal cords in vitro. Reducing [Ca 2+] 0 enhanced polysynaptic reflexes in the toad, with maximal discharges occurring at 0.3 mM. Monosynaptic reflexes in the rat were reduced by lowering [Ca 2+] 0. Responses of toad motoneurons to substance P and eledoisin-related peptide were enhanced by lowering [Ca 2+] 0, maximum responses occurring at 0.3 mM. Lowering [Ca 2+] 0 also enhanced responses to l-glutamate but the effect was smaller and less consistent. This effect of Ca 2+ was abolished by the addition of tetrodotoxin to the bathing solution. Toad motoneuron responses to γ-aminobutyrate and glycine were not affected by alterations in [Ca 2+] 0. Rat motoneuron responses to substance P and eledoisin-related peptide were also enhanced by reductions in [Ca 2+] 0 but the effect was more pronounced in younger (<5 days post partum) than older (5–10 days post partum) animals. These results are consistent with the idea that motoneuron responses to peptides in normal solutions result from activation of receptors on both motoneurons and interneurons: enhancement of the responses by lowering [Ca 2+] 0 results from the potentiation of the transynaptic component.

Hyperalgesia produced by intrathecal substance P and related peptides: desensitization and cross desensitization.

The hyperalgesic effect of intrathecally administered substance P (SP), physalaemin, eledoisin and eledoisin-related peptide (ERP) was investigated in the rat tail flick test. Hyperalgesia produced by SP (2.5-15 micrograms, 1.9-11 nmol) was maximal 10-20 min after injection, lasted 30 min and was dose-related. The effect was mimicked by all of the peptides examined. The rank order of potency was physalaemin greater than SP greater than eledoisin greater than ERP. Desensitization to the hyperalgesic effect of SP was produced by three repeated intrathecal injections. Rats desensitized to SP no longer responded to physalaemin or ERP, indicating cross-desensitization. Phentolamine continued to produce hyperalgesia following such desensitization. The demonstration of a hyperalgesic effect for SP provides further support for a role for SP in nociceptive transmission. The receptor mediating this effect appears to be a SP-P subtype. Cross-desensitization between peptides suggests an action on the same receptor.

A study of [d‐Pro2, d‐Phe7, d‐Trp9]‐substance P and [d‐Trp7,9]‐substance P as tachykinin partial agonists in the rat colon

Two substance P (SP) analogues, [D-Pro2, D-Phe7, D-Trp9]-SP (DPDPDT) and [D-Trp7,9]-SP (DT79), previously described as tachykinin antagonists, have been shown to contract the rat colon muscularis mucosae preparation. The maximum response exhibited by these analogues was about 30% that of the SP maximum, suggesting that they were acting as partial agonists relative to SP. The responses to DPDPDT were unaffected by pretreatment with mepyramine, methysergide or [Sar1, Ile5, Ala8]-angiotensin II, which abolished the responses to histamine, 5-hydroxytryptamine (5-HT) and angiotensin II, respectively. Methysergide also did not affect the responses to DT79; the other antagonists were not tested against this analogue. Indomethacin and cimetidine also had no inhibitory effect. Atropine (2 microM) was present in all experiments to prevent indirect muscarinic effects. Phenoxybenzamine did not affect the dose-response curves to SP, eledoisin-related peptide (ERP), kassinin, eledoisin or physalaemin, nor did it affect the responses to individual doses of DPDPDT or DT79. However, in the absence of atropine, it shifted the carbachol dose-response curve markedly to the right, and reduced its maximum. The tachykinin antagonist [D-Pro4, D-Trp7,9,10]-SP4-11 reduced the responses to individual matched doses of DPDPDT, DT79 and SP to the same degree, whilst leaving responses to 5-HT or angiotensin II unaffected. This suggested that DPDPDT and DT79 were acting at the same receptor as SP. The inhibitory effects of DPDPDT on responses to SP, ERP and kassinin, and that of DT79 on responses to SP, were analysed. All four combinations yielded data compatible with an interaction at only one receptor, although DPDPDT appeared slightly more potent at inhibiting responses to kassinin. The results are discussed in the light of the proposed existence of multiple tachykinin receptor subtypes. The possible influence of differential metabolism of tachykinin analogues is also considered.

Control of nasal vasculature and airflow resistance in the dog.

Nasal vascular and airflow resistances have been measured in dogs, simultaneously on both sides separately. Vascular resistance was measured either by constant flow perfusion of the terminal branch of the maxillary artery (which supplies, via the sphenopalatine artery, the nasal septum, most of the turbinates and the nasal sinuses) or by measuring blood flow through this artery, maintained by the dog's own blood pressure. Airflow resistance was assessed by inserting balloon-tipped endotracheal catheters into the back of each nasal cavity via the nasopharynx, and measuring transnasal pressure at constant airflow through each side of the nose simultaneously. Preliminary experiments indicated that there was 5-10% collateral anastomosis between the two sides. Close-arterial injection of drugs showed different patterns of response. Adrenaline, phenylephrine, chlorpheniramine and low doses of prostaglandin F2 alpha increased vascular resistance and lowered airway resistance. Salbutamol, methacholine and histamine lowered vascular resistance and increased airway resistance. Dobutamine decreased airway resistance with a small increase in vascular resistance. Prostaglandins E1, E2 and F2 alpha (high dose) decreased both vascular and airway resistances. Substance P, eledoisin-related peptide and vasoactive intestinal polypeptide lowered vascular resistance with little change in airway resistance. The results are interpreted in terms of possible drug actions on precapillary resistance vessels, sinusoids and venules, and arteriovenous anastomoses. It is concluded that nasal airway resistance cannot be correlated with vascular resistance or blood flow, since the latter has a complex and ill-defined relationship with nasal vascular blood volume.