Effects of the substance P antagonist, (D-Arg1, D-Pro2, D-Trp7,9, Leu11)-SP on the miotic response to substance P, antidromic trigeminal nerve stimulation, capsaicin, prostaglandin E1, compound 48/80 and histamine

The effects of the substance P analogue (D-Arg1, D-Pro2, D-Trp7,9, Leu11)-SP on the ocular inflammatory responses (miosis, vasodilation, protein leakage into the aqueous humour and eye pressure rise) to antidromic trigeminal nerve stimulation (trigeminal stimulation), intracameral injections of substance P (SP), capsaicin, prostaglandin E1 (PGE1), compound 48/80 and histamine were investigated in albino rabbits. The effects of nerve blockade with tetrodotoxin and blockade of histamine receptors on the responses to compound 48/80 and histamine were also investigated. Histamine H1 receptors were blocked with clemastin and H2 receptors with cimetidin. Formation of endogenous prostaglandins was prevented with indomethacin. The pupil size and the eye pressure were measured. The aqueous humour was collected immediately after the animal was killed, and analyzed for protein concentration. (D-Arg1, D-Pro2, D-Trp7,9, Leu11)-SP had no significant miotic effect, but tended to cause a break-down of the blood-aqueous barrier. Miosis caused by SP, trigeminal stimulation, capsaicin, PGE1, compound 48/80 or histamine was blocked by (D-Arg1, D-Pro2, D-Trp7,9, Leu11)-SP. Histamine miosis was significantly reduced by blockade of nerve conduction or histamine receptors, while miosis caused by compound 48/80 was not. Nerve blockade abolished the rise in intraocular pressure caused by compound 48/80. Our results indicate that (D-Arg1, D-Pro2, D-Trp7,9, Leu11)-SP is a specific SP blocker in the sphincter pupillae muscle. They are strong evidence for the hypothesis that trigeminal stimulation and capsaicin cause miosis by release of SP or a related substance (SPLI), and it seems likely that the miosis caused by PGE1 and compound 48/80 is also caused by SPLI release. Histamine miosis is probably mediated both by SP receptors and histamine receptors in the pupillary sphincter muscle.     

Effects of intranigral substance P and neurokinin A on striatal dopamine release--I. Interactions with substance P antagonists.

The functional role of striatonigral neurokinins were studied by analysing the effects of intranigral injections of substance P and neurokinin A on the extracellular level of dopamine and dihydroxyphenylacetic acid in the striatum, as measured by in vivo microdialysis in rats. Two substance P antagonists, substance P D-Pro2 D-Trp7,9 and substance P D-Arg1 D-Trp7,9 Leu11 were tested and analysed for their ability to block the neurokinin effects. Unilateral injections of substance P (0.00007-7.0 nmol injected in 0.2 microliter) as well as neurokinin A (0.009-9.0 nmol) into the substantia nigra, pars reticulata of halothane anaesthetized rats produced long-lasting increases in ipsilateral striatal dopamine and dihydroxyphenylacetic acid levels. The dose-response relationship for substance P on dopamine was biphasic, with maximal effects occurring after the middle dose (0.007-0.07 nmol). The dose-response relationship for neurokinin A was monophasic. Intranigral injections of substance P D-Pro2 D-Trp7,9 (0.07-0.7 nmol) or substance P D-Arg1 D-Trp7,9 Leu11 (0.07-0.7 nmol) produced a decrease in striatal dopamine, but an increase in striatal dihydroxyphenylacetic acid. At a low dose (0.07 nmol) substance P D-Pro2 D-Trp7,9 enhanced the dopamine increase produced by intranigral substance P (0.07 nmol) or neurokinin A (0.09), while at a high dose (0.7 nmol) it blocked both substance P and neurokinin A effects. Both doses of substance P D-Arg1 D-Trp7,9 Leu11 (0.07 and 0.7 nmol) blocked the substance P- but not the neurokinin A-induced increase in striatal dopamine. Immunohistochemical analysis revealed that high doses of substance P (7.0 nmol) and neurokinin A (0.9 and 9.0 nmol), as well as substance P D-Pro2 D-Trp7,9 and substance P D-Arg1 D-Trp7,9 Leu11 (0.07 and 0.7 nmol), induced a restricted loss of tyrosine hydroxylase in dendrites and cells, and neuropeptide K in terminals, at the site of injection. Further analysis shows that co-administration of substance P (0.07 nmol) or neurokinin A (0.09 nmol) did not modify the extent of the depletion of both immunoreactivities induced by substance P D-Arg1 D-Trp7,9 Leu11 (0.7 nmol). The extent of the effect produced by substance P D-Arg1 D-Trp7,9 Leu11 (0.7 nmol) was, however, smaller than the spread of intranigral injection of [125I]Bolton-Hunter-labelled substance P D-Arg1 D-Trp7,9 Leu11, and it is suggested that the "neurotoxic" effects of the substance P antagonists are not primarily involved in their abilities to inhibit striatal dopamine release and block the stimulation of dopamine after intranigral substance P and neurokinin A.(ABSTRACT TRUNCATED AT 400 WORDS)     

Neural actions of several substance P antagonists in the rat spinal cord

Four substance P (SP) antagonists were tested on anaesthetized rats, by injecting 8 microgram amounts into the spinal cord (T8-T9), and by observing their effects on the hypothalamo-neurohypophysial responses to a presumably painful stimulus, the superfusion of the hepatic portal vein with 1 microM bradykinin. Only two antagonists, the new D-Pro4,D-Trp7,9,10,Val8-SP4-11 and D-Pro4,D-Trp7,9,10-SP4-11 were capable of inhibiting the responses by 50-60%, the former compound having 3 times less agonistic activity. The results suggest that substitution of the aromatic phenylalanine by the non-polar valine in position 8 may significantly improve the overall characteristics of neurally active SP antagonists.     

The pharmacological profile of a substance P (SP) antagonist. Evidence for the existence of subpopulations of SP receptors

The purpose of this study was to evaluate the pharmacological properties of a substance P (SP) analogue [D-Arg, D-Pro, D-Trp, Leu]SP as an SP antagonist. This analogue, blocked the SP-induced contractions of the isolated guinea-pig ileum and the rat urinary bladder and it exhibited no spasmogenic activity on these preparations. The affinity constant (pA2) for [D-Arg, D-Pro, D-Trp, Leu]SP versus SP was 6.31 on the guinea-pig ileum preparation and 5.30 on the rat urinary bladder preparation. The slopes of the regression lines of the Schild plots were close to unity. These data indicate that [D-Arg, D-Pro, D-Trp, Leu]SP blocks SP receptors in a simple competitive manner and suggest that there are at least two subpopulations of SP receptors. The contractions caused by the closely related tachykinins eledoisin and physalaemin were also blocked by the SP analogue. However, the slopes of the regression lines were significantly different from unity. Moreover, when tested on the hamster urinary bladder, which contracts at low concentrations of eledoisin but is rather insensitive to physalaemin and SP, [D-Arg, D-Pro, D-Trp, Leu]SP did not block the contractile actions of eledoisin or of physalaemin and SP. Compared to SP eledoisin and physalaemin may bind to SP receptors in a different manner. Eledoisin also seems to interact with receptors different from the SP receptors.     

Antagonism by (D-Pro2, D-Trp7,9)-substance P of the cerebrovascular dilatation induced by substance P

The effects of (D-Pro2, D-Trp7,9)-substance P, a structural analogue of substance P, were examined in two models on cerebrovascular responses to substance P(SP) in cats; in vitro using segments of the middle cerebral artery and in situ by microapplication of the peptides close to pial arterioles. (D-Pro2, D-Trp7,9)-SP in concentrations up to 6.6 x 10(-6) M was without significant effect upon isolated middle cerebral arteries under normal conditions and in arteries contracted with prostaglandin F2 alpha. SP caused concentration-dependent relaxations of middle cerebral arteries contracted by prostaglandin F2 alpha (mean +/- SE; EC50: 2.0 +/- 1.6 x 10(-9) M). The presence of (D-Pro2, D-Trp7,9)-SP shifted the concentration-response curve of SP towards higher concentrations without significantly effecting the maximum response of the arteries to SP. A relaxation by 24.2 +/- 4.0% (n = 6) was obtained in prostaglandin F2 alpha contracted arteries by increasing the potassium concentration with 2 mM in the buffer solution. This response to potassium was unaltered in the presence of 6.6 x 10(-6)M of (D-Pro2, D-Trp7,9)-SP (25.0 +/- 7.1%, n = 5). Perivascular microapplication of SP around individual pial arterioles in situ effected dose-dependent increases in vascular calibre (mean response 14.5 +/- 2% with SP, 10(-7)M). The concomitant perivascular administration of (D-Pro2, D-Trp7,9)-SP (6.6 x 10(-6)M), which alone did not alter the arteriolar calibre, attenuated significantly the cerebrovascular response to SP (mean response 1.5 +/- 3.2%). On the basis of the agonist-antagonist relation found, these observations point to the possibility of a specific SP receptor site in cerebral arteries and arterioles.     

Do local vasomotor effects elicit the motor deficits induced by intrathecally applied substance P antagonists in the rat?

The intrathecal application of the substance P (SP) antagonists [D-Pro2,D-Trp7,9]SP (DPDT) and [D-Arg1, D-Pro2, D-Trp7,9, Leu11]SP (DAPTL) to the lumbar region of intact, freely moving rats produced laming of the hindlimbs at doses of 0.375 nmol and above, and 1.5 nmol and above, respectively. In addition, the administration of DPDT (doses of 25 and 0.18 nmol) and DAPTL (25 and 0.6 nmol) produced a powerful constriction of the dorsal median spinal vein (DMSV) in decerebrated, unanaesthetised rats. Intrathecal SP (25 or 1.0 nmol) had a similar action on the spinal circulation to DPDT and DAPTL, though laming was first observed at doses of 30 nmol and higher. This suggests that intrathecally applied SP antagonists do not elicit laming by causing an obstruction of the venous drainage of the spinal cord. Disturbances of the spinal circulation could, however, influence the results of behavioural or physiological experiments in which SP or its analogues are administered intrathecally.     

Interaction of substance P with dispersed pancreatic acinar cells from the guinea pig. Relationships between structure, binding and biological activity

Binding of 125I-[Tyr8]-SP to isolated pancreatic acinar cells was inhibited in a concentration-dependent way by SP, [Tyr8]-SP and longer C-terminal fragments of SP. SP6-11 was the shortest sequence to bind significantly to SP-receptors as well as to stimulate amylase release from dispersed pancreatic acini. SP7-11 and shorter fragments did not inhibit binding of 125I-[Tyr8]-SP and did not stimulate secretion of amylase significantly. SP augmented the stimulatory effect of cholecystokinin on amylase release. Two SP-antagonists, [D-Pro2, D-Trp7,9]-SP and [D-Pro2,4, D-Lys3, D-Gln5,6, D-Trp7,9]-SP inhibited binding of 125I-[Tyr8]-SP in a concentration dependent manner and tended at a high concentration to reduce release of amylase evoked by submaximal concentrations of SP.     

Antinociceptive and neurotoxic actions of substance P analogues in the rat's spinal cord after intrathecal administration

Intrathecal administration of both (D-Pro2,D-Trp7,9)-substance P (DPDT) and (D-Arg1,D-Trp7,9,Leu11)-substance P (DADTL) elicited antinociception in hot-plate and tail-flick test, with DADTL as the most potent. The animals injected with 2.0 micrograms DADTL, and several animals administered with DPDT at the same dose, developed bilateral motor blockade of the hind-legs, persisting for up to 3 days after DADTL. The effect of DPDT appeared to be reversible at this dose. On histopathological examination it was found that these animals with persistent paralysis had widespread neuronal necrosis in the lumbar region of the spinal cord. It is concluded that the peptides have antinociceptive effects after the intrathecal administration in rats, but that there is a small margin between the dose producing this effect and that causing irreversible toxic reactions in the spinal cord.     

Observations on the actions of substance P and [D-Arg1,D-Pro2,D-Trp7,9,Leu11)substance P on single neurons of the guinea pig submucous plexus

Intracellular recordings were made from neurons of the guinea pig submucosal plexus and the effects of substance P and the substance P analogue [D-Arg1,D-Pro2,D-Trp7,9,Leu11]substance P were examined. Substance P (20-200 nM) depolarized all submucosal neurons; these depolarizations were shown to be due to a decrease in the resting (or "leak") potassium conductance of the membrane. In approximately 50% of the 46 neurons tested, superfusion with [D-Arg1,D-Pro2,D-Trp7,9,Leu11]substance P (0.2-20 microM) produced a dose-dependent membrane hyperpolarization. This hyperpolarization was prevented by the alpha 2-adrenoceptor antagonist idazoxan (300 nM) or by concentrations of cobalt which abolished all spontaneous and evoked synaptic potentials, indicating that it resulted from release of noradrenaline from sympathetic nerve terminals. [D-Arg1,D-Pro2,D-Trp7,9,Leu11]substance P depressed the amplitude of the three synaptic potentials recorded from submucosal neurons; the concentrations that caused 50% of the maximal inhibition of the fast excitatory postsynaptic potential, the inhibitory postsynaptic potential, and slow excitatory postsynaptic potential were 40 microM, 600 nM and 20 microM, respectively. When idazoxan was present, the substance P analogue was less effective in depressing the amplitudes of the fast and slow excitatory synaptic potentials suggesting that much of its presynaptic inhibition also resulted from release of noradrenaline. These results provide evidence that [D-Arg1,D-Pro2,D-Trp7,9,Leu11]substance P releases noradrenaline from sympathetic nerves in the submucosal plexus. One effect of this is a membrane hyperpolarization; another is a presynaptic inhibition of transmitter release. These actions much limit the usefulness of this "substance P antagonist" in efforts to show that synaptic potentials, such as the slow excitatory synaptic potential, are mediated by substance P.     

Sympathetic control of substance P releasing enteric neurones in the guinea pig ileum

The contractile response of the isolated guinea-pig ileum to cholecystokinin octapeptide (CCK-8) that remained in the presence of atropine was greatly inhibited by the substance P antagonist D-Pro2,D-Trp7,9-substance P. This indicates that the atropine-resistant contraction to CCK-8 is mediated by the release of substance P from enteric neurones. Activation of alpha-adrenergic receptors by noradrenaline, clonidine or mesenteric sympathetic nerve stimulation inhibited the atropine-resistant contraction to CCK-8 but did not affect the contractile effect of substance P. It is concluded that alpha-adrenergic receptors exert an inhibitory influence on the release of substance P from enteric neurones.     

The effects of substance P and calcitonin gene-related peptide on the efflux of endogenous glutamate and aspartate from the rat spinal dorsal horn in vitro.

Bath applied SP (2 x 10(-7) to 5 x 10(-7) M) produced a significant increase in the concentration of glutamate in the spinal slice perfusate, whereas the efflux of aspartate increased only with a higher concentration of SP (5 x 10(-6) M). The enhancement of the basal efflux of glutamate persisted in the absence of external Ca2+, but the effect was blocked by (D-Arg1, D-Pro2, D-Trp7,9, Leu11)-SP, a SP analogue claimed to be an antagonist of synthetic SP. Calcitonin gene-related peptide (CGRP 10(-7) M) produced a significant increase in the concentrations of glutamate and aspartate in the perfusate. Neonatal capsaicin treatment prevented the SP-induced increase in the release of glutamate. In contrast, the effect of CGRP was not significantly modified by the capsaicin treatment. These results indicate that SP and CGRP are capable of modulating the basal efflux of endogenous aspartate and glutamate and this modulation may represent one of the mechanisms by which these peptides contribute to primary afferent synaptic transmission.     

Some effects of substance P on central respiratory control in rabbit pups

Respiratory effects of substance P (SP) have been studied in rabbit pups (I-30 days). Rabbits were either anaesthetized with urethane or decerebrated at mid-collicular level. Respiratory activity was measured with a pneumotachograph or in some cases as efferent phrenic nerve activity. SP applied to the exposed medulla oblongata from the dorsal side caused an increase of both tidal volume and respiratory frequency. The respiratory stimulation was more pronounced in decerebrate animals than in anesthetized ones. Moreover, this effect was most prominent in the youngest animals. A SP analogue (D-Arg1-D-Pro2, D-Trp7,9, Leu11)-SP was found to block the ventilatory effects of SP and to decrease the hypoxic response, while the hypercapnic response was preserved. The results suggest that SP is involved in the control of respiration, possibly mediating the hypoxic response, and that this role is more important in the neonatal period.     

The action of a substance P antagonist on sympathetic nerve activity in the rat

In anaesthetised rats recordings were made of sympathetic activity in renal nerves whilst studying the effects of intrathecal injection of the substance P antagonist (D-Arg1, D-Pro2, D-Trp7,9, Leu11)-substance P on the responses to, stimulation of the ventrolateral medulla, to intrathecal injection of substance P, serotonin and glutamate. All responses were abolished by the antagonist.     

Substance P in the cerebrospinal fluid-contacting nucleus contributes to morphine physical dependence in rats

The cerebrospinal fluid-contacting nucleus (CSF-CN), distributes and localizes in the ventral periaqueductal central gray (PAG) of the brainstem, which may influence actual composition of the cerebrospinal fluid (CSF) for non-synaptic signal transmission via releasing or absorbing bioactive substances. Many experiments have demonstrated that substance P (SP), a substance that is shown to be up-regulated in CSF-CN, plays an important role in the development of inflammatory pain and neuropathic pain. Thus in the present study, we hypothesize that SP in CSF-CN might contribute to morphine dependence in rats, inhibiting SP with (D-Pro2, D-Phe7, D-Trp9)-SP intracerebroventricular (i.c.v.) injection reduce chronic morphine dependence and withdrawal. Rats were repeatedly injected with morphine in five escalating doses for morphine physical dependence. Morphine withdrawal-like behavioral signs and morphine analgesia behaviors were monitored after naloxone administration following i.c.v. injection of (D-Pro2, D-Phe7, D-Trp9)-SP. And SP-expression of CSF-CN was evaluated with dual-label immunofluorescent technique on morphine withdrawal in rats. After i.c.v. treatment with (D-Pro2, D-Phe7, D-Trp9)-SP, the naloxone-precipitated withdrawal symptoms were significantly attenuated, paw withdrawal threshold/thermal withdrawal latency (PWT/TWL) were increased, and SP-expression in CSF-CN was significantly reduced than control group. SP, known a neurotransmitter/neuromodulator of nociception, has also been implicated in the signs of opioid withdrawal. This study provides the first evidence that SP in CSF-CN contributes to morphine physical dependence and withdrawal, which may provide an important and specific role in mediating the motivational aspects of opiates withdrawal via CSF - the parenchyma of the brain, and may represent a novel pharmacological route such as SP inhibitor i.c.v. injection for the control of drug abuse.     

D-Arg1, D-Trp7,9, Leu11-substance P (spantide) does not antagonize substance P-induced hyperexcitability of the nociceptive flexion withdrawal reflex in the rat

The effect of D-Arg1, D-Trp7,9, Leu11-substance P (SP) (spantide), a putative SP antagonist, on SP-induced facilitation of the flexion reflex was examined. The drugs were injected intrathecally (i.t.) in decerebrate, spinalized, unanaesthetized rats. Substance P (10 ng) caused an increase in reflex magnitude for about 5 min. Spantide (10 ng and 100 ng) also caused a facilitation of the reflex that was similar to SP. Spantide (10 ng) plus SP (10 ng) also had a similar excitatory effect. One microgram of spantide totally blocked the flexion reflex, which could not be reversed by SP, L-glutamate, L-aspartate or naloxone. It is concluded that spantide does not have an antagonistic effect on SP-induced changes in spinal reflex excitability. Some of the effects of i.t. spantide observed in behavioural studies may be due to a non-specific spinal motor block. It is suggested that the flexion reflex in the decerebrate, spinalized rat is a useful physiological model in studies of the effects of algesic and analgesic drugs at spinal level.     

Hypertonic KCI, NaCl and capsaicin intracamerally causes release of substance P-like immunoreactive material into the aqueous humor in rabbits

We have investigated release of substance P-like immunoreactivity (SPLI) into the anterior chamber of the rabbit eye evoked by stimuli which cause non-cholinergic miosis. In a recent study such miosis was reported to be blocked by the substance P analogue (D-Arg1, D-Pro2, D-Trp7,9, Leu11)-SP. Mechanical intracranial antidromic trigeminal nerve stimulation caused marked SPLI release presumably from primary sensory nerve endings in the anterior part of the eye. Intermittent stimulation for 20 min was not more effective than stimulation for 10 min. Intracameral injection of either 20 microliters 4.65 M KCI, 20 microliters 4.65 M NaCl or 100 micrograms capsaicin also caused SPLI release. Intracameral injection of 70 microliters 150 mM KCI, 28 micrograms prostaglandin E1 or 200 micrograms of compound 48/80 did not cause detectable SPLI release.     

Pharmacological characterization of four related substance P antagonist

The purpose of this pharmacological study was to further characterize 4 related substance P (SP) analogues, namely (D-Pro², D-Phe⁷, D-Trp⁹)-SP (I), (D-Pro², D-Trp^7.9)-SP (II), (D-Arg¹, D-Pro², D-Phe⁷, D-Trp⁹)-SP (III) and (D-Arg¹, D-Pro², D-Trp^7.9)-SP (IV). At a concentration of 10^-4 M they were found to have little or no smooth muscle-contracting effect on the guinea-pig ileum, analogues I and II having substantially less agonist activity than III and IV. Pretreatment with the analogues inhibited the contractile responses to SP, but not to histamine or acetylcholine. Of the 4 analogues, II was found to be the most potent SP antagonist. The contractile responses to physalaemin and eledoisin were also inhibited by analogue II. The concentration-response curves for SP were shifted in parallel to higher concentrations in the presence of the analogues. The pA₂-values derived from Schild plots were 4.61 for (I), 5.43 for (II), 4.69 for (III) and 5.11 for (IV). Except for (I) the slopes of the regression lines of the Schild plots were close to unity. The data are consistent with simple competitive antagonism over the concentration ranges investigated. Without being secretagogues per se, the analogues inhibited SP-stimulated salivary secretion in the rat. Physalaemin-stimulated secretion was inhibited by analogue II. The inhibitory effect of sequences with D-Arg¹ instead of L-Arg¹ seemed to be of longer duration. Not one of these analogues blocked the blood pressure-lowering effect of SP, which indicates the existence of more than one type of SP receptor. This study has shown that 4 related SP analogues specifically inhibit the actions of SP and structurally related peptides physalaemin and eledoisin, both in vitro and in vivo. Analogues II-IV seem to inhibit in a simple competitive manner. (D-Pro², D-Trp^7.9)-SP was the most potent of the 4 SP antagonists.     

In the eye (D-Pro2, D-Trp7,9)-SP is a substance P agonist,which modifies the responses to substance P,prostaglandin E1 and antidromic trigeminal nerve stimulation

A substance P analogue, (D-Pro², D-Trp^7,9)-SP, has been described to have SP antagonistic and SP agonistic effects in different tissues. We have investigated the effects of (D-Pro², D-Trp^7,9)-SP on the sphincter pupillae muscle, the blood aqueous barrier (BAB) and the intraocular pressure (IOP) in the albino rabbit eye. We also investigated the modifying effects of (D-Pro², D-Trp^7,9)-SP on miosis, BAB damage and IOP rise caused by SP, prostaglandin E₁ (PGE₁), capsaicin and on the miosis caused by electrical intracranial antidromic trigeminal nerve stimulation (NV stim). Endogenous PG synthesis was inhibited by systemic indomethacin i. v., cholinergic influence on the pupil size was inhibited with biperiden, i. v., adrenergic nerve influence by cervical sympathectomy just prior to the expts. Tubocurarine chloride was used to cause relaxation of striated muscles in the expts with NV stim. We found 100 μg (D-Pro², D-Trp^7,9)-SP to cause miosis, breakdown of the BAB with heavy leakage of Evans blue into the ciliary processes and aqueous humor, and a rise in IOP. At 10 μg (D-Pro², D-Trp^7,9)-SP caused slight miosis and did not inhibit the miosis caused by SP or capsaicin, but caused a significant reduction of the miotic response caused by PGE₁ and NV stim. The rise in protein concentration in the aqueous humor caused by SP or PGE₁ was slightly but significantly lower after pretreatment with (D-Pro², D-Trp^7,9)-SP. Thus (D-Pro², D-Trp^7,9)-SP was found to act as a SP agonist on the sphincter pupillae muscle, on the BAB and IOP. However, (D-Pro², D-Trp^7,9)-SP seemed to have some SP antagonistic effects on mechanisms that require sensory nerve conduction e. g. miosis caused by PGE₁ and NV stim. The antagonistic mechanism is not clear. The SP analogue may have an unspecific membrane stabilizing effect or a toxic effect or block SP receptors on the sensory nerve fibers. Such effects of (D-Pro², D-Trp^7,9)-SP may explain also why the rise in protein concentration in the aqueous humor caused by SP and PGE₁ was lower in eyes pretreated with (D-Pro², D-Trp^7,9)-SP.     

Antagonism of non-cholinergic excitatory junction potentials in the guinea-pig ileum by a substance P analogue antagonist

In the presence of atropine electrical transmural stimulation (using repetitive volleys, e.g. 3 pulses at 50 Hz applied every 4 s) of full thickness longitudinal strips of guinea-pig ileum produced non-cholinergic excitatory junction potentials (EJPs) and inhibitory junction potentials (IJPs) in the circular muscle layer. After abolition of the IJPs with apamin, the non-cholinergic EJPs clearly showed facilitation. In the presence of apamin and the substance P analogue antagonist, [D-Arg1,D-Pro2,D-Trp7-9,Leu11]-substance P (SPA), the non-cholinergic EJPs were reduced by 60-90%; transmural stimulation now revealed an apamin-resistant IJP followed by a slow depolarization. The atropine-resistant EJPs are probably caused by the release of substance P (or a similar compound) and are likely to underlie the non-cholinergic contractions reported to occur in this tissue.     

Further evidence that substance P partly mediates the action of cholecystokinin octapeptide (CCK-8) on the guinea pig ileum but not gall bladder: studies with a substance P antagonist

The substance P antagonist, [D-Pro4-D- Trp7 ,9,10]substance P4-11, caused a pig parallel shift to the right of the cholecystokinin (CCK-8) dose-response curve in guinea pig ileum longitudinal muscle without changing the maximal contraction. The shift of the CCK-8 dose response was markedly reduced after desensitization of the tissues to substance P (SP). The SP antagonist had no effect upon CCK-8 responses of the guinea pig gall bladder, [125I]CCK pancreatic binding or contractions of the guinea pig ileum produced by acetylcholine or electrical stimulation. The data provide additional evidence for the involvement of SP in the action of CCK-8 on the guinea pig ileum but not the gall bladder.