Effects of substance P antagonists on the atropine-sensitive and atropine-resistant responses of guinea-pig ileum to substance P

The effects of substance P (SP) antagonists on the atropine-sensitive and atropine-resistant responses to SP of guinea-pig isolated ileum were investigated. The atropine-resistant response to SP was the contractile response on untreated preparations, and the atropine-sensitive response was the response to high concentrations of SP (5 X 10(-7) M) on preparations desensitized to SP with a concentration of SP of 3 X 10(-7) M. The SP antagonists tested, (D-Pro2,D-Phe7,D-Trp9)-SP, (D-Pro2,D-Trp7,9)-SP, (D-Arg1,D-Pro2,D-Trp7,9,Leu11)-SP and (D-Arg1,D-Trp7,9,Leu11)-SP (spantide), did not have similar orders of potency on the atropine-sensitive and atropine-resistant responses to SP, spantide being more potent than the other antagonists on the atropine-resistant response but no more potent on the atropine-sensitive response than (D-Pro2,D-Phe7,D-Trp9)-SP or (D-Arg1,D-Pro2,D-Trp7,9,Leu11)-SP. These findings are consistent with the hypothesis that neuronal receptors for SP differ from those on smooth muscle in guinea-pig ileum.     

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.     

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.     

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.     

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.     

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.     

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.     

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)     

Neuropeptide Y: Immunocytochemical localization to and effect upon feline pial arteries and veins in vitro and in situ

Plexuses of nerve fibres containing neuropeptide Y (NPY)-like immunoreactivity invest pial arteries belonging to the circle of Willis, pial arterioles, occasionally penetrating arterioles and large veins. A more sparse supply of NPY-like fibres are observed around pial veins and venules. The NPY-immunoreactive fibres are located within the adventitia or at the adventitia-media border. Only occasional fibres are present in cerebral vessels of animals in which the superior cervical ganglion has been removed one week previously. Administration of NPY resulted in strong, concentration-dependent contractions of isolated feline middle cerebral arteries whereas administration of avian pancreatic polypeptide (APP) elicited weak contractions. In chloraloseanaesthetized cats, perivascular microapplication of NPY in situ resulted in marked concentration-dependent contractions of cerebral pial arterioles (34.7±6.6%; maximum decrease in calibre with NPY. Perivascular administration of NPY resulted in the constriction of pial veins but the magnitude of the venous calibre reductions was smaller than the response of arterioles at each reductions was smaller than the response of arterioles at each concentration examined. APP did not elicit contraction of pial arterioles or veins during in situ conditions. The pharmacological and immunocytochemical results strongly indicate the existence of a novel perivascular neuronal system containing NPY, which mediates contraction of cerebral blood vessels and NPY is colocalized with NA in sympathetic nerves.     

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.     

Comparison of the effects of potassium and pH on the calibre of cerebral veins and arteries

The vasomotor responses of individual pial veins and arteries on the convexity of the cerebral cortex to perivascular microinjection of mock cerebrospinal fluid (CSF) containing various concentrations of potassium (K⁺) and of various pH (achieved by altering the bicarbonate, HCO ₃ ^– concentration) have been examined in cats anaesthetised with -chloralose.Microapplication of CSF containing 0 mM HCO ₃ ^– (pH 4.80) effected significant increases in calibre of pial veins and arteries of 9.3±2.4% and 38.2±4% respectively (mean calibre change ±SE), whereas CSF containing 22 mM HCO ₃ ^– (pH 7.45) which constricted pial arteries significantly (–18.5±2.9%) minimally altered venous calibre (–4.3 ±2.2%).Microapplication of CSF containing 0 mM potassium resulted in a significant reduction in pial arterial calibre (–11.4±2.8%) but failed to alter pial venous calibre (–0.3 ±0.6%). Perivascular microapplication of CSF containing moderately elevated potassium concentrations (10 mM) which effected marked, significant increases in pial arterial calibre (49.3±3.9%) did not significantly alter the calibre of the pial veins (mean response –1.6±2.4%). The perivascular administration of CSF containing a high concentration of potassium (40 mM) resulted in the significant constriction of both pial veins (–13.5±0.9%) and pial arteries (–47.2±6.3%). The magnitude of the response was significantly smaller in the pial veins.The relative insensitivity to K⁺ and pH of the pial veins as compared to pial arteries suggests that alteration in the chemical composition of the perivascular fluid are of lesser importance in the control of cerebrovascular capacitance than for the regulation of cerebrovascular resistance.     

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.     

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.     

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.     

Relaxant responses to transmural stimulation and nicotine of dog and monkey cerebral arteries

In helical strips of dog and monkey cerebral arteries contracted with prostaglandin F2 alpha, transmural stimulation and nicotine produced relaxations that were abolished by tetrodotoxin and hexamethonium, respectively. These responses were attenuated by quinidine, whereas relaxations of dog coronary arteries to transmural stimulation and isoproterenol were unaffected. Treatment with vasoactive intestinal polypeptide (VIP) and substance P (SP) abolished the relaxant response of cerebral arteries to repeated applications of VIP and SP, respectively; however, after VIP or SP, a normal relaxant response to transmural stimulation or nicotine was produced. Aminophylline suppressed relaxations induced by ATP but not by nerve stimulation. VIP, SP, and adenosine 5'-triphosphate (ATP) relaxed dog cerebral arteries; the responses were unaffected by quinidine. However, only VIP and ATP relaxed monkey cerebral arteries, and SP contracted the arteries. Acetylcholine contracted monkey arteries, in which transmural stimulation produced a relaxation. It may be concluded that nerves innervating the cerebrospinal wall are stimulated electrically and chemically by nicotine, resulting in the arterial relaxation. However, a vasodilator transmitter was not identified. Quinidine appears to selectively antagonize the action of the transmitters on cerebroarterial smooth muscle.     

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.     

Dual capsaicin effects on ureteric motility: low dose inhibition mediated by calcitonin gene-related peptide and high dose stimulation by tachykinins?

The effects of capsaicin, in relation to substance P (SP), neurokinin A (NKA), neuropeptide K (NPK) and calcitonin gene-related peptide (CGRP) which coexist in local sensory nerves, on the motility of the guinea-pig ureter were studied in vivo and in vitro. Capsaicin in a low dose (10 nmol kg-1) given i.v. inhibited spontaneous, peristaltic contractions, as revealed by perfusion-pressure changes of the constantly perfused ureter in vivo. This action was independent of autonomic reflexes and prostaglandin formation. Capsaicin stimulated ureteric motility at higher doses (100 and 500 nmol kg-1). The dual effects of capsaicin on the ureteric contractility were absent 2 weeks after systemic capsaicin treatment, which depletes sensory neuropeptides. Both NKA and NPK initiated, as well as increased, the magnitude of the peristaltic contractions of the ureter, while SP only caused a minor excitatory effect. The CGRP inhibited spontaneous, as well as NKA- and NPK-induced ureteric peristaltic contractions. In vitro experiments on the ureter revealed that capsaicin (10(-6) M) induced phasic circular muscle contractions in 60% of the experiments. Neurokinin A, NPK and SP consistently increased the contractile activity. The NKA tachyphylaxis inhibited the contractile response to other tachykinins and capsaicin. The SP analogue Spantide (/D-Arg1, D-Trp7,9, Leu11/-SP) inhibited the contractile responses to SP, NKA and NPK. The CGRP also inhibited the NKA- and NPK-induced contractions of the ureter in vitro. In conclusion, capsaicin, which induces the release of mediators from sensory nerves within the ureter, has either stimulatory or inhibitory effects on ureteric smooth muscle, depending on the in vivo dose administered. The inhibitory response at a low capsaicin dose is similar to the effect of CGRP, while the contractile effects at higher doses resemble the response to tachykinins.     

Capsaicin prevents the adrenocorticotropin-induced improvement of cardiovascular function and survival in hemorrhage-shocked rats.

A volume-controlled hemorrhagic shock was produced in anesthetized rats by intermittent bleeding from an iliac vein over a period of 20-30 min, until the carotid mean arterial pressure (MAP) stabilized around 20-24 mmHg. In this condition, which caused the death of all saline-treated animals within 25-30 min, the intravenous (i.v.) bolus injection of the adrenocorticotropin fragment 1-24 (ACTH(1-24)) at a dose of 160 micrograms/kg promptly restored MAP, as well as pulse pressure, heart rate and respiratory function, and greatly prolonged the survival time. Capsaicin (125 mg/kg cumulatively, s.c., 1 week before) completely prevented the anti-shock effect of ACTH(1-24), which, on the other hand, was shared by i.v. [Nle11]-substance P (SP) (200-300 micrograms/kg). Finally the SP-antagonist [D-Arg1,D-Pro2,D-Trp7,9,Leu11]-SP prevented the effect of ACTH(1-24). These results suggest that SP-containing nerve fibers are required for the effect of ACTH in hemorrhagic shock.     

Inhibition of antidromically induced stimulation of gastric motility by substance P receptor blockade

Electrical stimulation of the feline vagal or splanchnic nerves after hexamethonium blockade of nicotinic ganglionic transmission produces gastric contractions, suggesting antidromic activation of thin afferents. The present experiments were performed to examine whether substance P is involved as a transmitter in such gastric responses. Cats were anesthetized with chloralose, laparotomized and the adrenals were ligated. The left greater splanchnic nerve, proximal to the celiac ganglion, and the left or right cervical vagal nerve were dissected, cut and placed on electrodes for peripheral stimulation. Gastric motility was monitored with a balloon. Hexamethonium was administered i.v. as well as i.a. to the stomach. Nerve stimulations produced powerful gastric contractions, which were antagonized by large doses (approximately 0.8 mumol) of substance P administered i.a. to the stomach. Similarly, the gastric contractions elicited by vagal or splanchnic nerve stimulations were reduced to at least 60% of control by the specific substance P antagonist (D-Pro2, D-Trp7,9)-SP administered i.a. (0.4-1.3 mumol). The present results support the concept that substance P is associated with gastric excitatory motor responses, possibly elicited by antidromic activation of thin afferent nerve fibres.     

Contributions of arachidonic acid derivatives and substance P to the sensitization of cutaneous nociceptors.

1. The role of presumed chemical mediators of inflammation in the heat-induced sensitization of cutaneous C-polymodal nociceptors (CPNs) was examined in a rabbit ear preparation maintained in vitro by intra-arterial perfusion with a solution free of protein and cellular elements. 2. In this preparation, CPNs consistently showed enhanced responsiveness after repeated exposure of their receptive fields to noxious levels of heat. The average magnitude of sensitization was quantitatively similar to that observed in vivo, suggesting that blood-born factors are not essential for development of sensitization. 3. Sensitization in one-half of randomly selected CPNs was blocked or reduced when the perfusate contained a cyclooxygenase inhibitor, indomethacin or dipyrone, or the dual cyclooxygenase/lipoxygenase inhibitor, BW755C, even though initial responsiveness to heat and pressure was unaltered. These observations suggest that arachidonic acid breakdown products, possibly prostaglandins, are intermediaries in the sensitization of some, but not all, C-fiber nociceptors of the skin. In addition, heat-induced sensitization for some C-fiber cutaneous nociceptors is the result of processes that are at least partially independent of those involved in excitation. 4. Substance P (SP) or the putative SP antagonists, [D-Pro2, D-Trp7.9]-SP or [D-Pro2, D-Phe7, D-Trip9]-SP, produced no significant effect on heat-responsiveness or sensitization, although ongoing activity may have marginally increased over control levels after repeated heat stimulations. We conclude that SP in an in vitro preparation is not involved in the enhancement of cutaneous C-fiber nociceptor responsiveness after repeated thermal insults.