F. Lembeck

Substance P as neurogenic mediator of antidromic vasodilation and neurogenic plasma extravasation.

Summary1.Antidromic vasodilation and neurogenic plasma extravasation were induced by antidromic stimulation of the saphenous nerve in guanethidine-treated rats. Vasodilation was measured by the change of outflow from the femoral vein and plasma extravasation was determined by Evans blue exudation.2.Antidromic vasodilation was reduced by 85% in adult rats which were pretreated with capsaicin on the second day of life.3.Antidromic vasodilation was inhibited by 46% after pretreatment with cimetidine plus mepyramine and by 64% after pretreatment with compound 48/80, but was not affected by pretreatment with cimetidine, atropine, methysergide, or indomethacin. Similarly, neurogenic plasma extravasation was reduced by 50% after pretreatment with cimetidine plus mepyramine, and by 88% after pretreatment with compound 48/80, but was not altered after pretreatment with indomethacin.4.Infusion of substance P into the femoral artery dose-dependently produced vasodilation (threshold: 0.1 pmol min−1) and plasma extravasation (threshold: 0.5 pmol·min−1). Vasodilation induced by substance P was inhibited by 47% after pretreatment with cimetidine plus mepyramine and by 58% after pretreatment with compound 48/80. Plasma extravasation induced by substance P was reduced by 61% after pretreatment with cimetidine plus mepyramine and by 81% after pretreatment with compound 48/80. Pretreatment with indomethacin had no influence on substance P-induced vasodilation and plasma extravasation.5.It is concluded that vasodilation and plasma extravasation following antidromic stimulation of sensory nerves are initiated by peripheral release of substance P from chemosensitive pain fibres. The actions of substance P include, besides direct effects, release of histamine from mast cells.

Decrease of substance P in primary afferent neurones and impairment of neurogenic plasma extravasation by capsaicin

1 Rats were pretreated with capsaicin (50 mg/kg, s.c.) on the 2nd, 10th, or 20th day of life. Three months later immunoreactive substance P (I‐SP) was determined in skin, sensory nerves and the central nervous system. Neurogenic plasma extravasation was also examined. 2 Pretreatment at the age of 2 or 10 days resulted in a decrease (26 to 69%) of I‐SP in skin, saphenous and vagus nerve, dorsal roots, dorsal half of the spinal cord, and medulla oblongata. The I‐SP content of the ventral half of the spinal cord, of midbrain, hypothalamus, striatum, cortex, and cerebellum remained unchanged. Neurogenic plasma extravasation was inhibited by more than 80%. 3 In contrast to this irreversible effect of capsaicin on newborn rats, pretreatment of 20 day old rats led to reversible depletion of I‐SP and to reversible impairment of neurogenic plasma extravasation. 4 Capsaicin pretreatment of adult rats caused a marked depletion of I‐SP in the skin of the hind paw and an impairment of neurogenic plasma extravasation. A similar decrease of I‐SP was seen after chronic denervation of the skin. 5 Intra‐arterial infusion of substance P (threshold dose 5 × 10−13mol/min) or physalaemin induced dose‐dependent plasma extravasation. Somatostatin, vasoactive intestinal polypeptide, caerulein and the enkephalin‐analogue FK 33–824 were ineffective in doses 100 fold higher. 6 The results indicate that the action of capsaicin on substance P neurones is restricted to primary sensory neurones. Since in every case a decreased substance P content of the skin was associated with impaired neurogenic plasma extravasation, it is suggested that release of substance P is involved in neurogenic plasma extravasation.

Vascular protein leakage in various tissues induced by substance P, capsaicin, bradykinin, serotonin, histamine and by antigen challenge

Summary1.Plasma extravasation was induced in rats or guinea-pigs by intravenous injections of (1) substance P (SP), (2) the C-terminal SP-hexapeptide SP(6-11), (3) serotonin (5-HT), (4) histamine, (5) bradykinin, (6) capsaicin and (7) by antigen challenge.2.Plasma extravasation induced by SP, SP(6-11), by 5-HT and by capsaicin was, with few exceptions, observed in the same tissues. The effect of SP was not blocked by H1 and H2 histamine receptor antagonists. The effect of i.v. capsaicin was absent in capsaicin desensitized animals. Plasma extravasation upon i.v. SP, SP(6-11), 5-HT and capsaicin was seen in the skin and in all organs containing mucous membranes except the intestinal mucosa.3.Plasma extravasation by histamine, bradykinin, and antigen challenge of sensitized guinea-pigs was, in addition, also observed in the stomach and intestine. Plasma extravasation and bronchoconstriction by antigen challenge with 20μg/kg ovalbumin was completely blocked by combined H1 and H2 histamine receptor blockade. Both responses were reduced to about the half capsaicin desensitized guinea-pigs, although the reduction of the permeability response was statistically not significant in all organs.4.In conclusion, several substances including anaphylaxis induce protein leakage in many tissues with differing selective distribution patterns. Anaphylactic histamine release leads to protein leakage partly via activation of sensory neurons. SP is a likely mediator of neurogenic protein leakage in many organs.

Substance P release from spinal cord slices by capsaicin.

Abstract The release of substance P (SP) from slices of hypothalamus, substantia nigra and spinal cord of the rat was studied. In contrast to 47 mM potassium, capsaicin induced SP release from spinal cord slices only. The SP release was not reduced by 10 −6 M tetrodotoxin but was abolished by a Ca 2+ free medium containing 3 mM ethylene-glycol-bis- (β-aminoethyl-ether) N,N-tetraacetic acid (EGTA). Capsaicin induced SP release was dose-dependent and exhibited tachyphylaxis. The ability of capsaicin to release SP supports the hypothesis that SP is involved in pain transmission and in neurogenic plasma extravasation.

Differential effects of capsaicin on the content of somatostatin, substance P, and neurotensin in the nervous system of the rat

SummaryThe distribution of immunoreactive substance P (I-SP), somatostatin (I-SRIF), and neurotensin (I-NT) and the effect of capsaicin treatment on the concentration of these peptides was studied in the peripheral and central nervous system of the rat.Neonatal capsaicin treatment (50 mg/kg s.c.) caused a depletion of I-SRIF as well as of I-SP in sensory nerves and in the dorsal half of the spinal cord. No recovery of the peptide content was found when examined 4 months later suggesting an irrerersible effect. I-NT, not a constituent of primary sensory neurons, was not changed in the spinal cord. None of the peptides studied was depleted in the hypothalamus or preoptic area.Capsaicin treatment of adult rats also led to a decrease of I-SRIF and I-SP in primarh sensory neurons. The highest dose used (950 mg/kg s.c.) induced no greater depletion than the lowest one (50 mg/kg), except for I-SP in dorsal root ganglia. Intraperitoneal injection of capsaicin led to a higher degree of depletion than subcutaneous administration as examined 1 week after treatment. In contrast to neonatal treatment, the I-SRIF content was completely restored within 4 months after treatment of adult rats. The I-SP content, however, did not completely recover in all areas but remained reduced in cornea, vagus nerve, dorsal spinal cord, and medulla oblongata for up to 9 months.Intraventricular administration of capsaicin (200 μg) caused a depletion of I-SP in the medulla oblongata but had no effect on the content of all 3 peptides in hypothalamus or preoptic area. In contrast to systemic treatment, no depletion of I-SP or I-SRIF was found in the trigeminal ganglion. Chemosensitivity of the eye was abolished after intraventricular or systemic treatment. Repeated topical application of a capsaicin solution (10 mg/ml) to the eye led within 4 h to a nearly complete depletion of I-SP in the cornea.These experiments show that capsaicin treatment of rats caused a depletion of both I-SRIF and I-SP in primary sensory neurons. While topical or systemic capsaicin administration causes depletion in terminals, the failure of intraventricular injections of capsaicin to deplete the peptides in the trigeminal ganglion suggests that depletion of the entire neuron requires an action of capsaicin on the peripheral branch and/or the cell body.

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

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

Capsaicin applied to peripheral nerve inhibits axoplasmic transport of substance P and somatostatin

Capsaicin was applied locally to the sciatic or saphenous nerve, and the effects on axoplasmic transport, neurogenic plasma extravasation, and thermal pain were studied. Capsaicin (10 mg/ml) led to a complete block of axoplasmic transport of immunoreactive substance P (I-SP) and somatostatin (I-SRIF) in rat sciatic nerve without affecting the transport of noradrenaline or acetylcholinesterase. Inhibition of I-SP transport was also found in sciatic nerves of guinea-pig, cat and rabbit. In contrast, one or two weeks after systemic capsaicin treatment (125 mg/kg s.c.), orthograde transport of I-SP was the same in control and capsaicin-treated rats. After local capsaicin application to the sciatic nerve, a decrease of I-SP was found not only in skin and sciatic nerve distal to the site of application, but also in dorsal root ganglia, dorsal roots and the dorsal half of the spinal cord segments L 4-5. This was accompanied by a loss of acid phosphatase activity in the substantia gelatinosa supplied by sciatic nerve afferents. Plasma extravasation by mustard oil was reduced in the skin of the hind paw with a time course identical to the I-SP depletion. The response to noxious heat (hot plate test) was, however, abolished earlier. These results indicate that capsaicin applied to a peripheral nerve inhibits axoplasmic transport in sensory but not in adrenergic or cholinergic neurons, which leads to long-term biochemical and functional changes of the entire sensory neuron. In addition, capsaicin appears to inhibit impulse propagation in certain populations of sensory neurons.

Effects of capsaicin on inflammation and on the substance P content of nervous tissues in rats with adjuvant arthritis

Capsaicin (20-80 mg/kg, s.c.) reduced the inflammatory response to inoculation with Mycobacterium butyricum in the rat. The effect was apparent within 24 h, was partial, persisted for well over 20 days, and occurred irrespective of whether capsaicin was administered before or after the onset of inflammation, or at the time when the pathology reached peak. Capsaicin also attenuated the increase in substance P content in sciatic nerve, saphenous nerve, dorsal root ganglia, dorsal roots, and dorsal spinal cord (L4, L5) which occurs in rats with adjuvant arthritis. The data are consistent with a possible role of substance P in the peripheral manifestations of adjuvant arthritis.

NEW, LONG-ACTING, POTENT BRADYKININ ANTAGONISTS

1 Three new bradykinin (BK) antagonists, d‐Arg0‐Hyp3‐Thi5‐d‐Tic7‐Oic8‐BK (compound I), d‐Arg0‐Hyp3‐d‐Tic7‐Oic8‐BK (compound II), and Arg(Tos)1‐Hyp3‐Thi5‐d‐Tic7‐Oic8‐BK (compound III), were tested against the effects of BK in 9 bioassay preparations including visceral smooth muscles, vasoconstriction, plasma protein extravasation, release of prostaglandin E2, bronchoconstriction, and stimulation of afferent C‐fibre nociceptors. In some of these tests the effects of the new compounds were compared with those of the antagonist d‐Arg0‐Hyp2‐Thi5,8‐d‐Phe7‐BK (compound IV), described by Stewart & Vavrek (1987). 2 For all bioassays the general rank order of potency of the compounds was found to be I > II > III ≫ IV. The new antagonists were long‐acting; in some bioassays their effects outlasted the duration of the experiment. 3 The inhibitory effects of the new BK antagonists were specific for BK; actions of noradrenaline, angiotensin II, acetylcholine or histamine were unaffected by the antagonists. They did not stimulate the release of histamine or prostaglandins. An agonistic effect was observed only with very high concentrations of compounds I and II in the plasma protein extravasation test. 4 The long duration of action of the new BK antagonists is probably due to a high and long‐lasting affinity to the BK receptors. A high resistance of the antagonists to enzymatic destruction may be another reason. 5 The new BK antagonists will be valuable tools for the investigation of the pathophysiological role of BK. In addition they may offer a potential for therapeutic applications.

Increase of substance P in primary afferent nerves during chronic pain

Abstract Substance P was found to be increased in the sciatic nerve of rats suffering chronic pain due to adjuvant-induced polyarthritis. This increase of substance P in primary afferents is assumed to reflect adaptive changes initiated by chronic noxious events such as inflammation.