S. Leander

Antagonism of the paralysis produced by botulinum toxin in the rat ☆: The effects of tetraethylammonium, guanidine and 4-aminopyridine

The injection of botulinum toxin type A into the hind-leg of adult rats causes complete paralysis of the leg lasting for several weeks. In the extensor digitorum longus (EDL) muscle transmitter release is reduced to a level of less than 1% of normal. Tetraethylammonium (TEA) and guanidine in concentrations of about 3 mM restore, in EDL muslces in vitro, neuromuscular transmission to about the normal level, provided that the external calcium concentration is 4 mM or higher. 4-Aminopyridine (4-AP) has similar restorative effect but is about 20-30 times more potent. Unlike TEA and guanidine, 4-AP is effective when the ambient calcium concentration is 2 mM; this drug is therefore also active in vivo. The intravenous injection of 4-AP (5 mg/kg body weight) restores neuromuscular transmission from complete paralysis by botulinum toxin to a normal level as shown by the recording of almost normal twitch and tetanic tensions in the EDL muscle. In rats paralysed by a lethal dose of botulinum toxin, the intraperitoneal administration of 4-AP restores general motor activity, the effect lasting 1-2 hours. A study of the effects of these drugs on spontaneous and evoked transmitter release suggests that all three compounds increase the level of free calcium inside the nerve terminals. In botulinum poisoning the transmitter release mechanism appears to be intact, but a reduced sensitivity to calcium has been shown (Cull-Candy et al. 1976), and this could explain why the drugs restore evoked transmitter release in botulinum poisoning.

Biological evaluation of substance P antagonists

1 Five undeca‐ and six C‐terminal heptapeptide substance P (SP) analogues were tested for their capacity to block the contractile effect of SP on the guinea‐pig isolated taenia coli. They had one feature in common, namely substitutions in positions 7 and 9 in the SP molecule. In the majority of analogues D‐tryptophan was used for these substitutions. 2 All analogues tested were found to be competitive antagonists to exogenous SP and to be capable of blocking the electrically induced non‐cholinergic, non‐adrenergic neuronal contraction of the taenia. 3 Of the undecapeptides, (D‐Arg1, D‐Pro2, D‐Trp7,9, Leu11) SP and (D‐Arg1, D‐Trp7,9, Leu11) SP (Spantide) had the highest pA2 value, 7.1–7.2, and the lowest IC50 value, 10−6 M. The pA2 values of the heptapeptides were generally lower. 4 Three of the most potent antagonists were tested for specificity and found to block the smooth muscle contraction induced by SP, physalaemin, eledoisin and bombesin but not that induced by bradykinin, carbachol, 5‐hydroxytryptamine, histamine, prostaglandins and vasopressin. 5 The SP antagonists were also tested for spasmogenic effect on the taenia and for their capacity to release histamine from rat isolated peritoneal mast cells. The spasmogenic activity displayed by most of the SP antagonists tested is likely to be related to their ability to release histamine since the contractile response was reduced by mepyramine, a histamine H1‐receptor antagonist. 6 (D‐Arg1, D‐Trp7, 9, Leu11) SP was notable for combining a high antagonistic potency with a weak spasmogenic effect (and poor histamine releasing effect).

Immunohistochemical localization of substance P, vasoactive intestinal polypeptide and gastrin-releasing peptide in vas deferens and seminal vesicle, and the effect of these and eight other neuropeptides on resting tension and neurally evoked contractile activity

Immunohistochemical studies of the vas deferens and seminal vesicle of mouse, guinea-pig, and rabbit showed the presence of nerve fibres containing vasoactive intestinal polypeptide (VIP), substance P (SP), and gastrin-releasing peptide (GRP) supplying the smooth muscle layers as well as blood vessels. The nerve supply was better developed in the seminal vesicle than in the vas deferens. The motor activity of the vas deferens and seminal vesicle of the guinea-pig was studied in vitro. The vas deferens responded to transmural electrical stimulation with a twitch followed by a slow contraction. The twitch was blocked by guanethidine and tetrodotoxin, but not by atropine, propranolol, phenoxybenzamine, or fluphenazine. The slow contraction exhibited features of an alpha-receptor-mediated response. SP, physalaemin and eledoisin contracted the smooth muscle and also potentiated the twitch response to electrical nerve stimulation in a concentration-dependent manner. The SP blocking agent, (D-Pro2,D-Trp7,9)-SP, affected neither the resting tension nor the response to electrical stimulation. It is therefore suggested that the SP fibres act mainly prejunctionally. VIP, Leu-enkephalin, cholecystokinin octapeptide (CCK-8), angiotensin II, vasopressin, neurotensin, bombesin, and GRP had no effect on either the resting tension or the response to electrical nerve stimulation. The seminal vesicle responded to electrical stimulation with a contraction which was unimpaired by atropine, propranolol, phenoxybenzamine, and guanethidine, but abolished by tetrodotoxin. Hence, this contraction is mediated by a non-adrenergic, non-cholinergic neurotransmitter. Bombesin, GRP, SP, physalaemin and eledoisin contracted the smooth muscle and potentiated the response to electrical stimulation. VIP, Leu-enkephalin, CCK-8, angiotensin II, vasopressin, and neurotensin had no effect on the resting tension or on the response to transmural electrical stimulation. The SP antagonist abolished the contraction elicited by SP but did not influence the response to nerve stimulation. The results suggest that the SP and GRP nerves may have prejunctional and facilitating postjunctional effects in the seminal vesicle.

THE MECHANISM OF ACTION OF A SUBSTANCE P ANTAGONIST (D‐Pro2, D‐Trp7,9)‐SP

1 A newly synthesized substance P (SP) analogue, (d‐Pro2, d‐Trp7,9)‐SP, specifically antagonizes the contractile effects of SP on the guinea‐pig isolated taenia coli. In addition, previous studies had indicated that the SP analogue per se is capable of contracting this preparation. The results of the present study on the guinea‐pig taenia suggest that the smooth muscle contractions produced by the SP analogue are due to histamine release. No contractions were observed following blockade of histamine H1‐receptors by mepyramine or following pretreatment with the histamine liberating agent, compound 48/80. 2 Analysis of the inhibition of SP‐induced contraction by the analogue suggests that the inhibition is of the competitive type; pA2 was calculated to be 6.1. 3 We conclude that (d‐Pro2, d‐Trp7,9)‐SP is a competitive SP antagonist with histamine‐releasing properties.

Nerves containing substance P, vasoactive intestinal polypeptide, enkephalin or somatostatin in the guinea-pig taenia coli

SummaryThe guinea-pig taenia coli is rich in peptide-containing nerves. Nerve fibres containing substance P (SP), vasoactive intestinal peptide (VIP), or enkephalin, were numerous in the smooth muscle while somatostatin fibres were very few. Nerve fibres displaying SP or VIP immunoreactivity were numerous in the myenteric plexus. Enkephalin nerve fibres were fairly numerous in the plexus while somatostatin nerve fibres were sparse. Nerve cell bodies containing immunoreactive SP or VIP were regularly seen in the plexus. Delicate varicose elements of the different types of nerve fibres were found to ramify around nerve cell bodies in a manner suggestive of innervation.In the electron microscope the various peptide-storing nerve fibres (i.e., elements containing SP, VIP or enkephalin) were found to contain a varying number of fairly large, electron-opaque vesicles in the varicose swellings. These vesicles represent the storage site of the neuropeptides.The isolated taenia coli responded to electrical nerve stimulation with a contraction. After cholinergic and adrenergic blockade the contractile response was replaced by a relaxation followed by a contraction upon cessation of stimulation. SP contracted the taenia while VIP caused a relaxation. The enkephalins raised the resting tension slightly while somatostatin had no effect. These observations are compatible with a role for SP as an excitatory neurotransmitter and for VIP as an inhibitory one, and with the view that both SP neurones and VIP neurones act as motor neurones. In preparations contracted by SP the electrically induced contractions were reduced in amplitude while the electrically induced relaxations seen after adrenergic and cholinergic blockade were enhanced in amplitude. In preparations relaxed by VIP there was an increased contractile response to electrical stimulation, while in the atropine + guanethidine-treated preparation the electrically induce relaxations were reduced in amplitude. The enkephalins reduced the contractile response to electrical stimulation, while somatostatin induced a very small reduction in the amplitude of such responses. These observations suggest that SP neurones and VIP neurones may play additional roles as interneurones. Somatostatin neurones probably act as interneurones. Enkephalin-containing fibres may serve to modify the release of transmitter from other nerves in the smooth muscle, perhaps through axo-axonal arrangements. Alternatively, the enkephalin nerve fibres in the smooth muscle are afferent elements involved in mediating sensory impulses to the myenteric plexus.

Neuronal cholecystokinin, gastrin-releasing peptide, neurotensin, and β-endorphin in the intestine of the guinea pig

SummaryThe guinea-pig intestine was found to harbor nerve fibers containing immunoreactive cholecystokinin (CCK), gastrin-releasing peptide (GRP), neurotensin or β- endorphin. Such fibers occurred in the myenteric and submucous ganglia and in the smooth muscle. GRP- and CCK-fibers, in addition, were found in the mucosa. Following colchicine treatment, neuronal perikarya in the myenteric ganglia displayed CCK-, GRP-, or β-endorphin immunoreactivity. CCK-immunoreactive perikarya were located also in the submucous ganglia. Neurotensin-immunoreactive cell bodies could not be detected. The presence of immunoreactive neuronal perikarya in intramural ganglia indicates that CCK-, GRP- and β-endorphin-containing fibers are intrinsic to the gut wall. GRP, neurotensin, and β-endorphin were identified in extracts of smooth muscle by immunochemical and Chromatographic analysis.CCK-8, GRP and neurotensin contracted the isolated taenia coli. Tetrodotoxin reduced the response to CCK-8 but not that to GRP and neurotensin, suggesting that the two latter peptides act directly on smooth muscle receptors. The effect of CCK-8 is partly mediated by cholinergic nerves, since not only tetrodotoxin but also atropine greatly reduced the CCK-8-induced contractile response. The substance P (SP) antagonist, (d-Pro2, d-Trp7,9)-SP1–11 had no effect on the CCK-8-induced contraction of the taenia. CCK-8 enhanced the SP-mediated (atropine-resistant) contractile response to electrical stimulation but not that mediated by acetylcholine. β-Endorphin had no effect on the tension of the muscle but reduced the response to electrical stimulation (cholinergic as well as SP-mediated) through a naloxone-sensitive mechanism.While CCK-8 and β-endorphin seem to play neuromodulatory roles in the taenia coli, the significance of GRP and neurotensin remains enigmatic.

Effects of 4-aminopyridine on mechanical activity and noradrenaline release in the rat portal vein in vitro.

4-Aminopyridine (4-AP) increased the spontaneous mechanical activity of the isolated rat portal vein. Since denervation and adrenergic receptor blockade failed to prevent this effect of 4-AP it is suggested that the drug enhances the electrical excitability of the muscle membrane. 4-AP significantly increased the response of the muscle to electrical nerve stimulation in most experiments but had little effect on the response to applied noradrenaline (NA). Both spontaneous and evoked release of 3H-activity, following preincubation in 3H-noradrenaline, were increased in the presence of 4-AP (10(-3) M). The present results with 4-AP can be explained by its known ability to block the transient potassium conductance which accompanies the action potential in excitable tissues.

Bradykinin contracts the pupillary sphincter and evokes ocular inflammation through release of neuronal substance P

Bradykinin contracts the isolated rabbit sphincter pupillae muscle. The contraction produced by 10(-8) M bradykinin was resistant to atropine but not to tetrodotoxin, suggesting a non-cholinergic nervous mechanism. The contraction was blocked by specific substance P (SP) antagonists, suggesting the involvement of SP. The SP antagonists tested were [D-Pro2,D-Trp7,9]SP-(1-11) and [Arg5,D-Trp7,9]SP-(5-11). The bradykinin-induced contraction exhibited marked tachyphylaxis in contrast to that induced by SP. It appears that the tachyphylaxis reflects the depletion of a bradykinin-sensitive neuronal pool of SP. Injection of bradykinin into the vitreous chamber of the rabbit eye caused miosis and disruption of the blood-aqueous barrier (manifested as aqueous flare). A second administration of bradykinin a few hours after the first injection evoked a reduced response; the response to SP upon repeated administration was unchanged. Atropine was without effect on the response to bradykinin whereas tetrodotoxin and the SP antagonists reduced the response. The results suggest that bradykinin causes miosis and aqueous flare at least partly through local release of neuronal SP.

Spantide II, a novel tachykinin antagonist having high potency and low histamine-releasing effect

Two undecapeptide substance P (SP) analogues, Spantide I and Spantide II, were tested for their capacity to block the contractile effect of SP on the guinea pig isolated taenia coli and the contractile effect of electrical stimulation of the rabbit isolated (and atropinized) iris sphincter, and for their capacity to mobilize histamine from rat isolated peritoneal mast cells. Spantide I and Spantide II have one feature in common, namely D-tryptophan in positions 7 and 9. Spantide I: D-Arg, Pro2, Lys3, Pro4, Gln5, Gln6, D-Trp7, Phe8, D-Trp9, Leu10, Leu11-NH2. Spantide II: D-NicLys1, Pro2, 3-Pal3, Pro4, D-Cl2Phe5, Asn6, D-Trp7, Phe8, D-Trp9, Leu10, Nle11-NH2. Both Spantide I and II were found to be competitive antagonists to SP on the taenia coli and to be capable of blocking the electrically induced non-cholinergic contraction of the iris sphincter. Spantide II had higher pA2 value (taenia coli) than Spantide I, 7.7 versus 7.0, and higher pIC50 value (blockade of tachykinin-mediated neurotransmission in iris sphincter), 6.0 versus 5.1. Both Spantide I and II mobilized histamine from rat peritoneal mast cells but Spantide II was less effective. Spantide I and II were tested for antagonistic specificity. Both blocked contractions of the taenia induced by SP and neurokinin A. In the concentration used, Spantide II in addition blocked the response to neurokinin B. The contractions induced by carbachol, 5-hydroxytryptamine, histamine and prostaglandins (F2 alpha and E1) were not affected; the contractile response to bombesin was inhibited by Spantide I but not by Spantide II.

Peptide-containing neurons intrinsic to the gut wall

SummaryNerve fibers containing substance P, VIP, enkephalin or somatostatin are numerous in the porcine gut wall. They are particularly numerous in the submucosal and myenteric plexuses where peptide-containing cell bodies are also observed. Peptide-containing nerve fibers occur also in the vagus nerves, suggesting that the gut receives an extrinsic supply of peptidergic nerves. The extrinsic contribution to the peptide-containing nerve supply of the gut wall has not yet been quantitatively assessed. In an attempt to clarify this question pigs were subjected to bilateral subdiaphragmatic vagotomy. Another group of animals was subjected to complete extrinsic denervation by autotransplantation of a jejunal segment. The pigs were killed at various time intervals after the operations; the longest time interval studied was four months. Following vagotomy the innervation pattern of the jejunum appeared completely unaffected. Following complete extrinsic denervation the adrenergic nerve fibers disappeared, while peptide-containing and acetylcholinesterase-positive nerve fibers remained apparently unaltered. This was confirmed chemically in the case of substance P.The motor activity of smooth muscle from the jejunum was studied in vitro. At low stimulation frequencies the smooth muscle from control jejunum responded by relaxation; upon cessation of stimulation a contraction occurred. With increasing stimulation frequencies the duration of the relaxation decreased; at high frequency stimulation only a contraction was recorded. In the autotransplant low frequency stimulation induced no or only a weak relaxation; high frequency stimulation induced contraction. After cholinergic and adrenergic blockade, the muscle responded with relaxation at all frequencies; the response was similar in innervated and denervated specimens. On the whole, the effects of extrinsic denervation on the motor activity of smooth muscle from porcine jejunum were minor, possibly reflecting the high degree of autonomy of the gut.