Effects of neurotensin, substance P and methionine-enkephalin on colonic motility

The influence of neurotensin, substance P and methionine-enkephalin (met-enkephaline) on proximal and distal colonic motility was studied in anesthetized cats. When administered i.v, at a dose of 14 pmol x kg-1 x min-1, neurotensin increased basal smooth muscle tone and antiperistaltic activity in the proximal colon. After higher doses of neurotensin the basal muscle tone also increased in the distal colon. Substance P at a dose of 17 pmol x kg-1 x min-1 selectively and powerfully stimulated the distal colon, thus causing a mass contraction pattern with a concomitant decrease in peristaltic amplitude. In the proximal part of the colon 17 pmol x kg -1 x min-1 of substance P exerted an inhibitory action on the peristaltic amplitude in animals with a high level of spontaneous activity. In addition, the basal muscle tone was slightly decreased. In animals with sluggish spontaneous activity, however, no effects were detected in the proximal colon. With increasing doses of substance P forceful contractions of the proximal colon were also registered. Met-enkephalin at a dose of 40 pmol x kg-1 x min-1 increased the smooth muscle basal tone with no effect on the peristaltic activity in the proximal or distal segments. The effect on basal tone was blocked by naloxone. Thus, neurotensin, substance P and met-enkephalin have distinct motor actions on the colon. At low doses neurotensin may stimulate the churning and mixing functions of the proximal colon. Substance P exerts its major effects on the distal part with a mass contraction response and met-enkepahlin increases the basal muscle tone equally in the proximal and distal parts of the colon.     

Nervous control of the release of neurotensin-like immunoreactivity from the small intestine of the rat

Intraduodenal administration of oleic acid increased plasma neurotensin-like immunoreactivity (p-NTLI). The integrated responses to saline and oleic acid were 5.7 and 9.7 nM0-180 min, respectively. The integrated response was not significantly altered by i.v. administration of atropine, guanethidine, mepyramine, cimetidine, methysergide or a substance P antagonist, but it was abolished by hexamethonium and morphine (5.9 and 6.3 nM0-180 min, respectively). An exogenous supply of bile and pancreatic juice did not alter the integrated response in morphine- and hexamethonium-treated rats. Haloperidol significantly increased the p-NTLI response to oleic acid (13 nM0-180 min). The results suggest that the release of neurotensin is influenced by nervous pathways involving nicotinic and opioid receptors. Catecholamines and 5-HT receptors may exert an inhibitory influence on the release of NTLI.     

Mechanisms involved in colonic vasoconstriction and inhibition of motility induced by neuropeptide Y

Neuropeptide Y (NPY) and noradrenaline are suggested to coexist as neurotransmitters in sympathetic neurons. The present study investigated the mechanisms involved in the colonic vasoconstriction and inhibition of motility induced by infusion of NPY and noradrenaline close i.a. Colonic blood flow was monitored using a drop recorder, and motility was registered by a volume recording device, both operating an ordinate writer. Colonic motility was stimulated either by electrical stimulation of the pelvic nerves (PNS; 4 Hz, 5 ms, 8 V) acting via enteric ganglia or by i.v. infusion of bethanechol (10 nmol kg-1 min-1) acting directly on muscarinic receptors on smooth muscle. With both types of motility stimulation, an immediate colonic vasodilatation was registered. Electrical stimulation of the lumbar colonic nerves (4 Hz, 5 ms, 8 V) induced colonic smooth muscle relaxation and vasoconstriction during continuous PNS (P less than 0.05). Colonic contraction induced by PNS (P less than 0.01) was dose-dependently reduced by NPY (50-400 pmol min-1; P less than 0.05-0.01) and noradrenaline (1000-6000 pmol min-1; P less than 0.05-0.01). Simultaneously, vasoconstriction was induced by both NPY and noradrenaline (P less than 0.01). Colonic contraction induced by infusion of bethanechol (P less than 0.01) was not inhibited by NPY (50-200 pmol min-1). However, at the highest dose (400 pmol min-1) the motility response was reduced (P less than 0.05). Similarly, noradrenaline only at the highest dose (6000 pmol min-1) reduced the contractile response (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Distribution of neuropeptides in the limbic system of the rat: the hippocampus

The distribution of several neuropeptides (vasoactive intestinal polypeptide, cholecystokinin octapeptide, substance P, neurotensin, methionine-enkephalin and somatostatin) in the hippocampal formation has been studied with immunocytochemical techniques. Numerous vasoactive intestinal polypeptide, cholecystokinin-octapeptide and somatostatin-positive cell bodies were found within the hippocampus and subiculum. Neurotensin-positive cell bodies were found within the subiculum, but no substance P or methionine-enkephalin-containing cell bodies were seen in either hippocampus proper or subiculum. Vasoactive intestinal polypeptide and cholecystokinin-octapeptide-positive cell bodies were predominantly located in the stratum moleculare and stratum radiatum of CA 1-2 regions and dentate gyrus, whilst somatostatin-containing cell bodies were found mainly in the stratum oriens. Nerve fibres containing each of the six peptides were found within the hippocampus. Large numbers of vasoactive intestinal polypeptide, cholecystokinin-octapeptide and somatostatin fibres innervated the pyramidal and granule cell layers, with smaller numbers in the stratum radiatum and fewer still in the stratum moleculare and stratum oriens. Other than a moderately dense neurotensin-positive fibre plexus in the dorsal subiculum, fewer neurotensin, substance P and methionine-enkephalin fibres were present. However, when present, these three peptides had a distribution restricted to a region close to the pyramidal layer in the CA 2/3 region and to the stratum moleculare of the CA 1 region. Peptide-containing fibres were identified entering or leaving the hippocampus in three ways, via (i) the fornix (all six peptides), (ii) the dorsal subiculum (neurotensin-positive fibres projecting to the cingulate cortex: somatostatin, vasoactive intestinal polypeptide, and cholecystokinin-octapeptide present in fibres running between the dorsal subiculum and occipito-parietal cortex) and (iii) the ventral subiculum (vasoactive intestinal polypeptide, cholecystokinin-octapeptide and somatostatin in fibres running between entorhinal cortex and hippocampus, and all six peptides in fibres crossing the amygdalo-hippocampal border). These findings indicate a major distinction between those peptides (vasoactive intestinal polypeptide, cholecystokinin-octapeptide, somatostatin, neurotensin) which are found in cell bodies intrinsic to the hippocampal formation and those peptides (substance P, methionine-enkephalin) which are found only in hippocampal afferents.(ABSTRACT TRUNCATED AT 400 WORDS)     

Increase in neurotensin-like immunoreactivity in rat plasma after administration of calcium, bombesin and fat and its inhibition by somatostatin

Neurotensin-like immunoreactivity (NTLI) is released from the small intestine into the blood after enteral administration of fat and systemic administration of bombesin. The purpose of the present investigation in the rat was to study the effect of intravenously (i.v.) administered CaCl2 on the plasma concentration of NTLI (p-NTLI) and to investigate the effect of i.v. infusion of somatostatin on basal NTLI release, as well as that stimulated by fat, bombesin and CaCl2. Administration of CaCl2 (5-25 mg X kg-1) increased p-NTLI levels in a significant and dose-dependent manner. In contrast, somatostatin 25-200 ng X min-1) reduced the basal p-NTLI levels, as well as the increase in p-NTLI levels induced by CaCl2 (10 and 25 mg X kg-1), fat (oleic acid, 0.5 ml) and bombesin (25 and 125 pmol X kg-1), in a dose-related manner. Injection of bombesin released immunoreactive material that was indistinguishable from synthetic bovine neurotensin (1-13) upon gel-filtration. This material seemed to be rapidly converted to the more stable metabolite neurotensin (1-8).     

Central and peripheral motor effects of morphine on the rat urinary bladder

Intravesical pressure recordings were performed in anaesthetized rats, and the effect of morphine on urinary bladder function was studied. The action of morphine was registered as its influence on bladder hyperactivity induced by central catecholaminergic stimulation with 1-dihydroxyphenylalanine (L-DOPA) after peripheral decarboxylase inhibition, and as its action on the response to regional injection of receptor agonists (acetylcholine (ACh), substance P (SP)) and peripheral motor nerve stimulation (PNS). The bladder response to L-DOPA was inhibited by intracerebroventricularly (i.c.v., fourth ventricle, 10 micrograms), as well as by systemically administered (1-5 mg kg-1 i.p.), morphine. Intravenous and i.c.v. naloxone antagonised the inhibitory actions of i.v. and i.c.v. morphine, respectively. Regional intra-arterial administration of morphine (0.01-5 mg) induced a weak bladder contraction per se, with a subsequent slight depression of bladder reactivity to ACh, SP and PNS. It is suggested that the inhibitory effect of morphine on bladder motility in the rat, is mainly mediated by central opioid-receptors. The direct peripheral effects on the detrusor muscle are weak, with an initial contraction followed by slight depression of the reactivity.     

Vagotomy inhibits the effect of neurotensin on gastrointestinal transit in the rat

Neurotensin has previously been shown to delay gastric emptying, gastrointestinal transit and ileo-caecal emptying in the rat. To investigate the vagal influence on these effects of neurotensin, separate groups of rats were operated with combined vagotomy and pyloroplasty or with pyloroplasty alone and compared to a group of normal rats. All animals were supplied with a permanent gastrointestinal catheter and a venous catheter. After operation the rats were allowed to recover for 7 days, and were fasted for 24 h prior to the experiments. A radioactive marker of 1.0-0.5 ml Na2(51)CrO4 in isotonic polyethylene glycol 400 was instilled intraluminally in the stomach, proximal or distal the small intestine. Saline (control animals) or neurotensin (test animals) was given i.v. in each group studied. The animals were killed at 15, 30, 60, and 120 min after administration of the marker. The distribution of the marker in the gastrointestinal tract was registered with a scintillation detector and quantitative analysis of the amount of radioactivity retained in separate gastrointestinal segments was carried out. Gastric emptying was delayed by combined vagotomy and pyloroplasty (P less than 0.01) compared to pyloroplasty alone and normals. Neurotensin at doses of 6 (P less than 0.05) and 12 (P less than 0.01) pmol kg-1 min-1 retarded gastric emptying dose-dependently in normals and rats with pyloroplasty alone, but did not further slow the gastric emptying in rats with vagotomy and pyloroplasty. However, at a dose of 24 pmol kg-1 min-1 neurotensin delayed gastric emptying (P less than 0.01) compared to controls. Gastrointestinal transit was slowed down by neurotensin at a dose of 6 pmol kg-1 min-1 in normals (P less than 0.01) and rats with pyloroplasty alone (P less than 0.05). In rats with vagotomy and pyloroplasty, neurotensin at doses of 6 and 12 pmol kg-1 min-1 had no effect on gastrointestinal transit.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of atropine and cimetidine combinations on pentagastrin stimulated maximal gastric acid secretion in man

Recently it has been reported that anticholinergics were able to increase the inhibitory effect on gastric secretion of specific histamine H2-receptor antagonists. The aim of the present study was to determine the degree of increased inhibition of gastric acid secretion and also to introduce an exact method for measuring the gastric acid output. Maximal gastric acid secretion provoked by continuous pentagastrin infusion 3.4-4.0 micrograms X kg-1 h-1) was dose-dependently inhibited by intravenous (i.v.) atropine (0.002; 0.003; 0.004 mg X kg-1) and cimetidine (1.0; 1.5; 2.0 mg X kg-1). A potentiated synergism was observed on the simultaneous administration of atropine and cimetidine, suggesting the good effect of a low dose combination of atropine and cimetidine in the therapy of peptic ulcer.     

Possible modulatory role of dynorphin on the excitation by neurotensin on the guinea pig myenteric plexus

Dynorphin_1–13 antagonized in a concentration-dependent fashion the contractile effect of neurotensin on the isolated preparation of the guinea pig ileum myenteric plexus. The inhibitory action of dynorphin was reduced in the presence of naloxone, indicating the opioid nature of this interaction. Atropine also reduced the excitatory component of the neurotensin-induced contractile response; the joint application of atropine plus dynorphin did not cause additional inhibition of the contractile effect of neurotensin.     

Role of amines in anaphylactic contraction of guinea pig isolated smooth muscle

The possible role of acetylcholine (ACh,) histamine (His), and 5-hydroxytryptamine (5-HT) in the contractile response to ovalbumin (Oval) of ileal and tracheal muscle from sensitized guinea pigs was examined. Antagonists to these agents (atropine, mepyramine and methysergide, 5-benzyloxygramine, or 5-HT tachyphylaxis, respectively) were employed singly or in combinations. Care was always taken to ensure specificity of blockade. Results indicate that about half of the peak magnitude of the oval-induced contraction is absent in the presence of a specific inhibitory concentration of mepyramine. This finding suggests that His plays a considerable role in the oval-induced contraction. Contrary to previous reports, similar evidence was not obtained of a role for ACh and 5-HT in the Oval-induced contraction. The source of the agonists released by Oval was also investigated. Pretreatment with compound48/80 almost completely eliminated the Oval-induced contraction of ileal muscle while reducing the tracheal contraction about one-half. It would appear that the Oval-induced ileal contraction involves primarily agonists released from mast cells in the preparation whereas tracheal contraction is only partly dependent on mediators from mast cells.     

Studies on the mechanisms by which (Gln4)-neurotensin reduces lower esophageal sphincter (LES) pressure in man

The mechanisms behind the reduction of lower esophageal sphincter (LES) pressure by (Gln4)-neurotensin were investigated in 17 healthy volunteers. LES pressure was measured with a continuous pull-through technique. Intravenous infusion of (Gln4)-neurotensin (6, 12 or 18 pmol X kg-1 X min-1) caused a significant, prompt and dose-related fall in LES pressure from a mean basal value of 35.2 +/- 3.4 mmHg to 29.2 +/- 3.0, 27.3 +/- 3.5 and 25.9 +/- 2.7 mmHg, respectively. Atropine (1 mg) administered as a single i.v. bolus injection did not change the mean pressure significantly. After atropine, the LES pressure response to 12 pmol X kg-1 X min-1 of (Gln4)-neurotensin was abolished. The increase in LES pressure following a bolus injection of pentagastrin (0.6 microgram X kg-1) was not inhibited by 12 pmol X kg-1 X min-1 of (Gln4)-neurotensin. The concentration of plasma neurotensin-like immunoreactivity (p-NTLI) in all experiments was lower than, or in the same order of magnitude as, that obtained postprandially. Thus, the data indicate that reduction of LES pressure by neurotensin may occur postprandially and that this effect seems to involve a cholinergic nervous pathway, rather than being due to a direct myogenic action.     

Distribution of neuropeptides in the limbic system of the rat: the bed nucleus of the stria terminalis, septum and preoptic area

The distribution of the neuropeptides vasoactive intestinal polypeptide, cholecystokinin octapeptide, substance P, neurotensin, methionine-enkephalin and somatostatin has been mapped immunocytochemically in the bed nucleus of the stria terminalis, one of the major sites of termination for efferent projections from the amygdala. Immunoreactive fibres and terminals were distributed more or less topographically and largely in accordance with the previously described localization of peptide-containing cell bodies in the amygdala and the amygdaloid projection fields in the bed nucleus as described by neuroanatomical techniques. Thus, vasoactive intestinal polypeptide, which was found in some of the lateral amygdaloid nuclei, had a substantial projection to the lateral bed nucleus. The lateral bed nucleus also contained cholecystokinin-octapeptide, substance P, neurotensin and methionine-enkephalin immunoreactivity which probably derived from the central amygdaloid nucleus, whilst cholecystokinin-octapeptide, and especially substance P-containing fibres, were found in the medial bed nucleus and probably arise from cells in the medial amygdala. Reciprocal amygdalopetal projections were suggested by the presence of substance P- and somatostatin-containing cell bodies in the mediodorsal bed nucleus and vasoactive intestinal polypeptide cells in the lateral bed nucleus, but somatostatin otherwise had a widespread distribution. Numerous local peptidergic connections were also noted both within the bed nucleus and between it and adjacent structures, especially the preoptic area, hypothalamus and the basal ganglia. These data provide further evidence that neuropeptides play a major role in the connectivity of the limbic system and show that the bed nucleus of the stria terminalis is an important relay station, particularly between amygdaloid efferents and other forebrain areas.     

Involvement of opioid and nicotinic receptors in rectal and anal reflex inhibition of urinary bladder motility in cats

The present study was performed to investigate mechanisms involved in urinary bladder relaxation during reflex activation of the pelvic nerves in the cat. Electrical stimulation of the pelvic nerves produced a contraction of the urinary bladder (P less than 0.05) and colon (P less than 0.05). Reflex activation of the pelvic nerves by rectal distension or mechanical stimulation of the anus induced relaxation of the bladder (P less than 0.05), while a colonic contraction was elicited (P less than 0.05). Naloxone (1.5 mg kg-1, i.v.) abolished the reflex inhibition of bladder motility elicited by rectal distension or mechanical stimulation of the anus (P less than 0.05). However, the urinary bladder and colonic contraction produced by electrical stimulation of the pelvic nerves were not affected. Hexamethonium (10 mg kg-1, i.v.) or severing of the pelvic nerves completely abolished the responses of the urinary bladder and colon to electrical stimulation or reflex activation of the pelvic nerves. The results indicate that inhibitory reflexes from the rectum and anal canal to the urinary bladder are conveyed via efferents of the pelvic nerves, and involve both nicotinic and opioid receptor mechanisms.     

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.     

Direct and indirect effects of histamine on the smooth muscle cells of the guinea-pig main pulmonary artery

Electrophysiological studies of the effects of histamine on the smooth muscles in the guinea-pig main pulmonary artery revealed that this amine produced muscle contraction with an associated depolarization of the membrane. Application of cimetidine potentiated and that of mepyramine suppressed these histamine-induced responses. In the presence of mepyramine, histamine produced membrane hyperpolarization. Contractions produced by perivascular nerve stimulation were potentiated by histamine, and additional application of cimetidine further potentiated while addition of mepyramine suppressed the histamine-induced enhancement. The amplitude of excitatory junction potentials was increased by application of histamine plus cimetidine and was decreased by histamine plus mepyramine. Excitatory effects of histamine on the electrical and mechanical responses were reduced by application of tetrodotoxin, prazosin, phentolamine or guanethidine. In the presence of these drugs, histamine produced depolarization with an associated increase in membrane resistance and, in high concentrations, produced spike potentials. Electrical and mechanical responses of the smooth muscles to exogenously applied noradrenaline were potentiated by pretreatment with histamine and cimetidine, and were suppressed by histamine and mepyramine. These observations indicate that the guinesa-pig main pulmonary artery possesses two types of histamine receptor, H₁- and H₂-receptors, in the smooth muscles and in the perivascular adrenergic nerves. Stimulation of H₁ or H₂-receptor produces excitatory or inhibitory effects, respectively, on the smooth muscles and on the adrenergic nerves. Contraction of the muscle tissues produced by histamine is brought about by a direct effect on the smooth muscles and by increased release of transmitters, as a result of excitation of perivascular nerves.     

Relaxation of canine saphenous vein following brief transmural nerve stimulation

The ability of electrical stimulation to cause relaxation in the canine saphenous vein was evaluated. Rings of vein were studied isometrically in organ chambers containing physiological salt solution. Prostaglandin F2 alpha produced stable contractions, during which brief periods of electrical stimulation caused further contraction. With cessation of the electrical stimulation, tension transiently decreased to a level below that observed prior to the stimulation (undershoot). This poststimulation undershoot was blocked by tetrodotoxin, phentolamine, ouabain, and potassium-free solution; it was not affected by atropine, cimetidine, indomethacin, ketanserin, methysergide, propranolol, pyrilamine, or removal of the endothelium. Undershoot did not occur following electrical stimulation during contractions evoked by norepinephrine. During superfusion with PGF2 alpha, a brief exposure to exogenous norepinephrine caused a transient contraction followed by a subsequent undershoot. These results suggest that 1) the interaction of norepinephrine with postjunctional alpha-adrenoceptors on vascular smooth muscle leads to an increase in the activity of Na+-K+-ATPase, and 2) increased activity of Na+-K+-ATPase is responsible for the poststimulation undershoot.     

Effects of adenosine and two stable adenosine analogues on blood pressure, heart rate and colonic temperature in the rat

Adenosine exerts effects via receptors of the AI- and A2-subtype. L-phenylisopropyl adenosine (L-PIA) is more potent than N-5'-ethylcarboxamido adenosine (NECA) at the A1-subtype receptor whereas the potency order is reversed at the A2-subtype receptor. Adenosine analogues have been shown to decrease blood pressure and heart rate and to induce a marked hypothermia. In the present series of experiments adenosine, L-PIA and NECA were given i.p. or i.v. to rats, and blood pressure, ECG and colonic temperature were recorded. The NECA was the most potent of the compounds in reducing blood pressure (EC50 2 micrograms kg-1 i.v.), followed by L-PIA (EC50 approximately 30 micrograms kg-1 i.v.) and adenosine (EC50 approximately 300 micrograms kg-1 i.v.). In contrast, L-PIA and NECA were equally active in reducing heart rate (EC50 approximately 6 micrograms kg-1 i.v.). and considerably more potent than adenosine (EC50 approximately 300 micrograms kg-1 i.v.). It is suggested that simultaneous measurement of blood pressure and heart rate could be a simple in vivo model for comparison of A1- and A2-receptor subtype mediated effects. Colonic temperature was markedly reduced after i.p. administration of the adenosine analogues. Thus, 100 micrograms NECA kg-1 reduced colonic temperature from 37.8 to 26 degrees C. A 5 degrees C temperature drop was obtained by 10 micrograms kg-1 NECA, by 200 micrograms kg-1 L-PIA and by 200 mg kg-1 adenosine. The fall in colonic temperature was associated with a loss of muscular activity, as determined by needle electrodes or by palpation, indicating an inhibition of shivering.(ABSTRACT TRUNCATED AT 250 WORDS)     

Substance P and capsaicin-induced contraction of human bronchi

Substance P induced a dose-dependent contraction of human segmental bronchi in vitro with a threshold dose of about 10(-6) M. These preparations were obtained from patients undergoing lung tumor surgery. The substance P-induced contractions were resistant to mepyramine and atropine, suggesting a direct effect on the bronchial smooth muscle. Capsaicin (10(-5) M) also induced a slowly developing strong atropine-resistant contraction of human bronchi in vitro. a rapid tachyphylaxis developed for the response to capsaicin. Both substance P and capsaicin were less potent than acetylcholine and histamine in inducing contractions of human bronchi. This finding may however be partly due to the experimental conditions and both substance P and capsaicin were comparatively much more potent in guinea-pig preparations. Transmural field stimulation of the bronchial preparations in man resulted in contractions that were largely sensitive to atropine. The presence of capsaicin-induced bronchial contractions however indicates the existence of a local non-cholinergic axon-reflex control of bronchial smooth muscle tone by substance P in man.     

Effect of intrathecal capsaicin analogues on the immunofluorescence of peptides and serotonin in the dorsal horn in rats

The intrathecal administration of capsaicin, a homovanillylamide derivative, has been demonstrated to cause analgesia in response to thermal stimuli. This analgesia has been correlated with a profound depletion of spinal substance P, a putative primary afferent transmitter. We studied the effects of capsaicin, a series of capsaicin analogues, piperine and kainic acid on the immunohistochemical staining of substance P, cholecystokinin, somatostatin, methionine-enkephalin and serotonin. Capsaicin and an analogue 1-nonenoyl-vanillylamide significantly elevated the tail flick latency and when the spinal cords of the rats were analyzed immunohistochemically, a profound depletion of substance P and cholecystokinin was observed. The spinal somatostatin-immunoreactivity of these rats was slightly reduced. Piperine also depleted substance P and reduced somatostatin staining but did not alter the staining intensity or density of cholecystokinin, methionine-enkephalin or serotonin. Kainate-depleted methionine-enkephalin but did not alter any other neuropeptides studied or serotonin. These results may indicate a link between capsaicin-induced analgesia and the concomitant depletion of cholecystokinin and substance P.