Effect of regulatory polypeptides on the substance P stimulated lower esophageal sphincter pressure in pigs

Localization of substance P (SP)-immunoreactivity in the myenteric plexus of the rat esophagus

The present immunohistochemical study was performed to examine the number, distribution, and chemical coding of intrinsic substance P (SP) neurons and nerve fibers within the esophagus and discuss their functional roles. Many SP neurons and nerve fibers were found in the myenteric plexus, and the SP neurons gradually decreased from the oral side toward the aboral side of the esophagus. Double-immunolabeling showed that most SP neurons were cholinergic (positive for choline acetyltransferase), and few were nitrergic (positive for nitric oxide synthase). Some cholinergic SP nerve terminals surrounded cell bodies of several myenteric neurons. In the muscularis mucosa and lower esophageal sphincter, and around blood vessels, numerous SP nerve endings were present, and many of them were cholinergic. Also, SP nerve endings were found on only a few motor endplates of the striated muscles, and most of them were calcitonin gene-related peptide (CGRP)-positive. Retrograde tracing using Fast Blue (FB) showed that numerous sensory neurons in the dorsal root ganglia (DRGs) and nodose ganglion (NG) projected to the esophagus, and most FB-labeled SP neurons were CGRP-positive. These results suggest that the intrinsic SP neurons in the rat esophagus may play roles as, at least, motor neurons, interneurons, and vasomotor neurons, which are involved in local regulation of smooth muscle motility, neuronal transmission, and blood circulation, respectively. Moreover, SP nerve endings on only a minority of motor endplates may be extrinsic, derived from DRGs or NG, and possibly detect chemical circumstances within motor endplates to modulate esophageal motility.

Nitrinergic and peptidergic innervation of the human oesophagus

The distribution, colocalisation, and interconnections of nitrinergic and peptidergic neurons and nerves in the human oesophagus were examined. Cryosections of surgically resected tissues from eight subjects were studied with indirect immunofluorescence for the presence of 11 neuropeptides and neuron specific enolase. After immunohistochemistry, nitric oxide synthase was shown on the same sections with the beta nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemical reaction. The histochemical findings were verified immunohistochemically on other sections with an antiserum against nitric oxide synthase. Most myenteric neurons (55%) were nitrinergic. Most (96%) received terminations positive for vasoactive intestinal polypeptide (VIP), calcitonin gene related peptide (CGRP) (80%), and galanin (59%). The neuronal somata of 14% also contained VIP, while 10% had galanin. Of the NADPH-diaphorase containing fibers seen in the muscle layers, many had closely associated VIP and galanin, but only rarely CGRP and substance P. Thus, despite abundant representation of both peptidergic and nitrinergic systems in oesophageal smooth muscle, only VIP and galanin colocalised to any significant extent with the nitrinergic elements. These findings provide morphological support for the role of nitric oxide as the non-adrenergic non-cholinergic inhibitory mediator in the human oesophagus and for its possible interactive role with the peptidergic system.

Tachykinins in the canine gastroesophageal junction

Lower esophageal sphincter (LES) effects produced by the mammalian tachykinins were evaluated in anesthetized dogs. The distribution and content of substance P (SP) and neurokinin A (NKA) in the region of the canine gastroesophageal junction was also studied. SP and NKA stimulated a linear dose-dependent contraction of the LES after intra-arterial administration. Neurokinin B (NKB) failed to stimulate an increase in LES pressure (LESP). SP was characterized by an immediate but short-lived contraction followed by a period of relaxation. NKA stimulated a potent LES contraction that was slow in onset but long-lasting. On an equimolar basis, both SP and NKA were approximately 100 times more potent LES stimulants than bethanechol or phenylephrine. Pretreatment with atropine (muscarinic blockade) or tetrodotoxin (neural blockade) inhibited the effect produced by SP. NKA appeared to stimulate LES contraction independent of neural or cholinergic mechanisms. Radioimmunoassay revealed a regional variation in tachykinin content in the gastroesophageal junction. Ganglia, cell bodies, nerve fascicles, and neurites stained specifically for both SP and NKA. The variable effects, potencies, and mechanisms of action observed in this study suggest the presence of specific tachykinin receptor subtypes in the gastroesophageal junction. Both SP and NKA were found to have a broad neural distribution in this region. These findings suggest that the tachykinins may play an important role in neuroregulation of LES smooth muscle.

Somatostatin selectively inhibits excitatory contractile pathways of the feline lower esophageal sphincter

Intrinsic reflexes of the feline lower esophageal sphincter (LES) have been shown to be mediated by specific arrangements of excitatory peptidergic interneurons. Inhibition of intrinsic reflexes may also be mediated by neuropeptides. The specific aims of this study were: (1) to examine the effect of somatostatin (SOM) and vasoactive intestinal peptide (VIP) on basal LES tone, and (2) to determine if these transmitters exert selective inhibitory effects on excitatory contractile pathways. Intraluminal pressures were recorded from the LES, esophagus and fundus by a fixed perfused catheter assembly in anesthetized cats. Peptides were administered via the left gastric artery. SOM had no effect on basal LES pressure with doses ranging from 10(-9) to 10(-5) g/kg. VIP induced a dose-dependent inhibition of basal LES pressure. The maximal effective dose of VIP, 10(-6) g/kg, completely inhibited basal LES pressure (34.7 +/- 6.8 to 1.0 +/- 0.6 mmHg, P less than 0.001). We have previously shown that bombesin (BN) but not substance P (SP) or bethanechol contracts the LES via tetrodotoxin-sensitive pathways. BN at the D50 (5.10(-8) g/kg) increased LES pressure by 32.1 +/- 3.6 mmHg. SOM (10(-5) g/kg) decreased this BN response to 19.2 +/- 5.0 mmHg, P less than 0.05. In contrast, while the D50 of SP (5.10(-8) g/kg) gave a similar increase in LES pressure, 28.8 +/- 5.1 mmHg, this effect was not altered by SOM (23.8 +/- 6.7 mmHg, P greater than 0.10). SOM also had no effect on bethanechol-induced LES contractions (P greater than 0.10). VIP (10(-6) g/kg) totally inhibited the LES response to the D50 of BN, SP, and bethanechol. A submaximal dose of VIP (10(-7) g/kg) partially inhibited the contractile response of all three.

CONCLUSIONS

(1) VIP, but not SOM, inhibits basal LES tone. (2) SOM selectively inhibits BN but not SP- or bethanechol-induced LES contraction. (3) VIP inhibits BN, SP and bethanechol-induced LES contractions. These studies suggest that somatostatin can selectively inhibit excitatory interneurons at the LES.

Primary disorders of oesophageal motility

Primary motor disorders of the oesophagus have distinct manometric patterns but require full oesophageal investigation to exclude a secondary cause. Myotomy and forceful dilatation give good results in achalasia, though myotomy is superior in the long term. Indications for surgery are rare in diffuse spasm and nutcracker oesophagus. Non-cardiac chest pain may be related to reflux, diffuse spasm or nutcracker oesophagus, but correlation between motor abnormalities and symptoms is poor and psychological disturbances are frequent.

Influence of gastrointestinal neuropeptides on the anal canal

To evaluate the possible effect of gastrointestinal neuropeptides on anal function, the effect of somatostatin, enkephalin, VIP, and substance P on anal canal pressure and electromyographic response of the external anal sphincter was studied in healthy subjects. Enkephalin and somatostatin elicited a significant decrease in anal canal pressure after a bolus injection of 1 microgram/kg body weight whereas VIP and substance P had no effect. Future studies must show whether these effects are of pharmacologic importance and if these peptides participate in the physiologic regulation of anorectal function.

Effect of bombesin and substance P on the smooth muscle of the chicken crop

The effect of bombesin and of substance P was investigated in smooth muscle strips of the chicken crop. Bombesin in picomolar concentration (0.1 x 10(-12) - 5 X 10(-12) mol/l) caused a concentration-related contraction of the muscle strips. Substance P in nanomolar concentration (0.1 x 10(-9) - 10 x 10(-9) mol/l) was effective in the same manner. Tetrodotoxin (2 x 10(-7) mol/l) did not influence the contraction responses to either bombesin or substance P. The excitatory effect of bombesin and of substance P did not follow activation of cholinergic receptors since their effect on the crop smooth muscle was not antagonized by atropine (10(-4) mol/l) or by hexamethonium (10(-4) mol/l). Strips stored for 24 hours in the Tyrode's solution at 4 degrees C without a supply of oxygen maintained their full sensitivity to bombesin and to substance P. These results are consistent with a direct action of bombesin and substance P on the crop smooth muscle.

Regulatory peptides in lower esophageal sphincter of pig and man

Smooth muscle specimens from the lower esophageal sphincter (LES) region of pig and man were analyzed for vasoactive intestinal peptides (VIP), substance P (SP), enkephalin, neuropeptide Y (NPY), gastrin/cholecystokinin (CCK), neurotensin, and somatostatin using immunocytochemistry and radioimmunoassay. VIP-, SP-, enkephalin-, and NPY-immunoreactive nerve fibers were observed in the LES of both species, whereas nerve fibers containing gastrin/CCK, neurotensin, and somatostatin could not be demonstrated. The peptide-containing nerve fibers occurred in the intramural ganglia and in the smooth muscle layers. There was a rich supply of VIP- and NPY-immunoreactive fibers, whereas the supply of SP- and enkephalin-immunoreactive nerve fibers were moderate in number in both species examined. The concentration of VIP, SP, enkephalin, and NPY was comparable in the two species. The present study shows that the pattern of peptidergic innervation of the LES is similar in pig and man. It is proposed that neuronal VIP, SP, enkephalin, and NPY may serve to modulate the motor activity of the LES and that the pig is a suitable experimental animal for the study of regulatory peptides and LES functions.

Effect of regulatory peptides on the vagally stimulated lower esophageal sphincter pressure in pigs

The effect of vasoactive intestinal polypeptide (VIP), enkephalin, neuropeptide Y, gastrin, cholecystokinin, neurotensin, somatostatin, and thyrotropin-releasing hormone on the lower esophageal sphincter pressure (LESP) was studied in anesthetized pigs. The peptides were infused into the arterial supply of the lower esophageal sphincter in graded doses during electrical stimulation of the vagal nerve (9 V, 10 Hz, 3 msec). The vagally stimulated LESP was inhibited by VIP (0-40 pmol/kg/min) and enkephalin (0-200 pmol/kg/min) in a dose-dependent manner. The other peptides had no effect on the stimulated LESP regardless of the dose tested. The results suggest that VIP and enkephalin may influence the stimulated LESP under normal conditions and that the other peptides tested did not affect the physiological regulation of the LESP. Furthermore, the vagally stimulated LESP was inhibited by atropine (250 micrograms/kg intravenously) but not by guanethidine (1 mg/kg intravenously).