Effect of prostaglandins E1 and E2 on intestinal motility in the guinea-pig and rat

Role of PGE2 in colonic motility: PGE2 attenuates spontaneous contractions of circular smooth muscle via EP4 receptors in the rat colon

Colonic motor activity is important for the formation and propulsion of feces. The production of prostaglandins (PGs) in colonic tissue is considered to play a critical role in the generation and regulation of colonic motility. In this study, we investigated the inhibitory effects of PGE2 and selective agonists of four EP receptors on the spontaneous phasic contractions, called 'giant contractions' (GCs), of mucosa-free circular smooth muscle strips from the rat middle colon. Neural blockade with tetrodotoxin (TTX) increased the frequency and amplitude of the GCs by about twofold. However, inhibiting PG production with piroxicam reduced the GC frequency in the presence of TTX, but did not affect the GC amplitude. In the presence of both TTX and piroxicam, exogenous PGE2 and each EP receptor agonist were cumulatively added to the tissue bath. In this setting, PGE2, the EP2 agonist ONO-AE1-259, and the EP4 agonist ONO-AE1-329, but not the EP1 agonist ONO-AE-DI-004 or the EP3 agonist ONO-AE-248, concentration-dependently reduced the GC frequency and amplitude. The PGE2-induced inhibition of GC frequency and amplitude was inhibited by the EP4 antagonist ONO-AE3-208, but not by the EP1/2 antagonist AH6809. Immunohistochemistry revealed the EP2 and EP4 receptors were localized in perinuclear sites in circular smooth muscle cells. EP2 immunoreactivity was also located in GFAP-immunoreactive enteroglia, whereas EP4 immunoreactivity was also located in HU (embryonic lethal, abnormal vision [ELAV] protein; a marker of all myenteric neurons)-immunoreactive myenteric nerve cell bodies. These results suggest that the PGs produced in the colonic tissue inhibit the GC frequency and amplitude of circular muscle in the rat middle colon, and is mediated by EP4 receptors expressed in the smooth muscle cells.

Involvement of different receptor subtypes in prostaglandin E2-induced contraction and relaxation in the lower esophageal sphincter and esophageal body

Prostaglandin E₂ (PGE₂) plays a role in the pathogenesis of gastro-esophageal reflux disease (GERD). There are 4 subtypes of PGE₂, PGE₂ receptor 1, 2, 3 and 4 (EP 1-4). In GERD patents, PGE₂, EP2 and EP4 are upregulated. However, the effects of PGE2 on esophageal motility remain elusive. We examined how PGE₂ regulates motility in the porcine circular smooth muscle of the lower esophageal sphincter (LES), and the circular and longitudinal smooth muscle of the esophagus body in organ bath. PGE₂ induced tonic relaxation in the LES and circular smooth muscle, but transient contraction in longitudinal smooth muscle. The relaxation of the LES and circular smooth muscle was similar in pattern and mechanism, but was much larger in the LES. The relaxation was completely blocked by a voltage-gated K⁺ channel blocker or 40 mM K⁺ depolarization, indicating the involvement of K⁺ channel. Longitudinal smooth muscle contraction was completely blocked by an L-type Ca²⁺ channel blocker, showing the contribution of Ca²⁺ movement. The involvement of the EP receptor in motility was examined with selective receptor agonists and antagonists. Activation of EP2 and EP4 caused relaxation in the LES and circular smooth muscle. Compatible with PGE₂, EP2 and EP4 agonists caused more significant relaxation in the LES than in circular smooth muscle. EP1 contributed to the longitudinal smooth muscle contraction. The different effects of PGE₂ in the LES, circular and longitudinal smooth muscle contributes to esophageal motility, their impairment might increase the amount and frequency of esophageal reflux.

Rotavirus infection increases intestinal motility but not permeability at the onset of diarrhea

The disease mechanisms associated with onset and secondary effects of rotavirus (RV) diarrhea remain to be determined and may not be identical. In this study, we investigated whether onset of RV diarrhea is associated with increased intestinal permeability and/or motility. To study the transit time, fluorescent fluorescein isothiocyanate (FITC)-dextran was given to RV-infected adult and infant mice. Intestinal motility was also studied with an opioid receptor agonist (loperamide) and a muscarinic receptor antagonist (atropine). To investigate whether RV increases permeability at the onset of diarrhea, fluorescent 4- and 10-kDa dextran doses were given to infected and noninfected mice, and fluorescence intensity was measured subsequently in serum. RV increased transit time in infant mice. Increased motility was detected at 24 h postinfection (h p.i.) and persisted up to 72 h p.i in pups. Both loperamide and atropine decreased intestinal motility and attenuated diarrhea. Analysis of passage of fluorescent dextran from the intestine into serum indicated unaffected intestinal permeability at the onset of diarrhea (24 to 48 h p.i.). We show that RV-induced diarrhea is associated with increased intestinal motility via an activation of the myenteric nerve plexus, which in turn stimulates muscarinic receptors on intestinal smooth muscles.

IMPORTANCE

We show that RV-infected mice have increased intestinal motility at the onset of diarrhea, and that this is not associated with increased intestinal permeability. These new observations will contribute to a better understanding of the mechanisms involved in RV diarrhea.

Role of PGE2 in the colonic motility: PGE2 generates and enhances spontaneous contractions of longitudinal smooth muscle in the rat colon

The aim of this study was to determine which PGE2 receptors (EP1-4 receptors) influence colonic motility. Mucosa-free longitudinal smooth muscle strips of the rat middle colon spontaneously induced frequent phasic contractions (giant contractions, GCs) in vitro, and the GCs were almost completely abolished by a cyclooxygenase inhibitor, piroxicam, and by an EP3 receptor antagonist, ONO-AE3-240, but enhanced by tetrodotoxin (TTX). In the presence of piroxicam, exogenous PGE2, both ONO-AE-248 (EP3 agonist), and ONO-DI-004 (EP1 agonist) induced GC-like contractions, and increased the frequency and amplitude. These effects of EP receptor agonists were insensitive to TTX and ω-conotoxins. In immunohistochemistry, the EP1 and EP3 receptors were expressed in the longitudinal smooth muscle cells. These results suggest that the endogenous PGE2 spontaneously generates and enhances the frequent phasic contractions directly activating the EP1 and EP3 receptors expressed on longitudinal smooth muscle cells in the rat middle colon.

Immune mediators of postoperative ileus

CLINICAL BACKGROUND: In all patients undergoing abdominal surgery, a transient phase of interruption of bowel motility, named postoperative ileus (POI) occurs. POI is often accepted as an unavoidable "physiological" response and a self-limiting complication after surgery although it has a significant impact on patient morbidity with prolonged hospitalization and increased costs. Annual economic burden has been estimated as much as US $1.47 billion in the USA (Iyer et al. in J Manag Care Pharm 15(6):485-494, 2009).

PATHOPHYSIOLOGY

The pathophysiology has been elucidated within the last decades, demonstrating that both, neurogenic and inflammatory mechanisms are involved in response to the surgical trauma. It is now generally accepted that POI pathogenesis processes in two phases: a first neurogenic phase is accountable for the immediate postoperative impairment of bowel motility. This is followed by a second immunological phase that can last for days and mainly affects strength and length of POI. More recent findings demonstrate a bidirectional interaction between the nervous and the immune system, and this interaction significantly contributed to our present understanding of POI pathophysiology. Although nerval mechanisms have a significant impact in the early phase of POI, the contribution of the immune system and subsequently its manipulation has risen as the most promising strategy in prevention or treatment of the clinically relevant prolonged form of POI.

AIMS

The present manuscript will give an update on the inflammatory responses, the involved cell types, and participating immune mediators in POI.

The effects of PGE2 and PGF2 alpha on rhythmic contractions of sphincter of Oddi

1. Spontaneous rhythmic activity observed in some of the guinea-pig sphincter of Oddi preparations was completely abolished by PGE2 (10(-8) M) but not altered by PGF2 alpha (10(-6) M). 2. Indomethacin (10(-5) M), a cyclooxygenase inhibitor, elicited long-lasting rhythmic contractions in 50% of the preparations tested, which did not show any spontaneous activity. PGE2 (10(-8) M) completely inhibited, however PGF2 alpha (10(-8)-10(-6) M) did not change the rhythmic contractions induced by indomethacin. 3. Both initial phasic contraction and the frequency and amplitude of peristaltic waves induced by ACh (10(-3) M) were increased by indomethacin (10(-5) M), decreased by PGE2 (10(-7) M) and not altered by PGF2 alpha (10(-7) M).

Eicosanoids and the gastrointestinal tract

Determining the role of eicosanoids in gastrointestinal physiology and pathophysiology has been an active area of investigation over the past 20 years. The landmark discovery of prostaglandin endoperoxide synthase and other enzymes involved in the production of arachidonic acid products (lipoxygenases and epoxygenases) ushered in a new era of research. The goal of this review is to distill a large body of work pertaining to studies of eicosanoids in the gastrointestinal tract. This review has been organized according both to functional (secretion and motility) and disease-related (inflammation, mucosal injury, and neoplasia) effects. The aim of this article is to present a clear summary of this area of gastroenterology so that future research can be directed in a logical and productive manner.

Contractile response to neuropeptide Y of rat isolated duodenum

The response of isolated duodenum to neuropeptide Y (NPY) was studied isotonically in neonatal and adult rats. Neuropeptide Y (10(-8) to 10(-6) M) elicited a biphasic contraction of isolated duodenum from neonatal rats, but monophasic and weak contraction of adult duodenum. The first phase of NPY-induced contraction of neonatal duodenum was concentration dependent and partially inhibited by preincubation with tetrodotoxin, a Na+ channel blocker, hyoscine, a muscarinic antagonist, suramin, a P2 purinoceptor antagonist, and indomethacin, an inhibitor for prostaglandin biosynthesis. Neuropeptide Y(13-36), a specific Y2 NPY receptor agonist, elicited a concentration-dependent contraction of neonatal rat duodenum. The duodenal response to NPY thus changes during development in rats. Both cholinergic and purinergic transmission and prostaglandin biosynthesis may be involved in the NPY-induced contraction of neonatal duodenum. Neuropeptide Y-induced contraction may be mediated through presynaptic Y2 receptors.

Motor effects of indomethacin, morphine or vagal nerve stimulation on the feline small intestine in vivo

Some factors known to affect jejunal motility (recorded as volume changes of an intraluminal balloon) were investigated in anaesthetized cats (ether-chloralose) pretreated with guanethidine and atropine. Indomethacin, morphine (both compounds administered systemically) or vagal nerve stimulation elicited jejunal excitatory motor responses. The effect of indomethacin seemed to be independent of cyclooxygenase inhibition and probably did not involve opioid receptors. It is suggested that the spasmogenic stimuli caused jejunal hypermotility by inhibiting tonically active, inhibitory motor neurons that are intrinsic to the gut. Furthermore, when the jenunal tone had been raised by indomethacin or morphine spontaneous relaxations were observed, and these could be mimicked by vagal stimulation. Hexamethonium antagonized these relaxations but did not attenuate the drug-induced jejunal hypermotility.

Contractile effects of prostaglandin E2 in rat rectum: Sensitivity to the prostaglandin antagonists diphloretin phosphate and SC 19220

Prostaglandin E2 (PGE2) applied cumulatively (1 nM-1 microM) induced concentration-dependent tonic contractions in the longitudinal muscle of isolated rat rectum. The PGE2 effects were not altered by guanethidine (50 microM), whereas atropine (3 microM), guanethidine plus atropine or tetrodotoxin (0.1 microM) reduced them to an almost equal extent and increased the EC50 values for PGE2. The after-contractions following electrical stimulation were enhanced by PGE2 (10 nM) and inhibited by atropine. Diphloretin phosphate (DPP, 100 microM) shifted the regression lines for PGE2 to the right in both untreated and tetrodotoxin-treated preparations, and thereby increased the EC50 values. Slopes of the concentration-effect lines for PGE2 before and after DPP differed in the presence of tetrodotoxin. The regression line for PGE2 with SC 19220 (100 microM) in tetrodotoxin-treated preparations was shifted to the right in a parallel fashion. It is concluded that PGE2 exerted both a neural (cholinergic) and a smooth muscle effect. There may be a competitive antagonism between SC 19220 and PGE2 but the block by DPP may be nonselective.

Gastrointestinal food hypersensitivity: basic mechanisms of pathophysiology

Gastrointestinal symptoms occur in a large number of patients with food allergies. Immediate hypersensitivity mechanisms may give rise to the nausea, vomiting, abdominal pain, and diarrhea experienced by these patients. However, there are limited human data about the pathophysiological basis for these symptoms. Most of the available information comes from a variety of animal models. This article reviews the literature using models of intestinal food hypersensitivity, as well as human studies, that have contributed to our understanding of the pathophysiological mechanisms in gastrointestinal food hypersensitivity.

A comparison in vitro of human and rabbit distal colonic muscle responses to inflammatory mediators

The present study compared in vitro the motor responses of human and rabbit distal colonic longitudinal and circular muscle to acetylcholine, histamine, leukotrienes B4 and D4, and prostaglandins E2 and F2 alpha. The active and passive mechanical properties of these muscles were also evaluated. All muscle types were contracted by acetylcholine and histamine. Longitudinal muscle from both species was contracted by prostaglandin E2 and prostaglandin F2 alpha, although rabbit muscle was more sensitive. Prostaglandin E2 relaxed the majority of both human and rabbit circular muscle preparations that were studied. Prostaglandin F2 alpha first relaxed and then contracted circular muscle from both species. Leukotriene B4 had no effect on any tissue studied. Leukotriene D4 caused transient relaxations in a proportion of all muscle types, but the relaxations were not concentration-related. Contractile responses did not differ under isotonic recording conditions, but relaxations were much more clearly defined. Based on experiments using atropine, phentolamine and propranolol, and pyrilamine or tetrodotoxin, it was concluded that the responses of both human and rabbit distal colonic muscles to these inflammatory mediators have a similar pharmacological basis. All muscle types exhibited low passive tension and developed active tension in the range 0.8-1.2 Lo. These data strongly support the belief that after the onset of an induced colitis, the rabbit colon has value as a predictive model for the study of inflammatory mediator-induced colonic motility changes in humans.

Postnatal changes in response to adenosine and adenine nucleotides in rat duodenum

1. The effects of adenosine and adenine nucleotides were studied in rat duodenum from postnatal day 1 to day 70. The mechanical activity of duodenal segments was recorded through an isotonic transducer connected to a polygraphic recorder. 2. In rat duodenal segments, adenosine-5'-triphosphate (ATP, 10(-4) M) and adenosine-5'-diphosphate (ADP, 10(-4) M) produced a contractile response on postnatal day 1. This response increased with age, peaking on day 7, followed by a gradual decrease and was non-existent by day 21. In contrast, a relaxant response to ATP and ADP was apparent on day 21, and continued to increase up to day 70. 3. The contraction caused by ATP was inhibited by indomethacin or the P2y-purinoceptor antagonist, reactive blue-2 but not by tetrodotoxin or hyoscine. Thus, it may be mediated by production of prostaglandin through the P2y-purinoceptor. The relaxation produced by ATP was inhibited by reactive blue-2 but not by tetrodotoxin, guanethidine or the P1-purinoceptor antagonist, 8-phenyltheophylline indicating that ATP acts on smooth muscle directly through the P2y-purinoceptor. The pD2 for the contractile response to ATP was 5.15 on day 7 and that for the relaxant response, 6.64 on day 70. 4. Adenosine (10(-4) M) and adenosine-5'-monophosphate (AMP, 10(-4) M) elicited no response before day 14. On day 14, both adenosine and AMP produced a small relaxant response which increased with age. The relaxation produced by adenosine was inhibited by 8-phenyltheophylline but not by tetrodotoxin or guanethidine, indicating that it is mediated by an action on the P1-purinoceptor of smooth muscle. 5. It is evident from these results that in neonatal rat, a contractile response to ATP and ADP occurs initially in the duodenum, followed by a relaxant response to adenosine and AMP on day 14 and to ADP and ATP on day 21. 6. The smooth muscle of rat duodenum may tentatively be concluded to contain separate purinoceptors for adenosine and AMP (Pj) and ADP and ATP (P2) and the responses to P1- and P2-agonists change during the course of development.

Prostaglandin E2 induced the cyclic AMP-dependent release of acetylcholine in circular muscles of the isolated guinea pig ileum

Prostaglandin E2 (PGE2) induced a dose-dependent increase in tone of the circular muscles of guinea pig ileum in vitro. These actions of PGE2 were deleted in the cold-stored preparations and blocked by tetrodotoxin. Atropine reduced the effects of PGE2 and physostigmine potentiated the PGE2-induced contractions. The release of acetylcholine (ACh) by PGE2 was responsible for initiating this contraction. The effect of PGE2 was compared with that of an electrical stimulation which also initiated a non-receptor-mediated release of ACh. Hexamethonium abolished the effect of PGE2 but did not influence the actions of the electrical stimulations. Synaptosomal fractions of the circular muscles were prepared to study the release of [14C]ACh. However, PGE2 failed to evoke a marked increase in the efflux of radioactivity, even at the maximal concentration. Damage and/or removal of the myenteric plexus may be responsible for this result because electrical stimulations that exert a powerful spasmogenic effect on longitudinal muscles also induced an insensitive response. Alloxan and ethacrynic acid, inhibitors of adenylate cyclase, reduced the activity of PGE2 at a concentration insufficient to modify either the actions of ACh or the electrical stimulations. 3-Isobutyl-1-methylxanthine (IBMX) potentiated the responses to PGE2 at a dose sufficient to block the activity of phosphodiesterase (PDE). Imidazole, a stimulator of PDE, decreased the actions of PGE2 in a dose-dependent manner. IBMX, like imidazole, failed to modify the activities of both ACh and the electrical stimulations. These results indicate that PGE2 may function as a releaser of ACh in a cyclic AMP-dependent manner in the circular muscles of guinea pig ileum.

Synthesis and biological properties of 16(S)-amino-PGF2 alpha methyl ester

A synthesis of 16-amino-derivatives of PGF2 alpha is reported. Introduction of an amino group into position 16 of PGF2 alpha has decreased the sensitivity of the compound to metabolic degradation. 16(S)-amino-PGF2 alpha methyl ester shows high abortifacient activity with reduced diarrhoeic side effect.

The effects of PGF2 alpha, PGE2 and 16, 16 dimethyl PGE2 on gastric emptying and small intestinal transit in rat

Prostaglandins are well known for their ability to stimulate contraction in gastrointestinal smooth muscle, yet very little information is available on how their activity affects propulsion in vivo. Thus, studies were undertaken to determine the effect of various prostaglandins on gastric emptying (GE) and small intestinal transit (SIT) in unanesthetized fasted rats. Rats were treated with intravenous, subcutaneous, or oral PGF2 alpha, PGE2, or 16, 16 dimethyl PGE2 at various doses, followed 1 (intravenous), 20 (subcutaneous) or 10 (oral) mins later by intragastric 51Cr oxide in black ink. Forty-five mins later, rats were sacrificed by CO2 asphyxiation, the pylorus clamped, and the gut excised. SIT was expressed as the percent of intestinal length traveled by the most distal portion of ink. GE was expressed as the percent of the 51Cr emptied into the intestines. If GE was affected by prostaglandin treatment, the experiments were repeated with rats pre-implanted with duodenal cannula. This preparation allowed the visual transit marker to be deposited directly into the duodenum, thus avoiding acceleration or delay of SIT caused by fluctuations in GE. The results of these studies show that: (1) intravenous 16, 16 dimethyl PGE2 (5-50 micrograms/kg), but not PGF2 alpha or PGE2, accelerates GE and delays SIT; (2) oral prostaglandin administration increases SIT; (3) oral 16, 16 dimethyl PGE2 delays GE; (4) subcutaneous 16, 16 dimethyl PGE2 accelerates, has no effect upon, or delays GE depending upon dose, but accelerates SIT at all doses tested; and (5) subcutaneous PGE2 accelerates SIT while PGF2 alpha does not. Thus, the effect of prostaglandins on GE and SIT depends upon the dosage and route of administration as well as type of prostaglandin used.

Influence of prostaglandins on bovine abomasum: biosynthesis and in vitro motility experiments

Pieces of the fundus, antrum pyloricum and pyloric sphincter of abomasa from freshly killed cows were studied for their capacity to biotransform arachidonic acid (AA) and for the effects of PG's on their in vitro motility. Biotransformation experiments revealed an AA-conversion (3.8 to 11.5%) into cyclooxygenase and lipoxygenase metabolites. The mucosa mainly synthetized hydroxy-eicosatetraenoic acids (HETE's) and PGE2 + TXB2. For the muscularis PGI2 was the major AA-metabolite. Incubation in the presence of indomethacin resulted in a reduction of the AA-conversion into cyclooxygenase metabolites. In the fundic strips the three PG's induced an increase in tension. In the antral strips PGF2 alpha and PGE2 resulted in an activation of spontaneous motility whereas PGI2 provoked a dose-dependent inhibition. The three PG's induced an inhibitory response in the tissue strips from the pyloric sphincter. The results suggest a possible function for PG's in the control of tone and motility of the bovine abomasum.

The effect of leukotriene D4 on the isolated stomach and colon of the rat

The effect of synthetic leukotriene D4 (LTD4) was evaluated on isolated gastric longitudinal or circular smooth muscle and distal colon of the rat. The concentrations of LTD4, 2.5 X 10(-10)M to 5 X 10(-7)M, evoked minimal to maximal contractile responses. In addition, selected prostaglandins were used to identify the mediator of LTD4-induced contraction of gastric smooth muscle. FPL 55712 inhibited LTD4-induced contractions of gastric longitudinal or circular muscle. Indomethacin inhibited only LTD4-induced contractions of the longitudinal muscle. A combination of FPL 55712 and indomethacin produced greater inhibition of LTD4-induced contractions of longitudinal muscle than either agent alone. However, the same combination of inhibitors showed no greater effect than FPL 55712 alone on LTD4-induced contractions of circular smooth muscle. Unlike PGI2, PGF2, PGA2, or PGD2, PGE2 evoked contraction of the longitudinal muscle and relaxation of the circular muscle of the stomach. The dissimilar effect of PGE2 in the two smooth muscle layers of the rat stomach may signify that PGE2 is the prostaglandin released by LTD4 from the longitudinal and circular gastric muscle. However, the opposing pharmacologic effects following LTD4-induced release of prostaglandins in the circular muscle of the stomach would preclude the appearance of an inhibitory effect of indomethacin in this tissue. In contrast, PGE2 and other prostaglandins contract gastric longitudinal muscle in response to LTD4. Thus, these studies clearly suggest that LTD4 has both a direct and indirect effect on gastric smooth muscle of the rat. Unlike the stomach, LTD4-induced contraction of the distal colon was not inhibited by indomethacin while FPL 55712 antagonized contractions. Thus, these findings indicate a differential mechanism of stimulation of rat gastrointestinal tissue by LTD4.

Bioassays of smooth muscle contracting agents in cotton mill dust and bract extracts: arachidonic acid metabolites as possible mediators of the acute byssinotic reaction

Byssinosis is an occupational respiratory disease contracted by cotton mill workers who inhale cotton mill dust. The acute byssinotic reaction is characterized by a drop in the 1-sec forced expiratory volume (FEV1.0) on Monday following a weekend's absence from work. This physiological reaction is the result of the contraction of bronchial smooth muscle, which causes narrowing of small airways. An isolated tissue bath technique was used to assay smooth muscle contractions induced by cotton dust extract (CDE) and cotton bract extract (CBE). CBE-induced contractions of rat stomach smooth muscle were blocked (82%) by 100 ng/ml methysergide (blocks 5-hydroxytryptamine (5HT) 100%); CDE was not significantly blocked by methysergide (13%). CDE-induced contractions were blocked (100%) by 25 micrograms/ml indomethacin and 100 micrograms/ml salicylic acid (blocks prostaglandin F2 alpha (PGF2 alpha) 100%). The portion of CBE contracting ability not blocked by methysergide was blocked totally by indomethacin. Blocking agents ineffective against CDE or CBE include atropine (acetylcholine blocker), pyrilamine maleate and diphenhydramine (histamine blockers), imidazole and 7-(1-imidazolyl)heptanoic acid (7IHA) (thromboxane blockers), and carboxypeptidase B2 (kinin blocker). The data suggest that cotton bract contains 5HT, which is responsible for a majority of the CBE-induced contraction and a minority of the CDE-induced contraction. The data also suggest that cotton dust and bract contain a substance which causes the release of PGF2 alpha which in turn causes the contraction of smooth muscle. This substance is responsible for a majority of the CDE-induced and a minority of the CBE-induced contractions. Radioimmunoassay (RIA) confirmed PGF2 alpha release from rat fundal smooth muscle when exposed to CDE and CBE. Increased synthesis and release of arachidonic acid metabolites might be a major mechanism in the bronchoconstriction observed in the acute byssinotic reaction.

Contractile responses of longitudinal and circular smooth muscle of the canine stomach to prostaglandins E and F2alpha

Muscle strips were excised from the circular and longitudinal layers of the fundus, corpus and antrum, and from the inner portion of the pyloric ring. In general prostaglandin (PG)F2 alpha as well a PGE1 and PGE2 stimulated the longitudinal muscle. However, there were remarkable regional differences. The sensitivity to PGs was greatest in the fundus and corpus (threshold near 10(-10) mol/l) and only weak in antrum (threshold 5.10(-8) to 10(-7) mol/l). In longitudinal antrum strips acetylcholine induced a combined phasic-tonic response, whereas PGs produced purely phasic response. The effects of PGF2alpha and PGE on the circular layer were complex. PGF2 alpha produced excitatory responses in circular fundus and corpus similar to those in the longitudinal layer of the same regions. PGE produced dual responses in circular fundus (excitation at low concentration and strong inhibition at concentration of 10(-7) mol/l). In circular corpus PGE induced pure inhibition (threshold near 10(-9) mol/l for inner pylorus). These effects of PGs appeared in the presence of adrenergic and cholinergic blocking agent as well as of tetrodotoxin and were, therefore, direct effects on smooth muscle. Indomethacin (10(-7)-10(-6) mol/l) suppressed spontaneous tone of the fundus and corpus and increased phasic activity of inner pylorus. This indicates that endogenous PG synthesis may be involved in the control of spontaneous activity in gastric muscle.

Acetylcholine release from the myenteric plexus of guinea-pig ileum by prostaglandin E1

Release of acetylcholine (ACh) by prostaglandin E1 from the nerve terminals of the guinea-pig longitudinal muscle strip was studied in order to reveal the effect of PGE1 on myenteric plexus activity. The ACh released was collected in the presence of physostigmine (2.1 microgram ml-1) and choline (0.1 microgram ml-1) at 38 degrees C. Five to 100 ng ml-1 PGE1 enhanced the release dose-dependently. The effect was maintained during the presence of PGE1 in the organ bath, while rapid tachyphylaxis was observed with the ACh-releasing action of nicotine. Tetrodotoxin or morphine almost completely inhibited the effect of PGE1 on ACh release. Hexamethonium, in a concentration which completely blocked the effect of nicotine, partially inhibited the effect of PGE1. In the late phase of nicotine action, the tissue was still sensitive to PGE1 despite the continued exposure to nicotine. These data suggest the presence in the myenteric plexus of PG receptors which can increase ACh release.

Prostaglandins and serotonin: nonpeptide diarrheogenic hormones

Prostaglandins and serotonin are vasoactive compounds with profound effects on the gastrointestinal tract. Both cause inhibition of gastric acid secretion (although serotonin stimulates gastric pepsin secretion), stimulation of intestinal motility, and conversion of small intestinal mucosa from absorption to secretion of water and electrolytes. Their effects on pancreatic and biliary function are still not clear. Although prostaglandins appear to elicit their effects primarily by a paracrine mode of action, and serotonin is primarily a neurotransmitter (neurocrine), it is clear that even under normal conditions both can function as humoral agents. For example, we have shown that serotonin plays a physiologic role as a humoral inhibitor of gastric acid secretion. However, the effects of these agents become more pronounced in patients with humorally mediated diarrheogenic syndromes. Serotonin (and related indoles, particularly 5-hydroxytryptophan) has been firmly implicated as a cause of diarrhea in patients with carcinoid syndrome; our recent studies suggest that the diagnosis can be more effectively made by measuring circulating immunoreactive serotonin concentrations than urinary excretion of 5-HIAA; that some circulating serotonin escapes hepatic inactivation and, thus, large intestinal tumors can cause carcinoid syndrome in the absence of hepatic metastases; and that large amounts of serotonin are produced by some noncarcinoid diarrheogenic tumors, including medullary carcinomas of the thyroid and tumors associated with the WDHA syndrome. A large number of tumors of probable neural crest origin, including medullary thyroid carcinoma, carcinoids, and tumors associated with the WDHA syndrome, secrete large amounts of prostaglandins, particularly PGE2. The clinical response of at least some of the patients harboring these tumors to inhibitors of prostaglandin synthesis (particularly indomethacin) suggests that prostaglandins play a role in the etiology of these diarrheogenic syndromes.

Effect of prostaglandin E1 and indomethacin on responses of longitudinal muscle of guinea-pig ileum to cholecystokinin

The effect of prostaglandin E1 (PGE1) and indomethacin (IND) cholecystokinin (CCK)-induced contractions of guinea-pig isolated ileum longitudinal muscle were studied. PGE1 (2.8--28 nM) consistently and dose dependently increased the contractions evoked by CCK (indirect muscle stimulation) or by ACh. IND (2.7 microM) decreased the contractions to both compounds and this was reversed with 2.8--7 nM PGE1. Pretreatment of the preparations with phentolamine (2.6 microM) or pretreatment of the animals with reserpine (2 mg/kg i.p. 24 h before killing) did not affect PGE1 potentiation or IND inhibition of CCK-induced contractions. The results indicated that PGE1 potentiated CCK-induced contractions of the longitudinal muscle of guinea-pig ileum by increasing the response to released ACh. Experiments with IND suggested that endogenous PGs may modulate the effect of CCK or related gastrointestinal hormones.

The effect of PGE1 on peristalsis and on perivascular nerve inhibition of peristaltic activity in guinea-pig isolated ileum

The effect of PGE1 on peristalsis of guinea-pig isolated ileum was examined using a modified Trendelenburg method to evoke and record peristaltic activity. PGE1 (14 nM, 0.11 microM and 0.56 microM) increased peristaltic activity of both longitudinal and circular muscle, mainly by increasing the amplitude of contraction. Preparations of ileum subjected to a 'minimal' peristaltic stimulus were more sensitive to the effects of PGE1 than were preparations subjected to a 'just-maximal' peristaltic stimulus. The inhibition of peristaltic activity caused by perivascular nerve stimulation was antagonized by 0.56 microM PGE1 but slightly increased by 14 nM PGE1.

The effects of prostaglandins E1, E2, F1alpha and F2alpha on guinea-pig ileal and colonic peristalis

Prostaglandins (PGE1, E2, F1alpha and F2alpha) have been tested on the peristaltic reflex in isolated segments of guinea-pig ileum and colon using simultaneous recordings of fluid propulsion and longitudinal and circular muscle activity. Propulsion and circular muscle peristaltic activity were increased by serosally applied PGF compounds in the ileum and PGE or PGF compounds in the colon following initial contraction of the longitudinal muscle. This is consistent with a role for prostaglandins in peristalsis. Mucosally applied PGF compounds has no significant effect.

Effect of high concentrations of non-steroidal and steroidal antiinflammatory drugs on prostaglandin-induced contractions of the guinea-pig isolated ileum

In addition to their well-known effect at low concentrations on prostaglandin synthesis or their release and production, 11 non-steroidal antiinflammatory drugs and 4 antiinflammatory steroids exhibit at high concentrations a direct antagonism on certain prostaglandin actions. This is demonstrated on PGE1- and PGF2alpha-induced contractions of guinea-pig isolated ileum when compared to acetylcholine-induced contractions. This inhibitory effect is totally reversible after washing out the drugs from the organ bath.

Serum and bile modifications in the guinea-pig following chronic treatment with PGE1 and PGE2

PGE1 increases cholesterolemia without lipemia modifications. In bile there are not modifications in cholesterol levels and total lipids appear diminished. PGE2 raise the lipemia and have no effect in cholesterolemia, moreover bile cholesterol and total lipids exhibit no changes. Both PGE1 and PGE2 decreased the bile volume.

Inhibition of peristalsis in guinea-pig isolated ileum and colon by drugs that block prostaglandin synthesis

1 Methods of analysing peristaltic activity have been evaluated by the use of recordings of longitudinal and circular muscle activity and of propulsion in whole segments of guinea-pig ileum and colon. 2 Some prostaglandin synthesis inhibitors, and antagonists of prostaglandin action were tested for their suitability for studying the role of prostaglandins in peristalsis. Aspirin was suitable; at 10-200 mug/ml it had little effect on responses of longitudinal muscle strips of the guinea-pig ileum to acetylcholine (ACh), histamine, nicotine or prostaglandin E2. Indomethacin (1-4 mug/ml) reduced responses to nicotine and prostaglandin E2. The prostaglandin antagonists polyphloretin phosphate and SC-19220 reduced contractions of ileal longitudinal muscle caused by nerve excitation with either nicotine or transmural stimulation. 3 Aspirin (20-100 mug/ml) or indomethacin (1-4 mug/ml) applied serosally greatly inhibited all aspects of peristalsis in guinea-pig ileum and colon. Inhibition of peristalsis of the ileum by aspirin was antagonized by prostaglandin E2 and that by indomethacin was removed by prostaglandin F2alpha or ACh. Inhibition of colonic peristalsis by aspirin was antagonized by prostaglandin E2 but rarely by ACh, and that by indomethacin by prostaglandin E1 or E2. Mucosal application of aspirin had little effect on either ileum or colon but indomethacin caused some inhibition. 4 These results support the supposition that prostaglandins contribute to peristaltic activity.

Enteropooling assay: a test for diarrhea produced by prostaglandins

An assay (enteropooling assay) to test the diarrheogenic property of prostaglandins is described. Fasted rats are given a prostaglandins either orally or subcutaneously, and are killed 30 min later. The entire small intestine is removed and its contents collected into a test tube. The greater the volume of this intestinal fluid, the more diarrheogenic is the prostaglandin. The assay is simple, rapid, quantitative, and predictive of diarrhea. It can be used to grade the relative diarrhoegenic activity of prostaglandins as well as to test agents that may block this effect. The accumulation of fluid into the small intestine is called "enteropooling". It is the sum of (a) the fluid being excreted from the blood into the lumen, and (b) to a lesser extent, the portion of fluid already into the lumen but whose absorption is inhibited by the prostaglandin. The degree of enteropooling depends also on how much fluid flows from the small to the large intestine. Our results support the hypothesis that the diarrhea observed after administration of high doses of prostaglandins is due to accumulation of abundant fluid into the small intestine, and not intestinal hypermotility. This fluid is then carried into the large intestine and eventually expelled as diarrhea. Agents other than prostaglandins were tested for enteropooling activity. Laxatives such as castor oil, hypertonic solutions and bile salts caused enteropooling.

Intestinal pH and propulsion: an explanation of diarrhoea in lactase deficiency and laxation by lactulose

Subjects deficient in lactase may experience bloating, cramps and diarrhoea after ingesting milk, due to the unhydrolysed and poorly-absorbed lactose. The diarrhoea may result from an osmotic effect of the lactose itself or its poorly-absorbed acidic products of fermentation (Weijers, van de Kamer & others, 1961; Christopher & Bayless, 1971), possibly together with an alteration of sodium and water absorption due to the lowered colonic pH (Rousseau & Sladen, 1971). Laxation by lactulose (1-4-beta-galactosidofructose) may operate through an analogous mechanism. The drug is a synthetic dissaccharide which, in oral doses of 10-20 g, relieves chronic constipation (Wesselius-de Casparis, Braadbaart & others, 1968). It is neither hydrolysed by intestinal dissaccharidase (Dahlqvist & Gryboski, 1965) nor absorbed in the gut, but it is converted in the colon mainly to lactic and acetic acids by various bacteria including Lactobacillus acidophilus. Apart from the increased osmotic effect, the pH in the proximal colon falls markedly (Bown, Gibson & others, 1974), and larger doses may reduce stool pH. Weijers & others (1961) inferred that the acidic products formed from lactose in the colon stimulate propulsion, and K.S. Liem (Philips-Duphar) suggested to us that lactulose may relieve constipation partly by stimulation of propulsion due to the lowered pH. The experiments described below support this view.

Effect of prostaglandin F2 alpha on propulsive activity of the isolated segmental colon of the guinea-pig

The effects of prostaglandin F2alpha (PGF 2alpha) on propulsive activity in segments of isolated colon and on isolated strips of guinea-pig colon were investigated. Using experimental conditions under which spontaneous propulsive activity was negligible, PGF2alpha (5X10(-8)X1X10(-6)M), added to the bathing medium increased propulsive activity in a concentration dependent manner. This increase of propulsive activity was abolished in the presence of atropine or tetrodotoxin (1X10(-7)g/ml). The contractions produced by PGF2alpha (5X10(-7) -1X10(-5)M) in isolated longitudinal and circular smooth muscle strips of guinea-pig colon were unaffected in the presence of atropine or tetrodotoxin (1X10(-7) g/ml). From these results it is concluded that under the conditions employed in this study propulsive activity stimulated by PGF2alpha may depend on the contractions of both muscle layers and stimulation of the peristalic reflex.

Effects of E prostaglandins, diphenoxylate and morphine on intestinal motility in vivo

The mechanism of the gastrointestinal motility effects of diphenoxylate and morphine in preventing E prostaglandin (PG) diarrhea was investigated. Duodenal motility studies were conducted in the anesthetized dog. Two contractile force transducers were oriented to record contractions from both the circular and longitudinal muscles. In some experiments the basic electrical rhythm (BER) was also recorded. Blood pressure was monitored from the femoral artery and drug injections were made in the femoral vein. Diphenoxylate shared with morphine the capacity to stimulate circular muscle contractions which correlated with the appearance of spike potentials on the BER. Prostaglandin E1 methyl ester (PGE1ME) showed marked relaxation of the circular muscle and abolishment of spike potentials. PGE1ME also blocked the stimulatory effects of diphenoxylate and morphine on the circular muscle. PGE1ME and PGE2 were found to be equally potent in producing diarrhea in mice. Diphenoxylate and morphine were found to be equally potent in inhibiting PG's diarrhea. These studies suggest that the constipating actions of diphenoxylate and morphine are a consequence of the increased circular muscle activity of the intestine.

Uterine contractility and regional blood flow responses to oxytocin and prostaglandin E2 in pregnant rhesus monkeys

The effects of oxytocin and prostaglandin E2 (PGE2) infusions on regional blood flow (measured by radioactive microspheres) and myometrial contractility were studied in 18 pregnant rhesus monkeys near term. We observed no significant differences between PGE2 and oxytocin in cardiac output, hemodynamics, or uterine activity. Their effects on the regional distribution of systemic blood flow were similar although the gastrointestinal tract received an increased percentage of cardiac output after PGE2. A relative placental ischemia, together with a myometrial hyperemia, was observed during labor. Uterine contraction produced a large reduction (average 73 per cent) in placental blood flow whereas myometrial blood flow was maintained or sometimes increased. A significant negative correlation was observed between intra-amniotic pressure and placental blood flow. During uterine relaxation, placental flow partially recovered whereas myometrial flow nearly doubled the prelabor values. We conclude that (1) in the dose ranges studied, oxytocin and PGE2 produce similar effects on myometrial contractility and uteroplacental blood flow, and (2) the vascular beds of the placenta and myometrium respond differently to labor of moderate intensity.