Summer 1999 Edition

Greetings (howdy) from Texas! This issue of the CGS newsletter contains a statement from the new president of the CGS (Dr. Allen Roussel), a statement from our outgoing president (Dr. Robert Washabau), an update on results of previous CGS grant awards, an overview of selected items from the Digestive Disease Week 1999 (annual meeting of the American Gastroenterology Association), and a report of the CGS-co-sponsored session at this same meeting.

For those of you who were unable to attend the ACVIM Forum in Chicago, the CGS-sponsored session on gastric mucosal injury, with emphasis on injury by NSAIDs, was well attended and the talks were excellent. Thanks to Drs. Frank Andrews, Colin Burrows and Denis McCarthy for their presentations. The CGS luncheon at the Forum (sponsored by Purina) provided an opportunity to recognize recipients of CGS-sponsored activities. Dr. Cynthia Webster, Tufts University, received the CGS Research Abstract Award for her abstract entitled, "Hepatocyte growth factor protection against bile acid induced apoptosis". Dr. Katharina Lohmann, Texas A&M University, won the CGS Young Investigator Research Abstract Award for her poster entitled, "Evaluation two methods for measuring gastric emptying in horses". The CGS Research Grant was awarded to Dr. Joanne Teetens for her study entitled, "The role of ATP in the maintenance of equine colonic epithelial tight junction integrity". Congratulations to these individuals and their co-investigators.

It is indeed an honor to serve as your CGS president for the coming two years as we enter a new millennium. I feel fortunate, yet somewhat anxious, to follow in the footsteps of Robert Washabau, whose leadership has resulted in several significant enhancements to our organization. Robert single-handedly moved us into the internet age by creating a CGS webpage (www.vet.upenn.edu/cs_phila/sam//cgs.htm). If you haven't visited it, I urge you to do so. It includes information on the CGS grant program, endoscopy courses and equipment, current and previous newsletters, and case discussions. Robert graciously volunteered to remain as the "webmeister." I'd like to extend a sincere "Thank you" to Robert for all the time, thought and work he put into CGS. As Past-president he will remain active in the leadership of the Society in the coming years.

On the subject of the internet, another of Robert's contributions is the CGS list-serve. This open channel of communication is available to us, but has been used only sparingly. I personally often forget it's there, but I hope all of us keep it in mind in the future. We don't need anymore "e-clutter", but there are certainly many legitimate issues and questions which would be appropriate for discussion among the group. Remember, research-related issues are welcomed and may be more important to many of us, as we have other lists upon which to discuss clinical matters.

Another new and ongoing project of our group, spear-headed by Colin Burrows and Al Merritt is involvement in the AGA's committee on DVMs, PhDs, and MD/PhDs. A few years ago, after this committee was formed, Colin and Robert urged us to join the AGA and increase the veterinary presence at the Digestive Diseases Week and in the association. I attended my first DDW this summer and was duly impressed. The CGS co-sponsored a half-day symposium this year on motilides and antimotilides which was outstanding. I counted at least 10 veterinarians in the audience. Thank you Colin and Al, and good luck next year. If you haven't heard, the committee has the charge of developing a program around the mouse as a model for G.I. disease. Colin would appreciate ideas on specific topics and speakers.

This is the first Newsletter being edited by Noah Cohen, my colleague down the hall. We are very fortunate to have someone with his editorial and organizational skills in charge. Noah has assumed a substantial responsibility by volunteering for this job. Please help him out by providing input and information to make the newsletter a useful tool. Noah, thank you for volunteering to serve CGS.

As I stated in my address to the membership luncheon in Chicago, this organization has the potential to be as much (or as little) as you, the membership want it to be. The officers are ready and willing to move in the direction in which you want to move. But we need input and guidance. Please let us know how we can serve your needs best, and we will strive to do so.

Statement from Dr. Robert Washabau, Outgoing President of the CGS

I wish to thank the C.G.S. membership for the confidence it showed me in electing me to the positions of President-Elect (1995-1997) and President (1997-1999) of the Society. I've completed those two terms of office, but I'm pleased to continue serving the Society in the capacity of Immediate Past President for the next two years. The Immediate Past President's major responsibility is to coordinate the grant review process. I expect to stay involved in a few other ways, as well:

(1) The C.G.S. WebSite - I initiated this effort about two years ago. The WebSite can always use fresh ideas from the membership. Please send me your ideas, and, of course, "visit our WebSite" at http://www.vet.upenn.edu/cs_phila/sam/cgs.htm. The WebSite contains the following listings: articles of incorporation, Society membership, Society Officers and Directors, membership application form, grant information and application form, notice of Society meetings, information on related Societies (AGA, CRWAD, ACVIM, etc.), newsletters, Society resources, summary of funded research proposals, ListServe discussion cases, and Society-endorsed Endoscopy Courses. Can I interest anyone in posting a case discussion?

(2) The ListServe - The Society has a new ListServe. This is a true ListServe, in that all messages (initiating and return) are seen by all members of the ListServe. The Society still has a System Alias that can be used to send messages to all members, but return messages are returned to sender only. The System Alias will likely have diminishing application with time.

(3) The A.G.A. - I believe the C.G.S. should have greater visibility in the American Gastroenterology Association. Colin Burrows and I have been advocating membership in the AGA for the past several years, and we've served as primary and secondary nominators for many membership applications. I will continue that advocacy in the coming years, and I will continue to support the Society's role in the AGA PhD, MD/PhD, and DVM Task Force. The Task Force has hosted several excellent programs on Comparative Gastroenterology in the past three years. Please read Dr. Al Merritt's 1999 Task Force summary at the end of this newsletter.

(4) The ACVIM - The C.G.S. should maintain, perhaps even increase, its visibility within the American College of Veterinary Internal Medicine. I've tried to elevate the visibility of the discipline during my tenure as ACVIM Forum Program Chair (1998-2000), and I will continue that effort as ACVIM-Internal Medicine Specialty President (2000-2003).

(5) Fellowships - As part of its research mission, I believe the ACVIM should participate in the development and sponsorship of post-residency training fellowships in the Internal Medicine sub-specialties, e.g., gastroenterology, endocrinology, nephrology, etc. These sub-specialties have matured over the past decade, and there is a clear need in academic medicine for further research training not provided by the traditional research programs. ACVIM-sponsored fellowships could be of one- to three-years duration, depending upon trainee interest and needs. As Internal Medicine Specialty President, I hope to engage the officers and memberships of the Comparative Gastroenterology Society, Society for Comparative Endocrinology, and Society for Veterinary Nephrology/Urology in moving this process forward.

On a final note, please join me in thanking Dr. David Williams for his six years of service as President-Elect (1993-1995), President (1995-1997), and Immediate Past President (1997-1999). Congratulations on your many fine efforts, Dave, and good luck with the program at Texas A & M.

One of the major projects of the GCS, and one in which we have a great deal of pride, is the CGS Grant Program. This program, which has been generously supported by Hills Pet Nutrition, provides funding for developing gastroenterologists who are working with CGS members. The following is a brief synopsis of the results from our 1996 and 1997 grant recipients.

The 1996 recipient was Dr. Nancy Witters of the University of Nebraska-Lincoln who's CGS mentor was Dr. Gerald Duhamel. The title of her proposal was "Colonic Mucin Association of Serpulina pilosicoli in Canine Intestinal Spirochetosis." In the first of 2 studies, the investigators studied the role of D-L serine or porcine gastric mucin (PGM) in the chemotaxis of a human, a porcine and a canine strain of S. pilosicoli. Chemotaxis was expressed as the ratio of the number of spirochetes present in the capillary tubes containing the attractant divided by the number in the control tube. A significant chemotactic response to D-L serine was found to the porcine isolate while the human and canine strains were attracted to PGM. The data indicate variation in chemotactic response of S. pilosicoli, but the authors concluded that the similarity between the human and canine isolates suggests a zoonotic potential for the canine isolate.

In the second study, the same isolates were grown with or without pig fecal extract, then examined for a chemotactic response to D-L serine or PGM. The loss of chemotactic response caused by removing the pig fecal extract from the growth media was restored by adding 0.1% PGM to the growth media. This indicates that the chemotactic response is inducible by the addition of a chemotactic substrate during the growth phase of the spirochete. Two abstracts resulted from this work. Congratulations to these investigators for their fine work.

The 1997 recipient was Dr. Mustajab H. Mirza of Louisiana State University who's CGS mentor was Dr. Rustin Moore. Other collaborators included Drs. T. L. Seahorn, J. L. Oliver, and G. Hosgood. The title of his proposal was "The Role of Nitric Oxide in the Pathophysiology of Strangulating Obstruction of the Large Colon in Horses." The objective of this project was to determine whether nitric oxide (NO) is present in clinically normal horses under basal conditions, and if it increases secondary to naturally acquired large-colon volvulus. They compared 11 adult horses with naturally acquired large-colon volvulus and 10 clinically normal horses. Jugular venous blood, abdominal fluid and urine and analyzed for NO. A biopsy specimen was collected from the pelvic flexure of the large colon at surgery or after euthanasia and divided into subsections for fixation in zinc formalin and cryopreservation in OCT gel. NADPH diaphorase histochemical stains were performed on cryopreserved tissues and inducible nitric synthase (iNOS) and nitrotyrosine immunohistochemical stains were performed on formalin-fixed, paraffin-embedded tissues.

There were no significant differences between control and affected horses for urine, plasma, or abdominal fluid NO concentrations. There was a significant decrease in submucosal venular endothelium and submucosal plexus NADPH diaphorase staining in horses with large-colon volvulus, compared with control horses. There was a significant increase in iNOS staining in mucosal and submucosal leukocytes in horses with large-colon volvulus, compared with controls. There were no significant differences between affected and control horses for nitrotyrosine staining.

The investigators, conclusions were that endothelial NOS and neuronal NOS are present under basal conditions in the large colon of horses. Plasma, abdominal fluid and urine NO concentrations were not increased subsequent to large-colon volvulus. Most of the affected horses in this study were euthanatized during surgery or shortly after the correction of large-colon volvulus, resulting in a short duration or no reperfusion. Ischemia followed by reperfusion of a longer duration may have led to increased systemic concentrations of NO. However, it is possible that iNOS is not activated by the same mechanism(s) as in other species.

Dr. Mirza funded part of his Master's thesis research with the CGS grant and subsequently has submitted a manuscript for publication, had 2 abstracts published and made 5 poster presentations. We congratulate Dr Mirza and his colleagues for this fine work.

I think these projects are outstanding examples of the quality of proposals and investigators from which we have had to chose in recent years and contribution CGS can make to the development of future gastroenterologists.

The digestive disease week was held in Orlando this year. In the following I would like to share a few selected impressions and tidbits I gathered.

First, I participated in a workshop offered by the American Association for the Study of Liver Diseases (AASLD) about clinical trials research. Dr. Friedman from the NIH gave a brief introduction into clinical trials. He outlined the different phases of clinical trials. While I was familiar with phases I, II, and III I had not realized that there is actually a phase IV that is directed at the study of a drug that has already gone through the other phases, but in other populations or for a different applications. He also reflected about common pitfalls of clinical trials. During planning of a trial lack of clear objectives, over-enthusiastic goals, or inadequate resources can jeopardize the success of the trial. Then, during conduct of the trial, poor enrollment, lack of adherence to the protocol, and missing data can lead to failure of a trial. Finally, during analysis and reporting poor quality data, exuberant interpretation of results, and a reporting bias all could cause an unsuccessful outcome of a trial. I am sure that we all have been faced with one or the other of these pitfalls.

Dr. Cramer from Yale University was expanding on the matter of lack of enrollment. Apparently there is a law that describes the occurrence of uncommon disorders: Lasagna's law. This law states that as soon as one starts to study a particular disease the incidence of that disease appears to decrease sharply while after one closes enrollment into the trial the incidence once again rises sharply. Of course this phenomenon only occurs in the perception of the investigators and is just a reflection of the limited number of patients that would actually pass inclusion criteria for the study. In other words the incidence of the diagnosis of a disease remains the same yet the diagnosis may not withstand scientific scrutiny or patients may have complicating conditions that one can not control for during statistical analysis. Dr. Cramer also expanded on the topic of patient compliance. Studies have shown a compliance rate of 63-85% in highly motivated human patients. Clearly, the compliance rates in less motivated patient groups would be disastrous. Studies have also shown that patients are usually not devious. They may decide not to take a medication and discard the medication instead before presenting the pill bottle for a pill count to the physician but they will not open the bottle every time they should take the medication and then discard the medication. This means that counting and mapping the opening of the pill bottle will accurately determine whether or not a patient is compliant.

Aardex is now offering a device that will count and map the openings of the pill bottle. The data is stored in the cap of the pill bottle and can be read with another device installed onto a computer system (website: aardexus.com).

Another speaker, Dr. Heathcote from Toronto Hospital was talking about sample size and power. I have to admit that this topic has never made much sense to me because it seems that there is no difference in choosing a random number of samples and choosing a random expected effect and calculating the number of samples needed from this randomly estimated expected effect size. And in all reality there isn't. For studies in human medicine sample size calculation is indeed an important consideration. This is because virtually every large clinical trial is preceded by a pilot study enrolling maybe only 6 to 20 patients. Results from this pilot study will be reasonable grounds for estimating expected effect size and will in turn be a solid basis for the calculation of the sample size needed in order to accept or reject a hypothesis. One should however realize that clinical trials in veterinary medicine usually are more comparable with pilot studies in human medicine and usually do not allow reasonable sample size calculations. (Editors Note: Not all veterinary clinical trials are experiments with small numbers of animals. These topics of sample size are equally apt to veterinary medicine).

Dr. Schuster from Veterans Affairs in Philadelphia delivered a plea for strengthening informed consent standards for clinical trials, which was not really significant for veterinary medicine. (Editors Note: Many veterinary teaching hospitals require informed consent for clinical studies involving patients). However, it led to the important question of whether one can ever reach statistical significance ethically. As a doctor, is the investigator ethically bound to disclose any trend to a patient who is willing to enroll? In other words is a doctor that observes a trend of improved outcome when using one drug obliged to offer that treatment without enrolling the patient in the blinded study? I think these are questions that must be carefully evaluated for every clinical trial in human or veterinary medicine alike. However, the knowledge that psychological factors cause benefits to patients enrolled in a trial regardless of assignment to a particular treatment group may make the decision to continue a blinded trial easier.

One last area that was presented in detail was the economic impact of clinical trials. The pharmaceutical industry has been a growth industry for the last 50 years and will probably remain to grow as health care is getting more sophisticated and health care systems are established in developing countries. Gross sales for single products can amount to enormous sums. For example, the daily gross sales for omeprazole (Prilosec®) amount to $11.2 million per day, or $4.1 billion a year. The average expenditure of drug companies for development of a new drug is currently 20.8% of gross sales. This illustrates that substantial amounts of money are available for clinical trials. This has led to the development of a new clinical trials market. Pharmaceutical companies often don't conduct clinical trials themselves any more, but subcontract with private companies. These companies develop the trial protocol and have it reviewed by a central institutional review board. Currently there are approximately 3000-5000 local and 12 central institutional review boards. Central institutional review boards are commercial and review a large number of protocols. Private research companies conducting a trial for a pharmaceutical company will also take bids from academic institutions and private practices for participation in those studies. In human medicine private practices are now routinely participating in clinical trials and they are paid well to do so. Private research companies actually often prefer to work with private practices because adherence to the research protocol has been shown to be better and reporting of patient data appears to be more consistent. While this information may sound like no more than an interesting human medical tidbit I think it leads to the important question how successfully veterinary academic institutions or private practices are prepared to be a competitive bidder for quality clinical trials participation should the veterinary clinical trials market become more competitive.

A total of 5945 scientific abstracts were submitted for this years digestive disease week and approximately 5000 of those were presented orally or as most of them in a poster format. It would be ambitious of me to try to summarize all of the information presented. However, I would like to share a few interesting ideas with you.

One of the hottest topics in human gastroenterology is undoubtedly imfliximab (RemicadeÔ). Imfliximab is a chimeric IgG1 monoclonal antibody directed against human tumor necrosis factor alpha (TNF). Imfliximab has been shown effective in the treatment of different groups of patients with Crohn's disease, such as patients with corticosteroid-dependent disease, patients with fistulating Crohn's disease (Gastroenterology 116 (4,2) G3420, 1999), or patients with moderate or severe Crohn's disease (Gastroenterology 116 (4,2) G3636, 1999). Long-term use of imfliximab has also been shown to be safe (Gastroenterology 116 (4,2) G3528, 1999). Unfortunately, the use of this drug in dogs or cats with inflammatory bowel disease is probably not indicated because these species would undoubtedly form antibodies against these human/mouse chimeric antibodies. The repeated use of this medication would therefore be prohibited. Two other potential therapeutic options that are based on decreasing TNF are the use of thalidomide and TACE (TNF converting enzyme). Thalidomide has showed improved clinical signs in 9/10 patients with treatment-resistant inflammatory bowel disease (Gastroenterology 116 (4,2) G3327, 1999). Side effects included mild sedation, xerostomia, skin dryness, and constipation. However, another group of investigators failed to show any significant effect of thalidomide on inflammatory activity of Crohn's disease, but did show that the drug was efficacious in patients with severe GI bleeding (Gastroenterology 116 (4,2) G3327, 1999). The manufacturer of thalidomide is extremely cautious about release of the drug and clinical trials in veterinary species are not considered at this point.

There was also some new data about the use of budesonide in patients with Crohn's disease. In a Swedish study ileal controlled release capsules of budesonide (Entocort®), a nonsteroidal antiinflammatory with high topical anti-inflammatory activity and an extensive hepatic first-pass effect was studied in four children and four adults with Crohn's disease (Gastroenterology 116 (4,2) G3405, 1999). Unfortunately, this study did not provide any new data concerning the clinical efficacy of this drug, but rather reported about the pharmacokinetics of the controlled-release capsules. Another study reported about the use of budesonide in patients with Crohn's disease after colectomy and ileostomy (Gastroenterology 116 (4,2) G3812, 1999). Oral budesonide significantly reduced intestinal volume in these patients suggesting that budesonide has an activity independent of its antiinflammatory effect.

Another area of interest was the use of probiotic Lactobacillus spp. One study evaluated the use of Lactobacillus GG on antibiotic-associated morbidity in patients treated for Helicobacter pylori infection (Gastroenterology 116 (4,2) G0494, 1999). This group found a decrease of gastrointestinal side effects, such as belching, bloating, and nausea in these patients. Another study suggested an immunomodulatory effect of Lactobacillus GG (Gastroenterology 116 (4,2) G3537, 1999). Yet another study showed that Lactobacillus plantarum was superior to Lactobacillus GG in preventing colitis in IL-10 -/- mice after exposure to SPF flora (Gastroenterology 116 (4,2) G3642, 1999).

There were no new data about the use lexipafant and other platelet activating factor inhibitors in patients with acute pancreatitis this year. This would make one suspicious that the large multinational multicenter trial scheduled to be finished last fall did not produce the expected results. One abstract reported about admission hematocrit as a predictor of pancreatic necrosis in patients with pancreatitis (Gastroenterology 116 (4,2) G5097, 1999). An admission hematocrit of £ 40 was associated with not developing pancreatic necrosis in both community and university hospital based patients with pancreatitis. Whether admission hematocrit would also be a useful predictor of disease severity in canine or feline pancreatitis patients remains to be determined.

The effect of storage on breath samples has always been a concern. One study evaluated the effect of storage on ¹³C urea-breath samples over a period of 2 years at room temperature and found the measurements to be reproducible even after such a long time period (Gastroenterology 116 (4,2) G1274, 1999). While the implications for veterinary medicine may not be immediately apparent this information may become more important as the use of breath tests is being investigated in veterinary species.

Another topic of several abstracts was the use of argon plasma coagulation (APC). One abstract reported the use in a total of 1454 patients (2795 applications) (abstract 3337, not published in Gastroenterology). The technique was used in patients with malignancies (n=772), bleeding (n=360), adenomas (n=215), stent ingrowth (n=160), and angiodysplasia, watermelon-stomach, radiation injury or other conditions. The method proved highly effective, safe, and easy to perform. This technology can be performed via the working channel of any standard endoscope. The equipment needed costs approximately $ 25,000 and may therefore be affordable for tertiary veterinary care centers for evaluation.

Finally, one striking abstract was reporting about the comparison of biopsy interpretation between community and academic pathologists (Gastroenterology 116 (4,2) G0408, 1999). Specimens were evaluated by a community-based pathologist and reviewed by two hepatopathologist and one hepatologist. In 42.6% of all specimens there were discrepancies that consisted of an altered description or diagnosis that would change management decisions. In an additional 10% there were minor differences. Major discrepancies were more common in patients with cholestatic disorders (71%) than in patients with hepatocellular processes (40%). This study would suggest that one should be extremely careful in the selection of a pathologist for evaluation of hepatic specimens.

The above can only serve to give you a glimpse at the wealth of novel ideas and strategies presented at this years digestive disease week. However, I hope that it may spike your interest in this outstanding meeting or in joining the American Gastroenterology Association.

CGS Co-Sponsored Symposium at This Year's AGA Meeting (prepared by A.M. Merritt)

At the annual meeting of the American Gastroenterological Association held in Orlando FL on May 15-19, 1999, the CGS, along with the PhD,MD/PhD,DVM Committee and the Motility and Nerve Gut Interactions section within the AGA, co-sponsored a symposium entitled: Current Topics in Comparative Gastroenterology: Animal Models and Motilide Receptor Heterogeneity: Motility vs. Transit. The symposium was organized by me and co-chaired by myself and C.F. Burrows. While the existence of a peptide, called motilin, which appears to be involved in the endogenous modulation of the migrating motility complex (MMC), was first isolated by Brown et al. in 1971 , it has only been recognized within the last 15 years that various other compounds, including the antibiotic, erythromycin, can cause similar effects on GI motility. Much of the pioneering investigation of the motilide-like effects of erythromycin was done in the laboratory of Professor Itoh in Japan. More recently, the motilin receptor has been cloned, due largely to the work of Peeters and his group in Belgium, and as more studies have been done with erythromycin, its analogues, and other putative motilides, it has become increasingly clear that their effects have not been uniform with respect to species, effective dose and site along the GI tract.

Therefore, I thought it might be a good time to try to pull this all together and was fortunate enough to persuade some of the leaders in the field to participate. I was particularly interested in touching on not only the business about receptor heterogeneity, but also the concept that increased motility does not necessarily translate into increased transit of contents along the tract. I kicked things off with a short Introduction and was followed, in order, by Dr. Sushil Sarna from the Medical College of Wisconsin in Milwaukee who is one of the giants in the GI motility field in this country; Dr. Theo Peeters from the Gut Hormone Lab at the University of Leuven, Belgium who has published extensively on the effect of motilides in humans and numerous species of animals, and; Dr. Charles Malbert from the INRA Station des Recherches Porcines in St. Hyacinthe, France who is among the group of younger investigators in the field and has been a pioneer in the use of swine for GI motility studies. Below is an abstract of each of the presentations that was written by the respective speakers prior to the symposium. It should give good representation of the material that was covered:

Introduction

A.M. Merritt

There are mixed reports regarding the effect of erythromycin on gastric emptying rate in dogs. In this study the effect of three dosage levels of erythromycin lactobionate on solid phase gastric emptying in normal dogs was evaluated by scintigraphy. Hill's Canine Maintenance® labelled with 99mTc-disofenin was the meal used for imaging.

Five healthy mixed breed dogs that had been accommodated to the base diet at a maintenance rate of 50 Kcal/Kg/day, and pre-conditioned to the imaging proceedure, were used. Each dog received five treatments in a randomized block sequence, one treatment per given experiment, just after ingestion of the meal. Treatments were: lactated Ringers solution (LRS), or Na-lactobionate at 50 ug/kg or erythromycin lactobionate at 25, 50, or 100 ug/kg total dose dissolved in LRS. A total volume of 10 ml was administered intravenously via a cephalic vein catheter over a 30 minute period, using an infusion pump. Infusion began immediately after the baseline scintigraphic image was obtained. Images were then obtained at three minute intervals for the first 15 minutes, and subsequently at 20, 25, 30, 45, 60, 90,120,150, 180, 240, 300, and 360 minutes post-feeding.

Power exponential curves were constructed from each data set and the ß (shape parameter of the curve describing initial emptying and T50 ( time when 50% of marker has emptied) were derived from each curve. No significant difference was detected between treatment groups. We conclude that erythromycin lactobionate treatment at between 25-100 ug/kg has no effect on solid meal gastric emptying rate in the normal dog.

In horses, however, Lester et al have demonstrated, by scintigraphy that erythromycin lactobionate at 0.1 mg/kg will significantly increase both gastric and cecal emptying rate of a "solid" meal. The effect on the cecum was more dramatic than on the stomach. The suggestion is made that perhaps animals that depend upon hind gut fermentation to digest a good portion of the ingested food have a greater density of motilide receptors in their large intestine than do those animals where most of the food is digested and absorbed by the small intestine.

Sushil K. Sarna

The efficacy, potency and specificity of prokinetic agents in accelerating transit differ in different organs of the gastrointestinal tract. We investigated whether this is due to their different enteric locus of action and receptor subtype utilization. We compared these for motilin, erythromycin and ABT-229 in stimulating jejunal circular muscle contractions in intact conscious dogs by close intra-arterial infusions, in muscle bath and in single enzymatically dispersed cells. In the intact conscious state, all three agents stimulated phasic contractions but no giant migrating contractions. The order of potency was: motilin=ABT-229>erythromycin, and order of efficacy: motilin=ABT-229>erythromycin. The responses to all agents were blocked almost completely by atropine, hexamethonium, tetrodotocin, and M₃ receptor antagonist 4-DAMP, M₁ receptor antagonist, pirenzepine, only partially blocked the response only to ABT-229. 5-HT_1A, 5-HT₂/5-HT_1C receptor antagonists had no effect on the responses to motilin and erythromycin. Only 5-HT₂/5-HT_1C receptor antagonist LY-53,857 partially blocked the response to ABT-229. NK1, NK2 and NK3 receptor antagonists had no effect on the response to motilin, but each of them partially blocked the response to ABT-229. Only NK2 and NK3 receptor antagonists partially blocked the responses to erythromycin. In contrast to the above, none of the prokinetic agents stimulated contractions in circular muscle strips or ex-vivo segments. However, each of them concentration-dependently contracted single dispersed cells. Each of these responses was blocked concentration dependently by motilin antagonist, Phe-3, Leu-13 porcine motilin. (Kindly supplied by Dr. Theo Peeters). This motilin antagonist also reduced the response to motilin, ABT-229, and erythromycin in intact dogs, but the attenuation was not statistically significant.

In conclusion, all three prokinetic agents act on presynaptic neurons to stimulate phasic contractions. Erythromycin is less potent than ABT-229, which is less potent than motilin. Each prokinetic agent may act on a different subset of presynaptic neurons and the response is mediated by different muscarinic, serotonergic and tachykininergic receptors. The presynaptic neurons on which the prokinetic agents act converge on postsynaptic cholinergic motor neurons. The final neurotransmitter at the neuroeffector junction is acetylcholine. All prokinetics utilize at least one nicotinic synapse which is not in parallel with any other receptor. The presynaptic neurons seemto be impaired in the muscle bath environment.

Neurogenic and Myogenic Effects of Motilides: Relation to

Motilin Receptor Heterogeneity

T.L.Peeters.

In vitro motilides predominantly activate a smooth muscle motilin receptor. This receptor has been characterized in contractility and in binding studies. Early circumstantial evidence that motilides are agonists for this smooth muscle receptor was definitively confirmed with the development of the first motilin antagonists. Recent observations however show evidence for neurally mediated in vitro effects. Also, while binding studies have been assumed to reveal smooth muscle receptors, recent data associate binding with synaptosomes. Binding studies have also detected central, and therefore neural, motilin receptors. They may be related to peripheral neural motilin receptors.

In vivo, most effects of motilides are neurally mediated. However the same the same applies to motilin and both substances seem to act on neural pathways to increase the release of acetylcholine and other excitatory transmitters. These pathways may differ in the fasting and the fed state. Nevertheless some in vivo responses may be mediated via the smooth muscle receptor.

The discrepancy between in vivo and in vitro results is probably due to differences in affinity of the smooth muscle motilin receptors and the motilin receptors present on neurons. This indicates that there must be at least muscular and neuronal motilin receptors, but species and organ subtypes seem to exist as well. Although as yet no true specific agonists or antagonists have been developed, the effort may be worthwhile and have therapeutic applications. The undesirable side-effects of motilides when applied as prokinetics may well be due to their effect on fundic motilin receptors, which seem to differ from antral and colonic receptors. While a specific agonist for the fundus could have other applications, a prokinetic agent acting solely on the antral pump could have an interesting potential.

Erythromycin-Induced Gastrokinesis in Swine: Motility vs Emptying

C.H. Malbert

Erythromycin is the leading molecule of the motilide family currently being used to promote gastric emptying of liquids and solids in various pathologic conditions that cause gastroparesis. While its clinical efficacy cannot be questioned, its mechanisms of action in intact subjects are still controversial. In conscious pigs, erythromycin increased transpyloric flow of liquids but not solids, thus demonstrating meal-dependent effects which would not be appreciated by recording erythromycin-induced gastropyloroduodenal motility alone. Vagal integrity was essential for the increase gastric emptying of liquids to occur, whereas gastric motility was similarly increased irrespective of the vagal status. Finally, erythromycin modified the sensitivity of slowly adapting fundic vagal sensory receptors and decreased their activation threshold during isobaric gastric distension. This effect did not relate to erythromycin-induced motor effects since it persisted while wall tension was maintained constant. In conclusion, these discrepancies exemplify our present inability to predict gastric emptying rate from a given motor pattern. Furthermore, the alteration of vagal sensory receptor activity by erythromycin might actually impair symptomatic recovery in gastroparetic patients, despite its demonstrated gastrokinetic effects.

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