Then, from the spreading of the observed breakthrough curve, we can estimate the unknown, the pore-scale transverse dispersion. The measured quantity varies inversely with the transverse dispersion coefficient. The project is near completion and a Ph. Highlights of the dissertation: We discuss instrumentation and tracers that we used to obtain experimental concentration breakthrough curves. We describe the numerical simulation and parameter estimation methods used to analyze the experimental data.
We discuss the results and describe the relative advantages of each device, instrument, and methodology that we have used to estimate transverse dispersivity. Perhaps the most noteworthy conclusions of this research are that the results from the two devices, helix and cochlea, are in agreement and that the ratio of transverse dispersivity to longitudinal dispersivity that we estimate agrees with the higher ratios reported in the literature. Fluid residence times within a recirculation zone created by an extraction-injection well pair.
Journal of Hydrology ; Temporal-moment matching for truncated breakthrough curves for step or step-pulse injection.
Advances in Water Resources ;29 9 The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency. Jump to main content. Contact Us. Project Research Results Final Progress Report Original Abstract 6 publications for this subproject 2 journal articles for this subproject Main Center: R publications for this center 60 journal articles for this center.
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All 6 publications. Several mechanisms, including the hypermotility of the stomach, have been proposed to explain indomethacin-induced gastric ulceration[ 1 - 4 ]. Hypermotility may be due to the action of drugs on the CNS, or peripheral effects of indomethacin on the stomach nerves or muscles. In the present study, we have investigated the effects of indomethacin on the contractile responses of the isolated transverse and longitudinal strips of rat gastric fundus to myenteric plexus activation via EFS. The fact that atropine prevented the EFS-induced strip contractions suggests that the contractions originate, at least in part, from the cholinergic system.
According to the present results, the responses of transverse and longitudinal strips to indomethacin were not identical. In the transverse strips, the effect of indomethacin was inhibitory while in the longitudinal strips, the response to indomethacin was dependent on the concentrations of the drug. We observed an increase in the amplitude at the low concentrations, while a decrease in the amplitude at higher concentrations. Takeuchi et al[ 1 , 2 ] and Ueki et al[ 3 ] in in vivo studies, demonstrated that indomethacin administration resulted in a significant gastric hypermotility.
In our experiments, contrary to the hypermotility reported by the aforementioned investigators, we observed relaxation of the strips after indomethacin administration. It is possible that the reported results are the net effect of several different factors; some of them are not limited to the stomach and are systemic effects. Gastric motility is under the control of neural, humoral, and mechanical factors with stimulatory or inhibitory effects on the stomach contractility.
The net results of these effects will determine the contractility of the stomach. The strip relaxation may be due to the inhibition of stimulatory prostaglandins PGs [ 12 , 13 ], L-type calcium channels[ 14 ] or phosphodiesterase 4[ 15 ]. The presence of the K ATP channels has been demonstrated in the smooth muscles of the stomach[ 16 ].
The difference between the results obtained in transverse and longitudinal strips following indomethacin administration may be dependent on the state of K ATP channels of the tissues.
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Opening of the channels by diazoxide, in the longitudinal strips, resulted in responses similar to that of transverse strips under indomethacin treatment. On the other hand, the administration of glybenclamide, a K ATP channel antagonist, interestingly, changed the response of transverse strip to a response similar to that of longitudinal strips under indomethacin treatment.
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Altogether, these results are suggestive of the possible role played by K ATP channels on the effects of indomethacin on the motility of the isolated rat gastric fundus strips. The stomach is one of the sources of different types of PGs with stimulatory or inhibitory effects on contractility of the organ[ 17 ].
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It has been known that indomethacin has inhibitory effects on the generation of PGs. On the other hand, the effects of PGs are known to be through their receptors[ 18 ]. Some PG receptors are only present in the longitudinal muscles[ 19 ]. This also may explain the difference between the results obtained in longitudinal and transverse strips as observed in our present study.
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As shown in Figure 3 , the stimulatory effect of indomethacin on the EFS-induced contraction of the longitudinal strip was abolished by both diazoxide and glybenclamide. These drugs have an opposing effect on K ATP channels: diazoxide has an ability to open the channels while glybenclamide has an ability to inhibit the channels. Because K ATP channel opener induces relaxation of smooth muscle through hyperpolarization, it is easy to understand the effect of diazoxide.
However, glybenclamide causes depolarization through inhibition of K ATP channels and results in activation of the cell contraction. Yet, this agent abolished the stimulatory effect of indomethacin on the EFS-induced contraction of the longitudinal smooth muscle. It seems that glybenclamide acts more than a K ATP channel blocker, thus other possible mechanisms for this action of glybenclamide must be evaluated.
In conclusion, the pattern of response of transverse and longitudinal strips to indomethacin is not quite similar, which may be due to the involvement of K ATP channels. However, the overall effect of indomethacin on EFS-induced contractions of the isolated strips of rat gastric fundus is an inhibitory action.
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Citation of this article. Effect of indomethacin on electrical field stimulation-induced contractions of isolated transverse and longitudinal rat gastric fundus strips. Corresponding Author of This Article. Article-Type of This Article. Brief Reports. Open-Access Policy of This Article. This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. Number of Hits and Downloads for This Article.
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World J Gastroenterol. Author contributions : All authors contributed equally to the work. Correspondence to : Dr. Strips response to cumulative concentrations of indomethacin. Relaxations are expressed as percentages of the amplitude of contractions induced in the same strip by EFS before drug treatment. The responses of transverse and longitudinal strips of rat gastric fundus for each concentration of indomethacin were compared. Effects of K ATP channel modulators on responses to indomethacin.
Relaxations or early contractions are expressed as percentages of the amplitude of contractions induced in the same strip by EFS before drug treatment. Importance of gastric motility in the pathogenesis of indomethacin-induced gastric lesions in rats. Dig Dis Sci. Functional mechanism underlying COX-2 expression following administration of indomethacin in rat stomachs: importance of gastric hypermotility. Gastric motility is an important factor in the pathogenesis of indomethacin-induced gastric mucosal lesions in rats.
Analysis of pathogenic elements involved in gastric lesions induced by non-steroidal anti-inflammatory drugs in rats. J Gastroenterol Hepatol. Permissive role of neutrophils in pathogenesis of indomethacin-induced gastric lesions in rats.