Heparin, a highly sulfated and acidic glycosaminoglycan, has been clinically used in parenteral formulations to prevent and/or treat thromboembolic disorders for more than 90 years. Actions of heparin are not limited to anticoagulation and antithrombosis. Rather heparin has several other important actions which include fat clearing, antitumor and anti-inflammatory effects. However, use of heparin for such applications has been limited by its route of administration.<p>
Historically, it has been believed that heparin is not absorbed following oral administration and therefore is only available for clinical use by parenteral administration. This belief has been challenged several times by our laboratory and other researchers showing heparin binding to endothelium following oral administration as well as prevention of thrombosis and lowering blood pressure, etc. However, the site of oral heparin absorption and the mechanism responsible for absorption have not been investigated. This in vitro study was designed to address these important questions.<p>
We mounted pieces of rat gastrointestinal mucosa in a vertical diffusion Ussing chamber with both sides of the mucosal membrane exposed to Krebs bicarbonate buffer solution containing mannitol on the mucosal side (lumen) and glucose on the serosal side. Electrical properties across the membrane including potential difference (PD), resistance (R), and short circuit current (Isc) were recorded following heparin addition to the mucosal buffer under different mucosal buffer pH conditions. Mucosal and serosal buffer and tissue were collected and extracted for heparin and heparin recovery was performed by gel electrophoresis and anticoagulation tests.
The first chapter (chapter 4) was designed to investigate if stomach mucosal tissue is a site for unfractionated heparin (UFH) absorption when mounted in the Ussing chamber. We found that stomach mucosa is able to transport UFH in an intact form when both mucosal and serosal buffers are at neutral pH of 7.4. When the mucosal buffer pH is made more acidic, at pH 4, transport is facilitated.<p>
The second study (chapter 5) was designed to investigate if stomach mucosal tissue is also capable of transporting low molecular weight heparins (LMWHs). We showed that LMWHS were transported across stomach mucosa. However, the rate of transport was faster at mucosal buffer pH of 7.4 compared to pH 4.<p>
The third study (chapter 6) investigated the effect of molecular weight on rate of heparin transport across stomach mucosal tissue since pH dependency of this transport was evident from both previous studies. This study suggested that decreasing the molecular weight increases the rate of heparin transport across stomach tissue under neutral pH but not acidic pH conditions.
The fourth study (chapter 7) investigated how UFH is transported across the ileal mucosa and if Peyers patches contribute to this transport. It was shown that UFH is transported across ileal mucosa containing Peyers patches at a rate faster than ileal mucosa without Peyers patches. Making the mucosal buffer pH acidic facilitated UFH transport in the absence of Peyers patches but not when ileal mucosa contained Peyers patches.<p>
The final study (chapter 8) investigated the mechanism of UFH transport across stomach mucosa mounted in the Ussing chamber using pharmacological inhibitors sodium fluoride, colchicine, and amiloride. Results showed that UFH is transported across the stomach mucosa at physiological acidic pH by an active transport mechanism using metabolic energy, cytoplasmic tubule formation, and sodium-coupled systems.
From this, we conclude that oral heparins are absorbed across the gastrointestinal tract. The acidic environment of the stomach is a better absorption site for UFH. On the other hand, the more basic environment of the intestine is a better site for absorption of LMWHs. UFH is mainly absorbed across the stomach mucosa by an active transport mechanism using metabolic energy, cytoplasmic tubule formation, and sodium-coupled systems. Considering the very much larger surface area of the intestine than the stomach and that intestine, especially the ileum, contains many Peyers patches where UFH transport is not pH-dependent, larger amounts of UFH may be transported across the intestinal tissue compared to the stomach.
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-12232009-141235 |
| Date | 07 January 2010 |
| Creators | Moazed, Bita |
| Contributors | Linda, Hiebert M. |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-12232009-141235/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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