Recent studies have shown that when dehydrated rats are given access to water or various concentrations of saline solution, they consume the same volume of fluid in an initial drinking bout (Hoffmann et al., 2006). Furthermore, there was a close relation between fluid intake and distension of the stomach and small intestine when dehydrated rats drank water or saline (Hoffmann et al., 2006). These results are consistent with the hypothesis that fluid ingestion is constrained by a rapid inhibitory signal associated with GI fill. This volume-dependent early inhibition of thirst is reminiscent of the volume-dependent oropharyngeal reflex that Ramsay and colleagues described in dogs (Thrasher et al., 1981). Other studies (Huang et al., 2000) have shown that rats infused iv with hypertonic saline develop a strong motivation to consume water and show a marked increase in pVP. After water ingestion, pVP decreased rapidly before there was a change in systemic pOsm. Plasma VP remained elevated in rats that were given isotonic saline to drink. These results are consistent with the hypothesis that VP secretion is rapidly inhibited when dilute fluid enters the GI tract. The present studies sought to determine whether an early inhibition of fluid consumption by hypovolemic rats also was associated with GI fill. We imposed a 16-hr delay between the time that PEG solution was injected and the start of the drinking test. These animals have a substantial volume deficit (30-40%) as well as increased circulating levels of VP, OT, AngII, and aldosterone. Therefore, they have a pronounced thirst and salt appetite and will be eager to consume large volumes of fluid rapidly, thus allowing us to determine whether 1) distension of the stomach and small intestine provide a rapid inhibitory feedback signal for thirst and salt appetite, 2) gastric emptying of water or 0.30 M NaCl solution provide a presystemic signal that influences VP secretion, 3) changes in systemic pOsm influence ingestive behavior or VP secretion in rats with prolonged hypovolemia, and 4) GI fill continues to act as an inhibitory signal for fluid consumption after the first drinking bout.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-06272006-182200 |
| Date | 28 September 2006 |
| Creators | Smith, Carrie Alane |
| Contributors | Linda Rinaman, Edward M. Stricker, Alan Sved, Joseph Verbalis |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-06272006-182200/ |
| 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 Pittsburgh 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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