The present study provided information for the role of the RAS in seabream osmoregulatory responses. The structure of angiotensinogen suggested that flounder type Ang II was the prevalent form in seabream. However, HPLC analysis suggested that different forms of angiotensins were present in seabream adapted to different salinities. The status of RAS was revealed in seabream adapted to different salinities and a higher status was found in hypersaline environment. Local renal RAS was identified and it may be activated in hyposmotic media and associated with an increase in glomerular and tubular function to excrete excess water. In general, the RAS in seabream displays differential status, both at systemic and local levels, which modulates osmoregulatory functions under acute and chronic salinity perturbation. / The renin angiotensin system (RAS) is involved in the control of body fluid homeostasis in silver seabream. Seabream angiotensinogen was cloned and sequenced in the present study. The sequence alignment showed that the angiotensinogen of seabream is most similar to that of pufferfish. Differential status of RAS was found among different salinities, with relatively higher RAS activity among hyperosmotic adapted seabream. Circulating angiotensin II (Ang II) was higher in hyperosmotic adapted seabream, with the highest value observed in seabream adapted to double-strength seawater. Although the level of immunoreactive angiotensins in freshwater adapted seabream was higher than that of brackish-water, Ang III, but not Ang II, was the prevalent circulating form in freshwater adapted seabream according to HPLC analysis. Hepatic angiotensinogen expression, however, did not show any statistical difference among different salinities. A positive feedback control for angiotensinogen by Ang II is present in the hepatic tissue of seabream as Ang II increased the expression of angiotensinogen in isolated hepatocyte but captopril lowered the angiotensinogen expression in intact fish. Branchial Na-K-ATPase activities were elevated by Ang II and the activities among different salinities showed a pattern similar to that of circulating angiotensins. However, upon abrupt hyposmotic transfer, branchial Na-K-ATPase elevated along with a decrease in circulating Ang II, an observation implying that the relationship between Na-K-ATPase and Ang II may only be causal. Captopril blockade not only lowered not only circulating Ang II levels but also that of cortisol, indicating RAS activity may limit cortisol secretion. An elevation in the circulating cortisol may be related to the increase in branchial Na-K-ATPase activities after abrupt hyposmotic transfer. The stimulatory effect on branchial Na-K-ATPase activity and the vasopressor effect of Ang II were more potent in hyposmotic than hyperosmotic adapted seabream, which indicates hyposmotic adapted seabream is more sensitive to RAS activation. The renal RAS in silver seabream functions independently from the systemic RAS as the pattern of renal angiotensins was dissimilar to that of systemic angiotensins. The renal RAS was activated in brackish water conditions and abrupt hyposmotic transfer significantly increased renal RAS activities. Kidney morphometrics also indicated that hyposmotic adaptation increase the filtering capacity of seabream nephrons. The number and diameter of glomeruli increase significantly in freshwater adapted seabream, which may vastly increase the filtering surface of the nephrons. Collecting tubules were more prevalent in the kidney of hyposmotic adapted seabream, with higher number, diameter and thickness, suggesting a lower water permeability of collecting tubules is essential for the formation of copious and diluted urine in hyposmotic environment. / Wong Kwok Shing. / "December 2005." / Adviser: Norman Y. S. Woo. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6144. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 130-145). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_343721 |
| Date | January 2005 |
| Contributors | Wong, Kwok-Shing., Chinese University of Hong Kong Graduate School. Division of Biology. |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, theses |
| Format | electronic resource, microform, microfiche, 1 online resource (147 p. : ill.) |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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