Angiotensin II and the control of humoral catecholamine release in fish.
The main goal of this thesis was to determine the relative importance of non-cholinergic secretagogues, primarily angiotensin II (Ang II), in the control of catecholamine release from the chromaffin tissue of fish. In rainbow trout (Oncorhynchus mykiss), immunohistochemical techniques and an in situ...
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| Format: | Thesis |
| Language: | unknown |
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University of Ottawa (Canada)
1998
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| Online Access: | http://hdl.handle.net/10393/4186 https://doi.org/10.20381/ruor-10135 |
| Summary: | The main goal of this thesis was to determine the relative importance of non-cholinergic secretagogues, primarily angiotensin II (Ang II), in the control of catecholamine release from the chromaffin tissue of fish. In rainbow trout (Oncorhynchus mykiss), immunohistochemical techniques and an in situ posterior cardinal vein (PCV) perfusion preparation provided direct evidence that Ang II can elicit catecholamine release from the chromaffin tissue via specific Ang II binding sites. Whereas the contribution of the renin-angiotensin system (RAS) to blood pressure recovery was largely indirect and relied on an Ang II-mediated secretion of catecholamines, the contribution from the sympathetic nervous system (SNS) was direct and relied on both plasma catecholamines and sympathetic nerves. In the American eel (Anguilla rostrata), injections of Ang II had no effect on humoral catecholamine release in either in situ PCV perfusion preparations or in chronically cannulated fish. The pressor effects of exogenous Ang II could not be attributed to any change in plasma catecholamine levels and the SNS does not appear to be an essential contributor to cardiovascular homeostasis during hypotension in the eel. The contributions of Ang II and humoral catecholamines to cardiovascular control were also investigated in an elasmobranch, the spiny dogfish ( Squalus acanthias). Whereas the contribution of catecholamines was direct, Ang II indirectly contributed to cardiovascular control by dose-dependent stimulation of catecholamine release. Results suggest that the control of catecholamine release from the chromaffin tissue of M. glutinosa can be achieved through hormonal and/or paracrine means and that ACTH, serotonin, and adenosine may all be involved. In summary, Ang II is a potent secretagogue of humoral catecholamine release in O. mykiss and S. acanthias. In both species, Ang II plays a significant role in the control of catecholamine release during acute hypotension, and this interaction represents an important physiological response for the maintenance of cardiovascular homeostasis. On the other hand, although previously suggested, Ang II does not appear to be a secretagogue of humoral catecholamine release in either A. rostrata or M. glutinosa. (Abstract shortened by UMI.) |
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