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Thirst and brain angiotensin in cattle.
J R Blair-West1, D A Denton, M J McKinley
1Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Australia.
The American Journal of Physiology
|February 1, 1992
Summary
Brain angiotensin plays a role in thirst in cattle. Angiotensin II may be formed within the brain, independent of converting enzyme, influencing water intake.
Area of Science:
- Neuroscience
- Physiology
- Animal Science
Background:
- The role of the renin-angiotensin system in regulating thirst and sodium appetite is well-established.
- Investigating central mechanisms of thirst regulation in large animals like cattle is crucial for understanding species-specific physiological responses.
Purpose of the Study:
- To investigate the involvement of central angiotensin in mediating thirst and sodium appetite in cattle.
- To determine the site of action and potential formation pathway of brain angiotensin influencing fluid intake.
Main Methods:
- Intracerebroventricular (ICV) and intravenous infusions of angiotensin I, angiotensin-converting enzyme inhibitors (CEI), and angiotensin II antagonists were administered to normally hydrated and water-deprived cows.
- Water and sodium solution intake were monitored in response to these infusions.
- The lipophilicity of CEIs and their ability to cross the blood-brain barrier were considered.
Main Results:
- ICV angiotensin I stimulated water intake in sodium-deficient cows.
- ICV captopril (a CEI) blocked this response, while intravenous captopril affected sodium appetite.
- ICV ramipril (a lipophilic CEI) did not affect water intake but reduced sodium intake in dehydrated cows.
- An angiotensin II antagonist (Du Pont 753) administered ICV reduced water intake in dehydrated cows.
Conclusions:
- Central angiotensin, likely acting within the brain, is involved in regulating thirst in cattle.
- Brain angiotensin II may be synthesized via a pathway not involving converting enzyme and located within the blood-brain barrier, potentially in the median preoptic nucleus.