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Rats exhibit aldosterone-dependent sodium appetite during 24 h hindlimb unloading
Margaret J Sullivan1, Eileen M Hasser, Julia A Moffitt
1Department of Physiology, University of Missouri, Clumbia, MO, USA.
The Journal of Physiology
|March 30, 2004
Summary
Hindlimb unloading (HU), a model for microgravity, causes rats to decrease water intake but increase saline intake. Ingesting sodium during HU helps maintain plasma volume, driven by an aldosterone-dependent appetite.
Area of Science:
- Physiology
- Gravitational Biology
- Animal Models
Background:
- Hindlimb unloading (HU) simulates microgravity and bed rest effects.
- Understanding ingestive behavior's role in fluid balance during HU is crucial.
Purpose of the Study:
- To investigate how ingestive behaviors regulate body fluid balance during 24-hour HU.
- To determine the impact of saline availability on fluid intake and plasma volume during HU.
Main Methods:
- Rats underwent 24-hour hindlimb unloading.
- Fluid intake (water and saline solutions of 0.9% or 1.8% NaCl) was measured.
- Plasma volumes and hormone levels (aldosterone, renin activity) were analyzed.
- Spironolactone was used to block aldosterone's effects.
Main Results:
- Rats reduced water intake but increased saline intake during HU.
- Total fluid intake was maintained when saline was available.
- Plasma volume decreased with water-only intake but remained stable when 0.9% saline was available.
- Aldosterone levels increased, while renin activity did not, during HU.
- Spironolactone blocked the increased intake of 1.8% saline during HU.
Conclusions:
- Hindlimb unloading induces an aldosterone-dependent sodium appetite.
- Sodium ingestion during HU is critical for maintaining plasma volume.
- Ingestive behavior, specifically sodium appetite, plays a key role in fluid homeostasis during simulated microgravity.