Fluid compartmentation in skeletal muscle and carcass of Mus musculus acclimated to water scarcity.

1. Total water (TW), and extracellular water (ECW) (as sodium and chloride space) were determined in skeletal muscle and carcass of Mus musculus acclimated to long-term water shortage. 2. The presence of fat in control mice and those in early stages of acclimation resulted in an apparent increase in TW and ECW as acclimation proceeded. 3. In contrast, fluid volumes per fat-free weight were either unchanged from controls or reduced. 4. Sodium space exceeded chloride space. 5. Muscle and carcass had essentially the same pattern of fluid shifts. 6. We conclude that ECW maintenance is a preeminent component of the acclimation process in this species.