Blood volume regulation in dehydrated rodents: Plasma colloid osmotic pressure, total osmotic pressure and electrolytes

1. 1. Plasma colloid osmotic pressure of dehydrated Acomys cahirinus increased 26·8 per cent above value in normal A. cahirinus. In dehydrated Rattus norvegicus and Meriones crassus the colloid osmotic pressure decreased by 16·5 and 12 per cent respectively. 2. 2. The total osmotic pressure increased in all three species. 3. 3. The increase in total osmotic pressure of dehydrated R. norvegicus and M. crassus was due to the increase in electrolyte concentrations. No increase in sodium and chloride concentrations were measured in A. cahirinus. The increase in colloid osmotic pressure found in this mouse after dehydration was not large enough to explain the increase in total osmotic pressure. 4. 4. The role of plasma colloid osmotic pressure in blood volume regulation in the three species is discussed.