Effects of dehydration and rehydration on the intravascular space in horses.

This research investigates the impact of dehydration and rehydration on the blood circulation system of horses from sub-tropical and desert climates, through experiments on changes in red cell parameters and plasma protein concentration during a period of 72 hours of dehydration and 24 hours of rehydration.

Dehydration and Rehydration Process

• The study focuses on understanding changes within the intravascular space of horses under a period of 72 hours of dehydration and a subsequent 24 hours of rehydration. The intravascular space refers to the space within the blood vessels.
• The experiments involve sub-tropical horses and desert-dwelling horses, which have presumably adapted to withstand significant periods of dehydration. These animals were subjected to dehydration by withholding water for 72 hours, followed by a rehydration period of 24 hours.

Observations during Dehydration

• Findings showed that the red cell count, the hemoglobin levels, and the hematocrit or the volume percentage of red cells in blood, increased during the initial 48 hours of dehydration.
• Beyond 48 hours up to the 72nd hour of dehydration, these values decreased, indicating a fluid shift from the interstitium/hindgut (spaces between cells and intestines respectively) into the blood vessels, likely as an adaptive response to dehydration.

Observations during Rehydration

• The research then observes recovery following the hydration period. By the end of 24 hours of rehydration, most of the parameters of the horses’ intravascular space had returned to baseline values.
• Therefore, it suggests that these species of horses can recover fairly swiftly from significant periods of dehydration once they have access to water.

Differential Effects and Defence Mechanisms

• The study also highlights certain aspects such as the mean cell volume, mean cell hemoglobin, mean cell hemoglobin concentration, and total plasma protein, which were not significantly different between the two breeds or during different stages of hydration.
• This implies that not all components of the intravascular space are affected by dehydration and rehydration periods in the same way. Certain factors like albumin levels were maintained, which may help preserve plasma volume under such conditions.
• Additionally, red blood cells showed significant resilience, temporarily undergoing dehydration and overhydration but resisting osmolysis, the breakdown of the cell wall due to imbalance in water concentration.