Mobilised fluid volumes after induced hyperosmolality in the rat

Hyperosmolar infusions of the inert pentose sugar, xylose (MW 150), were used to induce hyperosmolar states in non-starved and starved rats. Using 51Cr EDTA and RIHSA the extracellular fluid (ECF) and plasma fluid volumes (PV) were determined before and after infusions. The cause of weight loss after 24-30 h starvation was also examined. Equal osmolar provocation in starved and non-starved animals caused the same degree of hyperosmolality. The greater the osmolality increase the larger the volume of intracellular fluid mobilised. Despite the total ECF volume increments being large relative to PV, this fluid compartment remained hardly effected by the fluid released from the cells. No evidence could be found to support 24-30 h starvation as causing a measurable fluid balance defect, a finding of considerable importance when considering short term problems arising out of starvation. The strict control of PV in normovolemic rats has again been confirmed.