Further studies on the nature of fluid compartmentalization in chick calvaria

Labeled mannitol and polyethylene glycol (mol. wt. 4000), PEG, were used as space markers to estimate the fluid compartmentalization of calvaria taken from 3-5-day-old chicks. The mannitol results indicated that about 80% of the water in these bones is extracellular. Only a small fraction of this extracellular space was available to the diffusion of polyehtylene glycol. Adsorption studies in vitro and prior incubation of the tissues with hydrolytic enzymes indicated that the phenomenon of exclusion of PEG was primarily physical in nature. The polyethylene polymer is excluded from the water of hydration of the mineral phase. Apparently much of the extracellular water (two-thirds) of bone is in the form of crystal hydration.