PubMed1986
We have evolved from the sea, are composed mostly of water, the medium and solvent wherein most vital processes occur, and phylogenetically and ontogenetically lose water continually as we age. An embryo is about 90% water, a newborn child about 80% water, a mature adult about 70% water, an older adult about 60% water with recent work indicating that in senescence the percentage of body water is actually below 60%. The mechanisms of the water loss in aging have not been elucidated. From a theoretical point of view, there is good reason to believe that there may be profound changes in the chemical potential of intracellular and interstitial water with age due to increased macromolecular interaction or aggregation from cross linking, polymerization, insolubility, etc.; all of which are known to increase with aging. The resultant increased macromolecular solute-solute interaction would be accompanied by decreased macromolecular solute-solvent interaction, thereby causing a higher solvent (water) chemical potential. This would facilitate the loss of bound water, thereby explaining the observed losses in body water with age. The ocular lens is a microcosm of aging, in that from its nucleus to cortex, the oldest to youngest cells are concentrically arranged, as in a tree. We have developed a method to directly measure lens tissue oncotic pressure in an attempt to experimentally test the above cited hypothesis.