Syneretic response to pressure in bovine and rhesus monkey vitreous

Excised bovine and rhesus monkey vitreous samples were subjected to different hydrostatic pressures (0.03, 1 and 2 atm) for 12 hr. At the end of the experiment the samples were frozen in a -70 degrees C dry ice-acetone bath and thereafter maintained in frozen conditions. Differential scanning calorimetry (DSC) was used to obtain freezable water (FW) content. The total water content of the samples was obtained by thermogravimetric (TGA) techniques. The non-freezable water (NFW) content was obtained as a difference between total and freezable water contents. The total water content did not show a trend in pressure dependence, neither in bovine nor in rhesus monkey vitreous samples. However, the free water/bound water ratio, i.e. FW/NFW, increased with increasing pressure in vitreous samples of both species. The trend of the average FW/NFW values as a function of hydrostatic pressure implies a simple syneretic response, i.e. the conversion of bound (non-freezable) water to free water as pressure was increased.