History and Objectives: Water content (WC) elevation of brain tissue has a direct relationship with the brain edema and determination of the water content of brain is very important. Since the alternation in WC of brain is related to the changes in the specific gravity (SG), the present investigation is carried out in order to determine SG of rat brain hemispheres at normal state and edema in order to obtain its relationship with brain water content.

Materials and Methods: An experimental study was conducted and with the aid of MARMAROU method proper location is determined. A column of fluid from various layers with different SG values was obtained with the aid of paraffin and bromobenzene. Relationship between SGs and height of the column was determined. Brain tissue of rat was divided into two groups of control and experimental. Carotid arteries were closed in the experimental group for 30 minutes. Water content at both brain hemispheres in both groups by classic drying of tissue were measured and with the use fluid column, the specific gravity of each sample was determined. Relationship between SG and WC was assessed. A group of 10 rats were selected and their carotid arteries were blocked for 15 minutes in order to examine this relationship. 2 methods of drying and relationship between SG and WC were used to determine the water content and compared.

Results: There was a significant difference in the WC and SG of brain tissue in both hemisphere in control and experimental groups (P<0.05). A linear relationship between SG and WC both brain hemisphere (r²=0.99) and SG dry tissue and SG of brain on both hemisphere was obtained. Assessment of relationship of SG and WC shows that significant difference in WC determined by classic dry method and WC calculated from SG values does not exist.

Conclusion: With the use of paraffin and bromobenzene and creation of fluid column, a significant difference between height of column and SG exists and shows that this fluid is suitable for SG determination. There is a difference between WC and SG in two brain hemispheres. Further study is needed to investigate that underlying cause of this difference. In addition, each component of a given hemisphere ought to be studied.