Abstract
In order to clarify the causative mechanism of ischemic brain edema, having prepared an experimental model with a Mongolian gerbil in whose brain an ischemic area can be easily produced by a unilateral carotid artery ligation (ULCL), the author made a series of periodic examinations on the brain water contents, brain tissue Na+ and K+, brain energy metabolism (ATP, c-AMP and lactate), CBF and 131I-RISA uptake into the brain tissue respectively. From the viewpoint that edematous fluid is to be produced either by blood or by spinal fluid, brain edemas were classified into the one due to blood-brain barrier and the other due to spinal fluid brain barrier. Then the former group was further classified into two groups. the one due to functional and the other due to organic disorders, and the following results were obtained.
1) Observations of the brain water contents after ULCL proved that an ischemic brain edema occurs as early as within two to three hours after an ischemia.
2) Shortly after the ligation, a significant increase of Na + and decrease of K+ in the brain tissue were observed. It is considered hat these electrolyte changes may suggest the occurrence of the functional disorder of the blood-brain barrier by sodium pump disfunction.
3) After the ligation, along with the CBF decrease, a significant decrease of ATP, and increase of lactate, and a temporary increase of c-AMP in the brain tissue were observed. This shows that the functional disorder of blood- brain barrier caused by the disturbance of brain energy metabolism occurs and this is accompanied by the osmotic pressure within the brain tissue, and qualitative changes of membrane, etc. It was assumed that brain edema occurs shortly after ischemia.
4) Within 12 hours or so following the ligation, a tendency could be recognized that 131I RISA began to leak out into the brain tissue. It suggests that the organic disorder of the blood-brain barrier was occurred, it was assumed that the brain edema caused shortly after the ischemia could be further developed by this organic disorder.
5) Judging from the above results, it can be concluded that the mechanism of ischemic brain edema is due to the functional disorder of the blood-brain barrier caused by the disturbance of brain energy metabolism. In addition to this, the brain edema due to the organic disorder of the blood-brain barrier is occurred within 12 hours or so following the ischemia.
