Hypertension and brain oedema: an experimental study on acute and chronic hypertension in the rat.

To determine under what circumstances hypertension is associated with brain oedema, the specific gravity of the brain was measured in acutely hypertensive, renal hypertensive and spontaneously hypertensive rats. Maximum mean arterial pressure (MAP) in acute hypertension induced by intravenous amphetamine or bicuculline was 171 +/- 5 and 181 +/- 5 mmHg respectively. In spite of pronounced extravasation of Evans blue-albumin, there was no decrease in specific gravity except in the diencephalon in rats given bicuculline (p less than 0.05). Cortical and cerebellar samples from renal hypertensive rats (MAP 174 +/- 14 mmHg) were lighter than corresponding regions in normotensive rats (p less than 0.001) although the brains showed little or no macroscopic extravasation of Evans blue-albumin. Neither macroscopic protein leakage nor increase in water content was observed in brains from spontaneously hypertensive rats (MAP 210 +/- 5 mmHg). It is concluded that renal hypertension is more likely to lead to brain oedema than spontaneous genetic hypertension or acute hypertension.