Intracranial pressure may be strikingly changed by varying the osmotic pressure of the blood. The intravenous or intraperitoneal injection of hypertonic dextrose, urea or sodium chloride1 may lower the intracranial pressure from normal to levels well below atmospheric pressure.2 In this paper we have studied the effects of such hypertonic solutions upon the diameter of the pial arteries and veins during the typical intracranial pressure response. In each of the six animals examined very definite constriction of these vessels occurred at the height of the response.
Many organs contribute in the transfer of fluids from the tissues into the blood after the injection of hypertonic solution, although some contribute more than others. It is known that the brain and cerebrospinal fluid are greatly reduced in volume.3 Moreover, associated with shrinkage of the tissue, there may be alteration in function, especially in smooth muscle. Hughson and Scarff4