Factors influencing the concentration gradient of protein in cerebrospinal fluid.

The concentration of protein in the cerebrospinal fluid (CSF) is about 0.5 per cent that of plasma. This difference in concentration is generally considered (1) to be dependent upon the blood-CSF barrier. The normal concentration gradient of protein from a low level in the ventricles, 6 to 15 mg. per cent, to an intermediate level in the cisterna magna, 15 to 25 mg. per cent, to the highest level in the lumbar sac, 20 to 45 mg. per cent (2), has not been satisfactorily explained. To study the nature of this gradient, two groups of experiments were performed, determining: 1) the exchange of radioiodinated serum albumin (RISA@) between the plasma and the various levels in the CSF, and 2) the relative concentration of the albumin, globulin and "prealbumin" constituents at these levels, employing zone electrophoretic analysis. In previous investigations in the dog (3), it has been shown that the plasma albumin exchanges rapidly with the protein in the CSF. Following intravenous injection, RISA® appeared in the cisternal fluid within 20 minutes, reached a maximum at about 20 hours, and subsequently disappeared at a slower rate than in the plasma. In the present study, RISA® was administered intravenously to infants with communicating hydrocephalus to determine if differences in the rates of RISA® appearance exist at different sites along the neuraxis. The demonstration of such rate differences could then be interpreted to indicate nonuniformity of the blood-CSF barrier to protein at these different levels. Similarly, the concentration of albumin in CSF would be expected to be