A STUDY WITH RADIOACTIVE ISOTOPES OF THE PERMEABILITY OF THE BLOOD-CEREBROSPINAL FLUID BARRIER TO IONS

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Abstract
The developments in the prep, of induced radioactive isotopes by means of the cyclotron offer a hitherto unavailable method of studying the blood-cerebrospinal fluid barrier function with respect to the normal ion constituents of the body labeled with their radioactive isotopes. Permeability studies were carried out on dogs with the cations of Na, K, Rb and Sr, and the anions bromide, iodide and phosphate. Detns. were made of the rates of the disappearance of the intraven. injected ions from the circulating blood plasma, and the rates of their accumulation in freshly formed cerebrospinal fluid. Similar curves were obtained for the disappearance of all the injected ions from the blood plasma, although there were great differences in rates. Calculation of the vol. of distribution of the different ions indicated that Na and bromide became uniformly distributed throughout the extra-cellular fluids of the body. K and Rb accumulated mainly in the intracellular phase of the soft tissues of the body. Phosphate and Sr were largely taken up by the skeleton. The rate of increase in cone, of the labeled-ions in the cerebrospinal fluid followed the order K > Na > bromide > Rb > Sr > phosphate > iodide. The spinal fluid concs. curves of K, Rb, and phosphate exhibited pronounced maxima at about 20, 30 and 60 mins., respectively. Sr exhibited a less pronounced maximum and Na no maximum in the spinal fluid conc, curve. The hindrance to the free passage of ions from the blood stream to the extracellular fluid of the C.N.S. and the deviation from the Donnan law of distribution of the steady ratios of the concs. of these ions between the cerebrospinal fluid and the plasma constitute evidence that the exchange between the blood and brain takes place by a process of secretion and not by simple diffusion or ultrafiltration.

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