multiple sclerosis functional roles and therapeutic targeting autoimmunity 2007 march 40 2 148 160 to test whether int131 is able to penetrate the intact bbb int131 was radiolabeled with tritium u201c 3 h int131 u201d prior to intraperitoneal injection into adult sprague dawley rats the purity of the radiolabeled int131 was determined by high performance liquid chromatography hplc fractionation prior to injection and again at the close of the experiment at both time points virtually all of the radiolabeled material was found in a single peak demonstrating the stability of 3 h int131 over the course of the study at the time of injection into the test animals the labeled int131 was mixed with non labeled int131 such that the injection of 50 mg kg of int131 resulted in each animal receiving 1000 u03bcci kg of labeled drug the test animals were sacrificed at 1 6 and 24 hours after injection and blood brain cerebrospinal fluid u201c csf u201d spinal cord kidney liver and small bowel were harvested for determination of 3 h int131 content by liquid scintillography table 1 lists the int131 concentration in all the tissues analyzed one hour after a single administration of u02dc 50 mg kg of 3 h int131 the average amount.