Role of Erythrocyte in Blood Iodine Transport Using Radioiodine I131

Abstract

Rats were sacrificed at time intervals of 15 min. to 24 hrs. and the amt. of radioiodine I131 in the circulating whole blood volume, the plasma and the erythrocyte fractions were made for each period. The whole blood percentage activity of the injected I131 declined from 19.6% at 15 min. to 0.46% at 24 hrs. The plasma declined from 12.52% at 15 min. to 0.34% at 24 hrs., and the erythrocytes from 6.15% at 15 min. to 0.12% at 24 hrs. This loss from the blood was considered to represent the thyroid uptake, kidney excretion and the dispersion into the body fluid compartments. The percentage of whole blood radioactivity retained by the erythrocytes was found to be nearly constant over the 24 hr. period, from 36.2% of the whole blood radioiodine at 15 min. to 35.9%. at 24 hrs., indicating that loss of radioiodine from the whole blood was quickly adjusted between the erythrocyte and the plasma. When the percentage of whole blood radioiodine in the erythrocyte was compared with the estimated percentage of whole blood water in the erythrocyte, the ratio was nearly equal for the first 2-6 hrs., and declined at 24 hrs. to 0.87.