IODINATED PARTICLES IN THE RAT THYROID I. A RAPID SEPARATION METHOD

ABSTRACT In a first step, the quantitative preparation of the whole population of iodinated particles was reinvestigated in thyroids obtained from rats maintained in an isotopic equilibrium with 125I. The maximum yield in the iodinated particles was obtained for a 0.15 m sucrose solution in 0.1 m Tris-HCl buffer pH 7. This yield was 3.5 % and 1.7 % of the total iodine content of the thyroid for rats adapted to receive 50 (group 50) and 5 μg (group 5) of iodine daily respectively. The iodinated particles of group 50 were found to be more sensitive to pH variations than those of group 5. In a second step, a rapid method was developed to separate the whole population of iodinated particles into physiological populations (tentatively colloid droplets and secondary lysosomes). By centrifuging onto a discontinuous Ficoll gradient, three distinct iodine peaks were regularly obtained for rats of group 5 and 50 and also for other rats receiving a diet rich in iodine. For group 50, the iodine pools (127I) as measured by isotopic equilibrium were found to represent about 16% (peak 1), 25 % (peak 2) and 59 % (peak 3) of the total particulate iodine content of the gland. The possible nature of these three populations of iodinated particles is discussed.