title: The "critical colloid dose" in studies of reticuloendothelial function.
abstract: The [99mTc]sulfur colloid distribution in rat organs was investigated after the administration of different amounts of colloid particles. Saturation of the liver and spleen was not observed. Blood clearance was significantly reduced 15 min after injection above approximately 3 X 10(9) particles per kg body weight. With an increasing number of injected particles, lung uptake increased and bone marrow uptake decreased. Microfiltration studies showed that the colloid is unaffected by dilution with saline but may be affected after incubation in normal rat plasma. We conclude that the distribution of [99Tc]sulfur colloid in organs varies with the number of injected particles and therefore, is not dependent upon the blood flow to the reticuloendothelial organs alone. The "critical colloid dose" may differ among the reticuloendothelial organs and cannot, therefore, be evaluated by blood clearance measurements alone. The considerable influence of the number of injected colloid particles on bone marrow uptake should also be recognized when carrying out dosimetric calculations.
mesh_terms: D000818:Animals; D008297:Male; D012157:Mononuclear Phagocyte System / Q000000981:diagnostic imaging* / Q000502:physiology; D010316:Particle Size; D011877:Radionuclide Imaging; D051381:Rats; D013671:Technetium Tc 99m Sulfur Colloid / Q000008:administration & dosage / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D013671:Technetium Tc 99m Sulfur Colloid