title: Partition of 125I-iodoantipyrine among erythrocytes, plasma, and renal cortex in the dog.
abstract: The tissue/blood partition coefficient, lambda tb, defined as the amount of blood having the same tracer content as one unit of tissue at diffusion equilibrium, was determined for 125I-iodoantipyrine (I-Ap) and tritiated water (THO) in the dog kidney cortex. Measurements were made after in vivo equilibration for 75 to 300 s and with liver circulation excluded. In 18 kidneys, lambda tb for I-Ap averaged 1.38 (S.D. 0.13) w/w (weight/weight), without significant correlation to hematocrit (range: 23-43) or to urine pH (range 5.5-8.6). The lambda tb for THO averaged 0.97 (S.D. 0.06) v/w (volume/weight), close to the relative water contents. Erythrocyte/plasma partition for I-Ap was 0.82 w/w, compared to a water partition of 0.72. Thus, at diffusion equilibrium the apparent I-Ap concentration in renal cortical and red cell water exceeds that of plasma water by 14 and 60%, respectively. It follows that I-Ap cannot be used as a general indicator for total tissue water content. When used for measurement of local blood flow and modum Kety, lambda tb must be determined for each tissue and species.
mesh_terms: D000818:Animals; D000983:Antipyrine / Q000031:analogs & derivatives* / Q000378:metabolism; D001834:Body Water / Q000378:metabolism*; D004285:Dogs; D004912:Erythrocytes / Q000378:metabolism*; D007457:Iodine Radioisotopes; D007672:Kidney Cortex / Q000098:blood supply* / Q000378:metabolism; D007679:Kidney Medulla / Q000098:blood supply / Q000378:metabolism; D010949:Plasma / Q000378:metabolism; D012039:Regional Blood Flow; D014316:Tritium
chemical_list: D007457:Iodine Radioisotopes; D014316:Tritium; D000983:Antipyrine; C008135:iodoantipyrine