Disposition of human fibrinopeptide A in normal and nephrectomized rabbits

The distribution, elimination, and metabolism of human fibrinopeptide A (FPA) were studied in normal and nephrectomized rabbits. The activity of 125-I-labeled desamino-tyrosyl human FPA (DAT-FPA) was followed over 4 hours after i.v. administration. Results show that in normal rabbits (n = 10) DAT-FPA is eliminated from plasma in four phases with half-lives of 30 sec, 3.5 min, 15 min, and 90 min. The distribution of 123-I-labeled DAT-FPA in plasma was determined in 15 control rabbits with scintigraphy over 2 hours. DAT-FPA was distributed primarily in the cardiovascular system, liver, and kidneys. In some animals minimal radioactivity was detected over the gall bladder. Radioactivity accumulated rapidly in the urinary bladder, approximately 50% being recorded after 15 min and 90% after 120 min. In the heart area radioactivity decreased with half-lives of 25 sec, 7.5 min, 25 min, and 180 min. Nephrectomized rabbits had similar initial fast distribution of DAT-FPA after administration of 125-I-labeled (n = 10) and 123-I-labeled peptide (n = 10). The estimated half-life of the slow component was in the order of several hours. The results of the scintigraphic and gel chromatographic studies show that FPA is primarily excreted in the urine. Previously reported half-lives of FPA reflect distribution rather than steady state conditions.