Studies on tumor necrosis factor (TNF)- I. Pharmacokinetics of human recombinant TNF in rabbits and monkeys after intravenous administration

1. 1. By intravenous (bolus) administration of human recombinant tumor necrosis factor (2.5 × 106 units) into rabbits and monkeys it has been possible to follow its decay in the plasma and to determine the pharmacokinetic parameters. 2. 2. After labelling TNF with 125I, simultaneous determination of protein-bound radioactivity and bioactivity was carried out with the result that radioactivity decays somewhat slower than bio-activity suggesting that the use of the former tracer alone may underestimate TNF catabolism. 3. 3. Simultaneous determination of 125I-TNF in rabbit plasma and lymph after intravenous and subcutaneous administration indicated a lymph to plasma TNF concentration ratio of about 0.1 and 1 or more for the two routes, respectively.