Determination of tissue plasminogen activator in plasma samples by means of a radioimmunoassay

A solid phase double antibody radioimmunoassay for measuring tissue plasminogen activator (t-PA) in human plasma is described using purified human melanoma cell t-PA and specific goat anti-t-PA IgG. The concentration of t-PA antigen in citrated human plasma sampled at rest was 4.4 +/- 1.3 micrograms/l (mean +/- SD) for healthy individuals (n = 20). After 10 min of venous occlusion the level of t-PA antigen was increased to 13.9 +/- 6.2 micrograms/l. The accuracy was monitored by recovery experiments using plasma from nine healthy individuals and nine patients to which was added low (5 micrograms/l) and high (25 micrograms/l) levels of purified t-PA. The detection limit of the method was estimated as 0.08 micrograms/l. An excellent correlation was found on comparing the t-PA antigen increase with the t-PA activity increase obtained during venous occlusion. In plasma collected prior to venous stasis, the total concentration of detectable t-PA antigen is found mainly in an inactive form. In contrast the t-PA antigen released upon venous occlusion seems to be largely in an active form.