Summary
Tissue plasminogen activator (tPA) activity in blood and blood plasma has been difficult
to determine because it is unstable, especially in subjects with high levels of plasminogen
activator inhibitor type 1 (PAI-1). We have attempted to stabilize the tPA activity
by collecting 9 volumes of blood in 1 volume acidic citrate buffer which immediately
lowers the pH of the blood. At final blood pH of 4.9 to 6.3, consistent and high tPA
activity levels were found. One acidic citrate buffer composition, 0.5 mol/1 citrate
buffer pH 4.0, resulted in final blood pH 5.5, tPA half-life of 10 days and an acceptably
low degree of haemolysis. This anticoagulant composition was selected for more extensive
evaluation and was used to collect blood plasma samples from 29 volunteers in the
morning after a 10-minute bed rest. Basal tPA activity, mean and SD, was 0.47 ±0.21
IU/ml. After donating of the first blood sample, 10 of the volunteers entered into
a 24-hour fast after which they donated a second sample. During the fast, the basal
tPA activity increased from 0.34 ±0.21 to 0.47 ±0.23 IU/ml (p = 0.05) and the PAI-1
activity decreased from 11.4±11.6 to 6.3±8.9 U/ml (p = 0.04).
Keywords
Tissue plasminogen activator - tPA - tPA activity - Basal tPA activity - Blood sample
collection - Citrate buffer - Diet experiment
