title: Daytime fluctuations in blood of tissue-type plasminogen activator (t-PA) and its fast-acting inhibitor (PAI-1).
abstract: Circadian fluctuation in blood fibrinolytic activity was studied in 10 volunteers in the day-time period at 09.00, 12.00 and 15.00 h. Activity of tissue-type plasminogen activator (t-PA) was found to increase from 09.00 to 15.00 h in accordance with known results with global assays of blood activity. Also, activity and antigen of plasminogen activator inhibitor 1 (PAI-1) and antigen of t-PA showed fluctuations but with an opposite pattern to that of t-PA activity, with highest levels in the morning and lowest ones in the afternoon. Activity of a reversible t-PA inhibitor was constant. The discordance between fluctuations in antigen and in activity of t-PA is attributed to the inhibitory effect of PAI-1 on t-PA activity. It is concluded that the appearance into the blood of t-PA and PAI-1 shows a daytime fluctuation with a similar pattern, suggesting a co-ordinated circadian fluctuation in production of both proteins by endothelial cells.
mesh_terms: D000328:Adult; D000941:Antigens / Q000032:analysis; D002940:Circadian Rhythm; D006023:Glycoproteins / Q000097:blood* / Q000276:immunology; D006801:Humans; D008297:Male; D010960:Plasminogen Activators / Q000037:antagonists & inhibitors*; D015849:Plasminogen Inactivators; D010959:Tissue Plasminogen Activator / Q000097:blood* / Q000276:immunology
chemical_list: D000941:Antigens; D006023:Glycoproteins; D015849:Plasminogen Inactivators; D010960:Plasminogen Activators; D010959:Tissue Plasminogen Activator