EFFECT OF PROPRANOLOL (LONG-ACTING) ON THE CIRCADIAN FLUCTUATION OF TISSUE-PLASMINOGEN ACTIVATOR AND PLASMINOGEN-ACTIVATOR INHIBITOR-1

The incidence of myocardial infarction and sudden cardiac death is highest in the morning. Inhibition of fibrinolytic activity in blood also peaks in the morning and this inhibition may favor the development of arterial thrombosis. It has been reported that patients treated with beta-blockers do not show the typical circadian pattern of onset of myocardial infarction and sudden cardiac death. This study was undertaken to investigate whether beta-blockade alters the circadian rhythm of 2 major fibrinolytic factors, tissue-plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1). Repeated blood samples were taken over a 24-hour period in 13 healthy volunteers: 7 taking 160 mg/day of long-acting propranolol orally for 14 days, and the other 6 taking no medications. Blood samples were analyzed for the plasma levels of t-PA activity, t-PA antigen, PAI activity and PAI-1 antigen. A significant circadian variation of all 4 parameters was present in both groups. No significant differences in peak and nadir values, 24-hour mean, amplitude of fluctuation, and time of peak and nadir were found between the treated and untreated subjects. The data therefore suggest that propranolol treatment does not affect the plasma concentrations at rest or the endogenous circadian rhythm of t-PA and PAI-1 in healthy volunteers. The reported alteration in the circadian pattern of onset of myocardial infarction and sudden cardiac death by beta-blockers does not appear to be mediated by effects on the fibrinolytic system.