Effect of spirapril and hydrochlorothiazide on platelet function and euglobulin clot lysis time in patients with mild hypertension.

Thirteen patients with mild hypertension (untreated diastolic blood pressure of 95 to 114 mmHg) received, in random order, three successive treatments of four weeks with placebo, spirapril (6 mg daily), or hydrochlorothiazide (HCT2) (24 mg daily). At the end of each treatment, blood samples for assessment of platelet aggregation and platelet release of platelet factor 4 (PF4) and for assessment of fibrinolysis, estimated by tissue plasminogen activator (t-PA), plasminogen activator inhibitor-type 1 (PAI-1), and euglobulin clot lysis time (ECLT), were taken, first at rest, then immediately after five to ten minutes of vigorous exercise, and finally after the subsequent hour of recovery rest. Platelet aggregation induced in vitro by adrenaline significantly decreased during treatment with HCT2, the threshold rising to 10 microM as compared with 1.0 with placebo (P < 0.05) at rest, and the threshold for adenosine diphosphate (ADP) aggregation also rose, from 2 microM to 4 (NS). The resting plasma PF4 value fell, although not significantly, during HCT2 treatment from the placebo value of 3.28 to 2.56 ng/mL. During spirapril treatment there was no change in the threshold of either adrenaline or ADP for aggregation of platelets sampled at rest, and the PF4 plasma levels showed no significant reductions at rest. However, during exercise PF4 showed an approximate doubling of the resting value irrespective of therapy. This exercise-induced increase in PF4 was significantly reduced by spirapril as compared with placebo (P < 0.05). ECLT and t-PA did not shift significantly from the placebo level during either therapy. PAI-1 did not change during spirapril therapy, but during HCT2 treatment it fell, although not significantly, to 9.36 IU/mL from 15.91 with placebo (NS). Spirapril and HCT2 did not produce any unwanted side effect on platelet function or fibrinolysis. HCT2 seems to decrease platelet activity at rest, whereas spirapril seems to some extent to decrease platelet activity at exercise.