Does increased platelet release normalize during anti-hypertensive treatment?

Blood platelet function was evaluated in 10 men, all 50 years old, with untreated, mild hypertension. Each patient was examined four times: At the beginning of the study, after 5 weeks on placebo treatment, after the following 5 weeks on propranolol 160 mg daily, and finally after a second period of 5 weeks on placebo. At baseline the plasma level of the platelet release product beta-thromboglobulin (BTG) was 41.6 (30.5-57.0) micrograms/l (median and 95% confidence interval). During the first placebo period BTG was normalized to 21.0 (14.1-25.9) micrograms/l. While systolic blood pressure and heart rate fell during beta-adrenergic receptor blockade, BTG remained unchanged throughout the rest of the observation periods. Platelet size increased significantly during treatment with beta-blocker. The present study indicates that the normalization of elevated platelet function which previously has been reported to occur during anti-hypertensive drug therapy, may be explained by patient adaptation to the blood sampling procedure.