Smoking further increases platelet activity in patients with mild hypertension.

In this study the authors examine whether smoking further heightens platelet activity and reduces fibrinolysis above that already present in mild hypertension. Ten smokers and 11 non-smokers, all with mild hypertension (defined as a diastolic pressure between 90 and 110 mm Hg) were compared for their platelet activity in vitro and in vivo and for their fibrinolytic activity. Successive measurements were made with the patients lying at rest after they had assumed the erect posture for 10 min and at the end of a 5-min moderately strenuous exercise test. The threshold for platelet aggregation by ADP in vitro was significantly lower in samples taken from the smokers at rest (1.4 +/- 0.9 mu mol L(-1)) than in the non-smokers (3.5 +/- 2.5 mu mol L(-1)), and the difference persisted both in the upright posture and after exercise. The level of platelet release of beta-thromboglobulin was, likewise, higher in the smokers in the upright posture. Neither standing up nor physical exercise had any significant influence on either of these two indices of platelet activity. The euglobulin clot lysis time was slightly longer in the smokers than in the non-smokers in all three experimental situations, but the differences were not significant. Inhibitor of tissue plasminogen activator was not materially different in the two groups (Table 2). The results indicate that smoking adds a further element of heightened platelet activity to that inherently present in hypertension.