STUDY OF PLATELET-ADHESION IN PATIENTS WITH UNCOMPLICATED HYPERTENSION

Objective To evaluate platelet function in patients with essential hyp ertension by sensitive methods investigating platelet adhesion and exp ression of some platelet glycoproteins (GP), namely GPIIb/IIIa (CD41/a lpha(2) beta(3)) and GMP-140 (CD62/P-selectin/PADGEM). Other markers o f platelet (beta-thromboglobulin) and endothelium activation (von Will ebrand factor) were also measured. Methods We studied 21 uncomplicated essential hypertensive patients and 20 healthy normotensive control s ubjects, non-smokers, matched for age and sex. Resting and stimulated platelet adhesion was performed with a colorimetric method using the a ctivity of platelet acid phosphatase for the determination of the numb er of platelets adhering to human plasma- or fibrinogen-coated microwe lls. Platelet activation was characterized by flow cytometric measurem ent of GPIIb/IIIa and GMP-140 in whole blood and washed platelets susp ensions, with antihuman fluorescent monoclonal antibodies. Results Thr ombin-stimulated platelet adhesion to human plasma-coated microwells w as significantly higher in hypertensive patients than in control subje cts (0.05 U/ml thrombin: 13.4 +/- 1.0 versus 7.7 +/- 0.6% adhesion; 0. 1 U/ml thrombin: 19.4 +/- 2.3 versus 12.6 +/- 1.8%; means +/- SEM), wh ereas platelet adhesion to fibrinogen-coated wells did not differ in t he two groups. Flow-cytometry analysis of whole blood demonstrated a s ignificantly increased expression of GMP-140 in hypertensive patients compared with normal subjects (percentage of CD62(+) platelets: 7.3 +/ - 1.2 versus 3.7 +/- 1; means +/- SEM), whereas the expression of GPII b/IIIa did not differ in the two groups (percentage of CD41a(+) platel ets: 72.5 +/- 4.5 versus 70.4 +/- 3.9). Moreover, flow cytometry showe d an increased size of platelets in hypertensive patients compared wit h that in control subjects (forwards scattering: 46.5 +/- 1.5 versus 3 8.9 +/- 1.1; means +/- SEM). Flow-cytometric evaluation of washed plat elet suspensions showed no statistically significant differences betwe en the expression of GMP-140 and GPIIb/IIIa in the two groups. beta-Th romboglobulin plasma levels were higher in hypertensive patients than they were in normal subjects (36.3 +/- 2.0 versus 28.2 +/- 1.3 ng/ml; means +/- SEM). Von Willebrand factor plasma levels were not significa ntly different in the two groups (101.2 +/- 10.3 versus 86.3 +/- 5.6 U /dl). Conclusions These findings provide further evidence that there i s a significant, albeit weak, platelet activation in hypertensive pati ents compared with normal subjects.