Influence of calcium antagonists on thrombin-induced calcium mobilization and platelet-vessel wall interactions

Platelet hyperactivity in hypertensive older patients is controlled by lowering blood pressure

OBJECTIVE

Patients with hypertension tend to have a high prevalence of atherothrombotic accidents. Platelet hyperactivity is frequently associated with hypertension. Because the vascular disease associated with hypertension evolves over the years, we investigated platelet activity parameters in a population of older hypertensive patients with no other risk factors for cardiovascular disease.

PARTICIPANTS

We studied 34 older, nonsmoking patients (mean age 74 +/- 5 years) with uncomplicated hypertension before and after the normalization of blood pressure (BP) was achieved with the angiotensin-converting enzyme inhibitor quinapril alone or in combination with the Ca2+ antagonist nifedipine.

MEASUREMENTS

Platelet aggregation, P-selectin (CD62) expression on the platelet surface, serum levels of Interleukin-1beta (IL-1beta) and of Interleukin-6 (IL-6), as well as plasma levels of soluble P-selectin and Endothelin-1 (ET-1), were analyzed.

RESULTS

All platelet hyperactivity parameters were reduced significantly with the normalization of BP at the end of antihypertensive drug treatment (systolic/diastolic: 186.2 +/- 2.7/103.4 +/- 1.1 mm Hg vs 135.0 +/- 1.3/85.9 +/- 1.9 mm Hg; P < .001). Those factors more strictly associated with endothelium injury, such as ET-1 and IL-6, did not show variations. A significant correlation (Spearman Rank test) was observed among all platelet function parameters and blood pressure values.

CONCLUSIONS

This study demonstrated that even in a population of older hypertensive patients with no other risk factor for atherogenic disease, normalization of blood pressure induces a significant reduction of the parameters of enhanced platelet hyperactivity independent of the action exerted, at the platelet level, by the antihypertensive drugs.

In vitro Effect of Verapamil on Platelet Activation Induced by ADP, Collagen or Thrombin

We studied the effects in Vitro of the calcium channel blocker verapamil (0.1, 0.2 or 0.3 mM) on platelet aggregation, on cytoplasmic Ca(+ +) levels and on TxB(2) production after activation of platelets with adenosine diphosphate (ADP) (100 µM), collagen (20 µg/ml) or thrombin (1 U/ml). A Platelet Ionized Calcium Aggregometer was used and washed, aequorin loaded platelets were employed. The drug was able to inhibit similarly and always significantly aggregation, Ca(+ +) fluxes and TxB(2) production when collagen was the agonist. Furthermore, inhibition of aggregation and TxB(2) production was significant at all the concentrations tested when platelets were activated by ADP or thrombin, but in this case inhibition of Ca (+ +) fluxes was observed only with the higher concentrations of the drug (0.2 or 0.3 mM). Hence, with these two last agonists inhibition of Ca(+ +) movements was less pronounced than inhibition of aggregation or TxB(2) production. These data suggest that platelet activation by collagen depends directly and almost exclusively on Ca(+ +) fluxes through biological membranes, while activation by ADP or thrombin is less strictly related to Ca(+ +) movements. Indeed, with these last two agonists verapamil may inhibit platelet activation also by calcium-independent mechanism(s).