Dose-dependent effects of verapamil and nifedipine on in vivo platelet function in normal volunteers

Potential Protective Role of Blood Pressure-Lowering Drugs on the Balance between Hemostasis and Fibrinolysis in Hypertensive Patients at Rest and During Exercise

In patients with hypertension, the triad represented by endothelial dysfunction, platelet hyperactivity, and altered fibrinolytic function disturbs the equilibrium between hemostasis and fibrinolysis and translates into a hypercoagulable state, which underlies the risk of thrombotic complications. This article reviews the scientific evidence regarding some biological effects of antihypertensive drugs, which can protect patients from the adverse consequences of hypertensive disease, improving endothelial function, enhancing antioxidant activity, and restoring equilibrium between hemostatic and fibrinolytic factors. These protective effects appear not to be mediated through blood pressure reduction and are not shared by all molecules of the same pharmacological class.

Different effects of calcium antagonists, nitrates, and beta-blockers on platelet function. Possible importance for the treatment of unstable angina

BACKGROUND

The three major classes of antianginal drug all inhibit platelet aggregation at high concentrations in vitro, but detecting clinically relevant effects has proved to be more difficult. We used whole-blood flow cytometry, a sensitive method that allows direct measurement of activation antigens on the surface of individual platelets in whole unfixed blood, to evaluate the effect of representative antianginal drugs on platelet function in vivo in healthy volunteers.

METHODS AND RESULTS

The effects of glyceryl trinitrate (GTN), amlodipine, and atenolol were studied in nine normal volunteers. Fibrinogen binding to activated GP IIb/IIIa and expression of P-selectin, GP Ib, and GP IIb/IIIa on the platelet surface were measured. In addition, fibrinogen binding and P-selectin expression were measured in response to ex vivo stimulation with the agonists ADP and thrombin. The three drugs had very different effects on platelets. GTN inhibited platelet fibrinogen binding and expression of P-selectin at rest and in response to agonist stimulation, whereas amlodipine enhanced P-selectin expression and atenolol increased fibrinogen binding in response to agonists. Atenolol did not block the stimulatory effects of epinephrine on ADP-induced platelet activation. GTN neutralized the proactivatory effects of amlodipine, whereas the effects of atenolol and amlodipine were not additive.

CONCLUSIONS

The three main classes of antianginal medication have different and possible clinically relevant effects on platelet behavior in vivo, nitrates causing inhibition of aggregation (fibrinogen binding) and degranulation (P-selectin expression), calcium antagonists enhancing degranulation, and beta-blockers enhancing aggregation.

Stress-induced hemodynamic and hemostatic changes in patients with systemic hypertension: effect of verapamil

Stress-induced hemodynamic and hemostatic responses may acutely trigger atherosclerotic plaque disruption and thrombosis leading to myocardial infarction. This study was designed to evaluate the responses to three stressors and to determine if once-daily sustained release verapamil (Verelan) modified these responses. We studied 13 patients with mild to moderate hypertension in a randomized, double-blind, placebo-controlled crossover trial. After 4 weeks of therapy, patients were evaluated following assumption of the upright posture, mental stress, and cold pressor test. During placebo, the stressors produced an increase in systolic pressure (144 +/- 2 to 167 +/- 3 mmHg, p < 0.001), heart rate (70 +/- 2 to 77 +/- 2 beats/ min, p < 0.001), and platelet aggregability to adenosine diphosphate (threshold concentration fell from 2.8 +/- 0.4 to 1.9 +/- 0.1 microM, p = 0.05) and epinephrine (3.4 +/- 0.9 to 1.6 +/- 0.6 microM, p < 0.001). Verapamil lowered systolic pressure at baseline (144 +/- 2 to 134 +/- 2 mmHg, p < 0.001), and after stress (167 +/- 3 to 154 +/- 3 mmHg, p < 0.001), but did not alter the absolute increase with stress. During verapamil, platelet reactivity did not increase with stress, and the post-stress response to epinephrine was reduced (higher threshold concentration) compared with placebo (3.9 +/- 1.3 vs. 1.5 +/- 0.3 microM, p = 0.05). Verapamil also reduced the response to collagen (increased lag time) at baseline and after stress (111 +/- 9 vs. 91 +/- 3 s, p < 0.01). We conclude that verapamil blunted potentially harmful stress-induced hemodynamic and hemostatic changes. Further studies are required to determine whether these effects translate into a lower incidence of acute cardiovascular events.

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).

Platelet aggregability in vivo is attenuated by verapamil but not by metoprolol in patients with stable angina pectoris

The effects of 1 month of treatment with either verapamil or metoprolol on several aspects of platelet function were studied at rest and during physical exercise or mental stress in patients with stable angina pectoris participating in the Angina Prognosis Study in Stockholm. Platelet aggregability was measured by filtragometry ex vivo, which reflects platelet aggregability in vivo and by Born aggregometry in vitro. Platelet secretion in vivo was assessed by measurements of beta-thromboglobulin in plasma. Verapamil reduced plasma norepinephrine levels (from 2.6 +/- 1.0 to 2.2 +/- 1.0 nmol/L; p < 0.01) and attenuated platelet aggregability at rest (filtragometry readings were prolonged from 219 to 295 seconds; p < 0.05, n = 46). Aggregability in platelet-rich plasma was not influenced. Metoprolol did not significantly affect filtragometry readings (n = 58) or aggregability in vitro (there was a tendency toward enhanced adenosine diphosphate sensitivity; p = 0.08). beta-thromboglobulin levels were low (approximately 25 ng/ml) and not influenced by either treatment. Physical exercise (bicycle ergometry) increased platelet aggregability in vivo both before and after drug treatment. Verapamil also attenuated platelet aggregability after exercise, whereas metoprolol had no such effect. Platelet function was not seriously altered by mental stress (Stroop's color word test) despite significant effects on hemodynamics and plasma catecholamines either before or after treatment with either drug. Thus, verapamil attenuates platelet aggregability in patients with stable angina pectoris, whereas metoprolol has no such effect.

Antihypertensive drug therapy does not perturb the circadian blood pressure pattern

The literature was reviewed to determine whether failure of older antihypertensive drugs to suppress the early morning increase of blood pressure was responsible, in part, for the less than satisfactory rate of reduction in cardiovascular mortality rates in the United States. The authors found that neither the old nor the new antihypertensive drugs altered the 24-hour blood pressure curve pattern, although long-acting drugs did show continued effect at the end of the 24-hour period when compared with placebo. The efficacy of these drugs most likely lies with their blood pressure lowering and other ancillary effects and not with pattern changes. More importantly, examination of new data (1989) shows that the rate of decline in death due to diseases of the heart has exceeded that for cerebrovascular diseases. Our overall health care effort may be more successful than we thought.