Hormone replacement therapy reduces the reactivity of monocytes and platelets in whole blood - A beneficial effect on atherogenesis and thrombus formation?

OBJECTIVE: Our purpose was to investigate the effects of hormone replacement therapy on the reactivity of monocytes and platelets in whole blood, measured by tissue factor activity, tumor necrosis factor-alpha, and thromboxane B-2. STUDY DESIGN: Thirty-two women were randomized into either transdermal or oral combined hormone replacement therapy and underwent blood sampling before and after 3 and 12 months of treatment. The tissue factor activity in monocytes was measured both in unstimulated whole blood and after a weak lipopolysaccharide stimulation. Tumor necrosis factor-alpha and thromboxane B-2 formation in plasma were measured after a weak lipopolysaccharide stimulation of whole blood. RESULTS: After 12 months of hormone replacement therapy there were significant reductions of tissue factor activity in both unstimulated and lipopolysaccharide-stimulated monocytes (p < 0.001) and significant reductions in the formation of tumor necrosis factor-alpha (p < 0.03) and thromboxane B-2 (p < 0.02). There were no differences in these parameters between the transdermal and the oral groups. No changes were observed after 3 months of therapy. CONCLUSION: Twelve months of hormone replacement therapy reduces cellular activation of blood monocytes and platelets; these changes may account for some of the beneficial effects in reducing the risk of cardiovascular disease.