Effects of exercise on cAMP-mediated platelet inhibition in young women: a pilot study.

Purpose: Exercise has been shown to reduce platelet reactivity and increase platelet sensitivity to prostacyclin, an endothelium-derived inhibitor of platelet activation, in middle-aged men and women. It is currently unknown if these beneficial effects can also be observed in young women and the intracellular mechanisms involved have not been identified. In this study, the feasibility of detecting changes in platelet reactivity, prostacyclin sensitivity and cAMP signalling were tested.

Methods: 10 well-trained and 10 sedentary but healthy young women participated in this study. Responses of washed platelets to thrombin receptor activating peptide 6, the thromboxane A₂ receptor agonist U46619, and prostaglandin E₁ were measured by light transmission aggregometry. Expression levels of proteins in the cAMP pathway including phosphorylation of the vasodilator-stimulated phosphoprotein were analysed by western blotting.

Results: There was no evidence of reduced basal reactivity in platelets from the well-trained group ( ${\dot{\text{V}}\text{O}}_{2\text{max}}$  = 51.1 ± 3.6 ml/kg/min) compared to the untrained group ( ${\dot{\text{V}}\text{O}}_{2\text{max}}$  = 31.1 ± 4.7 ml/kg/min). Platelets from the trained group showed evidence of greater sensitivity to the anti-aggregatory effects of prostaglandin E₁. The slope of the aggregation curves indicated an overall faster rate of aggregation in the untrained group. Mean phosphorylation levels of vasodilator-stimulating phosphoprotein were consistently higher in the trained group, indicative of increased protein kinase A activity.

Conclusion: Platelets from young women may exhibit an exercise-induced increase in sensitivity to prostacyclin leading to stimulation of the cAMP pathway. A larger study is warranted to explore this vasoprotective effect further.