Summary
A study has been made of the biochemical factors underlying the platelet response
to laser-induced microvascular injury. A platelet aggregating substance is produced
at sites of laser-induced injury which markedly stimulates platelet activity at a
site of injury inflicted a short distance downstream. Distal sites of injury are not
similarly influenced if the distance between the injuries is increased or if the proximal
site no longer shows platelet-stimulating activity. The stimulating effect of an adjacent
proximal injury on platelet activity at a distal site is inhibited by local intra-arterial
infusion of adenosine. Measurements of arterial blood pressure and microvascular blood
flow velocity during adenosine infusion showed that its inhibitory effect on platelet
activity is largely independent of its vasodilator properties. The effect of infusion
of different adenosine phosphates (AMP, ADP, ATP) was also studied. Very small amounts
of ADP markedly stimulated platelet activity and the emboli formed were similar to
those normally produced at sites of laser injury. At high concentration AMP inhibited
while ATP stimulated platelet activity in vivo. The results emphasise the fundamental
role of ADP as a mediator of the platelet response at sites of laser- induced microvascular
injury.
