Effects of high pressure on platelet aggregation in vitro

: An apparatus which enables aggregating agents to be added to a stirred suspension of platelets subjected to a pressure of up to 600 ATA is described. The ensuing aggregation reaction is monitored optically. The pressure is applied with helium; data are presented that indicate the effects are mainly attributable to hydrostatic pressure. The aggregation of human platelets induced by ADP was reversibly inhibited by pressure in the 1-270 ATA range. The second phase of aggregation was blocked by 65 ATA; the rate of first phase aggregation was reduced but the time to respond to ADP was not affected. Comparable pressures also affected collagen and arachidonate-induced aggregation. The time to respond to these aggregating agents was prolonged and both the rate and the degree of aggregation were reduced by pressure.