Investigations on spontaneous aggregation and platelet responses to streptokinase and to adrenaline during pregnancy

Platelets have been shown to be hyperresponsive during pregnancy. Studies in whole blood have revealed increased 'spontaneous' platelet aggregation (SPA) and increased aggregation and (14)C-5HT release in response to adrenaline. Here we have extended previous studies. We have explored the possibility that the nature of the agent used to anticoagulate the blood may have influenced the results obtained, and, for the first time, have investigated the effects of streptokinase (SK) on platelets in whole blood during pregnancy. We found that increased SPA is present during pregnancy irrespective of the anticoagulant used. Also, platelets in blood taken during pregnancy aggregate more extensively in response to adrenaline, even though the type of anticoagulant influences the extent of (14)C-5HT release that accompanies the aggregation response. SK was found to induce platelet aggregation in whole blood and this was also independent of the anticoagulant used. Further, SK induced aggregation at a lower concentration than in blood from non-pregnant female volunteers (NFV). Increased platelet responses had always returned to values similar to those for NFV by 12 weeks post-natal. These studies confirm the existance of a generalized increase in platelet reactivity during pregnancy, indicate that this is not an artefact consequent to the use of a particular anticoagulant, and provide new information on the effects of SK on platelets during pregnancy.