Definition: Given an abstract of a paper, generate a title for this paper such that conveys the key focus of the paper.
Input: Abstract: We observed quinidine-induced prolongation of bleeding time without thrombocytopenia in three subjects. In addition, we noticed a cumulative prolongation of bleeding time by a combination of quinidine and aspirin. We postulated that because both quinidine and aspirin inhibit epinephrine-induced platelet aggregation, a cumulative effect of the two drugs might be responsible for the hemostatic defect. In studies using normal human platelets, we confirmed a marked reduction in epinephrine-induced platelet aggregation by the combination of these two agents. To further study the potential mechanism of this cumulative effect, platelet lysates were incubated with the alpha 2-adrenoceptor antagonist tritiated yohimbine in the presence of quinidine and aspirin. On the basis of the radioligand binding data, the dissociation constant (KD) of alpha 2-adrenoceptors was observed to increase in the presence of quinidine as well as aspirin. The combination of these two agents caused a marked increase in the KD of platelet alpha 2-adrenoceptors without alteration in the number of receptor sites. These data suggest that the cumulative effects of quinidine and aspirin on platelet alpha 2-adrenoceptor KD may relate to the significant reduction in epinephrine-induced platelet aggregation. This phenomenon, coupled with other well-known effects of aspirin on the platelet release reaction and arachidonate metabolism, may lead to bleeding problems in some patients receiving this combination.

Cumulative effects of quinidine and aspirin on bleeding time and platelet alpha 2-adrenoceptors: potential mechanism of bleeding diathesis in patients receiving this combination.