Summary
The effect of the depressor active substance (DAS) on platelets of men, cats, pigs, dogs, rats, and rabbits has been studied by the method of Born (1962). DAS was found to induce platelet aggregation only in human and feline platelet rich plasma (PRP). Nevertheless, there are some striking similarities between platelet aggregation induced by DAS and ADP (i.e. inhibition by the same compounds, such as adenosine, tosylarginine methylester, or p-chloromercuribenzoic acid). The species specifity and a marked tachyphylactic action on platelets of both species makes DAS clearly discernible from all the other aggregation inducing substances which have been studied so far. From additional experiments there is evidence that DAS acts on human and cat platelets via a release reaction of cellular substances known to enhance platelet aggregation in a second phase. This process is strongly dependent on the presence of Ca++.
