Summary
In serum incubated at 36° C for 18-24 hours a factor (DAS) develops which on intravenous
injection into cats evokes platelet aggregation followed by an increase in pulmonary
vascular resistance (PVR). This change in PVR is mediated via the platelets since
it significantly correlates with the preinjection platelet count. There is evidence
that phosphatidic acids (PA) and lysophosphatidic acids (LPA) are the active components
of DAS. Investigations performed on platelet-rich plasma from man, cat, pig, dog,
rabbit, guinea pig, and rat demonstrate that only human and feline platelets exposed
to PA or to LPA are aggregated. Feline platelets are more sensitive to either compound
than are the platelets from men; however, human platelets exhibit two exceptional
properties, a) the sensitivity rapidly declines with time, b) pretreatment with subthreshold
concentrations of LPA or PA induces a specific tachyphylaxis.
