Age-related changes in platelet microviscosity and aggregation in rats

1. To study possible changes in platelet microviscosity in aged animals, 1, 6-diphenyl-1,3,5-hexatriene (DPH) was used as a nonpolar probe embedded in thrice-washed platelets from young, adult and aged rats. With the known val ues of maximum limiting anisotropy and the structural parameter of DPH and by estimating the steady state of fluorescence anisotropy and the average f luorescence of lifetime, we applied the Perrin equation to calculate the mi croviscosity, 2. We measured platelet aggregation, platelet lipids and platelet polyunsat urated fatty acids to determine any causal relationship between these param eters. Platelet aggregation, the platelet molar ratio of cholesterol to pho spholipid ([C]/[PL]) and platelet microviscosity increased with age (P < 0. 05) and were correlated with one another (P < 0.05), 3, Age-dependent increases in the steady state of fluorescence anisotropy, order parameters and the short component of fluorescence lifetime of the fl uorophore were expressed as functions of variables, such as microviscosity or the [C]/[PL] ratio, 4, Platelet concentrations of arachidonic and eicosapentaenoic acids increa sed with age, but were not associated with aggregation. Age-related changes in microviscosity and the [C]/[PL] ratio seemed to be determinants affecti ng biophysical properties of platelet aggregation.