IN-VIVO AND IN-VITRO STUDIES OF THE ROLE OF HDL IN PLATELET ACTIVATION IN NORMOTENSIVE AND HYPERTENSIVE SUBJECTS

The influence of high density lipoproteins (HDL) on platelet function were examined in vivo and in vitro. Intraplatelet, ionised calcium con centrations ([Ca2+](i)) were measured using the fluorescent dye Quin-2 . In vitro, platelet responses to AVP were measured in the presence or absence of HDL. Pre-treating platelets from normal volunteers with HD L in vitro lowered the [Ca2+](i) response to AVP but did not significa ntly affect basal values. In vivo, plasma lipoprotein profiles in norm otensive (13 men, 17 women) and hypertensive (13 men, 11 women) subjec ts were compared with basal and AVP-stimulated platelet [Ca2+](i) valu es. Plasma [HDL] were not related to basal or stimulated [Ca2+](i). Pl asma cholesterol concentrations were higher in the hypertensive patien ts largely because low density lipoprotein [LDL] were raised in male h ypertensive patients. Plasma [LDL] and total plasma cholesterol correl ated negatively with basal [Ca2+](i) (but not with AVP-stimulated valu es) only in this subgroup. In hypertensive patients, AVP-stimulated [C a2+](i) (but not basal values) were lower than normotensive controls. From in vitro studies, it may be concluded that the anti-atherogenic p roperties of HDL might be mediated by inhibition of platelet reactivit y. However, ex vivo a negative influence of LDL on basal (not stimulat ed) [Ca2+](i) appears to be paramount.