Lipoproteins from normolipidemic and dyslipidemic subjects modify the thromboxane A2 generation by platelets in clotting human blood.

The study was performed to investigate the influence of lipoproteins (LP) on the thromboxane (TX) A2 formation capacity of platelets in clotting whole blood in vitro. The different lipoprotein fractions VLDL, LDL, HDL2 and HDL3 were isolated from blood of normo- or dyslipidemic volunteers by ultracentrifugation. These lipoproteins were incubated in blood with different levels of serum total cholesterol (TC) taken from normolipidemics (TC < 200 mg/dl), moderate hypercholesterolemics (TC: 200-250 mg/dl) or subjects with high cholesterol level (TC > 250 mg/dl), respectively. The amount of serum TXA2 formed within 60 min at 37 degrees C was measured by enzyme immunoassay. The results obtained show that the efficacy of separate LP fractions to influence the TXA2 production depends not only on the type of LP fraction but also on the source of plasma used for isolation of LP and on the cholesterol level in the blood for incubation: LDL taken from normolipidemics or moderate hyperlipidemics inhibited the TXA2 formation in blood from normolipidemics (P < 0.02, respectively), but enhanced it in blood from persons with moderate hypercholesterolemia (P < 0.05). LDL from hyperlipidemics enhanced TXA2 production in blood from hyperlipidemics (P < 0.05). The HDL2 fractions inhibited the TXA2 formation in blood from normo- and hypercholesterolemics (P < 0.02, resp.), but there was no effect of HDL2 in clotting blood from persons with moderate hypercholesterolemia. All HDL3 fractions tested inhibited the TXA2 formation in all types of blood used for clotting (P < 0.02, resp.), probably due to their great cholesterol accepting capacity.

[Effect of hydrocortisone on lipid composition of blood serum lipoproteins in the development of experimental atherosclerosis]. / Vliianie kortizola na lipidnyi sostav lipoproteidov syvorotki krovi pri zksperimental'nom steroskleroze

Single administration of hydrocortisone into rabbits with experimental atherosclerosis increased the content of atherogenous classes of lipoproteins (Low Density Lipoproteins (LDL) and Very Low Density Lipoproteins (VLDL) in the animals with distinct atheromatosis. Content of the lipoproteins was decreased in animals, which had no atheromatous alterations in aorta under the effect of atherogenous diet. Within 5 hrs after the single administration of hydrocortisone in rabbits with pronounced atheromatosis of aorta relative content of cholesterol was increased in the VLDL fraction. In rabbits, resistant to development of atheromatosis, composition of VLDL was not altered. Under the effect of hydrocortisone the LDL fraction fo lipid composition was altered in the direction of relative increase in triglycerides content. In the LDL fractions subfractions were observed, which were similar to the VLDL in their cholesterol/triglycerides ratios. The data obtained suggest that in blood plasma transformation of the lipoproteins was impaired under the effect of hydrocortisone. Hydrocortisone influenced the spectrum and lipid composition of lipoproteins in blood serum independently of the degree of hypercholesterolaemia.