The effect of variable fat diets and cholesterol-lowering drugs on Antithrombin III levels in hyperlipoproteinemic and normal subjects.

Functional and immunological Antithrombin III (AT III) levels were studied in normal and hyperlipoproteinemic subjects undergoing crossover therapeutic trials of either diets or hypocholesterolemic drugs. The diet trial subjects, 7 hyperlipoproteinemics and 15 normals, were randomly assigned to crossover between a high saturated fat diet (P/S ratio 1:8) and a high polyunsaturated fat diet (P/S ratio 4:1) for periods of 6-8 weeks, preceded by a baseline period on regular American diet (P/S ratio 1:1). For the drug trials, 33 type II A or B hyperlipoproteinemics were treated in random and double-blind fashion with Colestipol (20 gm/day) or both, for periods of 3 months, preceded by a double placebo period. Mean low density lipoprotein cholesterol levels were significantly different (p less than 0.001) between high saturated and high polyunsaturated fat diets (157 +/- 37 mg/dl vs 137 +/- 31 mg/dl respectively, mean +/- S.D.) and between placebo and drug treatment periods (226 +/- 51 mg/dl vs 183 +/- 44 mg/dl respectively, mean + S.D.). There was no difference in basal functional or immunological AT III levels between normal and hyperlipoproteinemics. AT III levels did not correlate significantly with cholesterol or triglyceride levels and remained unchanged despite significant reductions in serum cholesterol related to the diet and drug therapy. There appears to be no significant association between baseline or post treatment serum cholesterol levels and functional or immunological AT III. Thus, changes in AT III are unlikely to play a role in the link between hypercholesterolemia and thrombosis.