[Characterization of lipoprotein catabolism in biliary cholesterol hypersecretion conditions in rats]

The liver represents the principal pathway for sterol excretion from the organism. In addition, the major proportion of serum lipoproteins is catabolized in the liver. It is known that diosgenin and bean diet markedly induce biliary cholesterol output. In this series of studies we characterized the catabolism of several lipoprotein particles in animals fed diosgenin or a bean-rich diet (biliary cholesterol output is increased greater than 300% in these animals). Human low density lipoprotein (hLDL) and rat high density lipoprotein apo-E free (rHDL) were labeled with 125I. Rat chylomicrons were labeled with cholesterol-(3H)-oleate. hLDL clearance increased from 381 +/- 39 to 628 +/- 44 (microliters/h x 100 g body wt) (p less than 0.005) in bean-fed rats. The half life (t1/2) decreased from 12.4 +/- 1 to 9.8 +/- 0.7 h (p less than 0.005) in these rats. The clearance of rHDL apo-E free increased from 579 +/- 8 to 680 +/- 36 (microliters/h x 100 g body wt) (p less than 0.05) in diosgenin-fed animals. The t1/2 significantly decreased from 8.2 +/- 0.7 h to 7.0 +/- 0.3 h (p less than 0.05) in these rats. In contrast, chylomicron clearance and t1/2 were not modified by the diosgenin or bean diets. These results are consistent with the hypothesis that the number and/or affinity of the B/E and A-I receptors, but not E receptors are increased in rats fed biliary cholesterol hypersecretory diets. These studies suggests the presence of a functional inter-relationship between the biliary and sinusoidal pathways of hepatic cholesterol.