Effects of pravastatin on cholesterol metabolism in Watanabe heritable hyperlipidemic rabbits.

Pravastatin, a competitive inhibitor of hydroxymethylglutaryl CoA reductase (HMG CoA reductase) is a potent hypocholesterolemic agent in humans as well as experimental animals, including the Watanabe heritable hyperlipidemic (WHHL) rabbit, lacking low density lipoprotein (LDL) receptor activity. We studied the effect of pravastatin on several aspects of cholesterol metabolism in WHHL rabbits. Cholesterol synthesis was measured by intraperitoneal injection of radioacetate and determination of its incorporation into the nonsaponifiable lipid fraction of liver, plasma, adrenal glands and gonads. A single dose of pravastatin (25 mg/kg) caused statistically significant inhibition of hepatic cholesterol synthesis at 2, 6, 12, and 24 hours following oral administration. By 48 hours, the inhibitory effect of the drug was no longer demonstrable. The pattern of radioactivity in the plasma was similar to that in the liver. The drug had no statistically significant effect on cholesterol synthesis in adrenal glands and gonads, suggesting a selective effect on the liver. Cholesterol absorption was studied after simultaneous oral administration of [3H] cholesterol and [14C] beta-sitosterol. Pravastatin, 50 mg/kg for 10 days had no effect on fecal excretion of the radiolabelled steroids over 4 days. At 24 hours the plasma level of [14C] cholesterol was 1/3 that of control in pravastatin treated animals (p < 0.05) but did not undergo an accelerated decline over 6 days. The activity of acyl CoA: cholesterol acyltransferase (ACAT) in intestinal mucosa and the concentration of hepatic cholesterol were similar in animals treated over one year with pravastatin 50 mg/kg/day or with placebo. Our data do not allow us to make definitive conclusions about the effect of pravastatin on cholesterol absorption but are compatible with the hypothesis that the drug inhibits the hepatic synthesis as well as the assembly of cholesterol into lipoproteins.

Pravastatin decreases serum lipids and vascular cholesterol deposition in Watanabe heritable hyperlipidemic (WHHL) rabbits.

The effects of long term administration of pravastatin (a competitive inhibitor of hydroxymethylglutaryl CoA reductase) were assessed by measuring serum lipids and aortic and coronary atherosclerosis in Watanabe Heritable Hyperlipidemic (WHHL) rabbits. Six-month-old WHHL rabbits were given either 50 mg/kg/day of the drug or vehicle. The rabbits were sacrificed following 6 or 12 months of treatment and serum cholesterol and triglycerides and aortic cholesterol and hydroxyproline were measured. Atherosclerotic plaques in the aorta and coronary arteries were quantified with morphometric methods. Mean serum cholesterol +/- SEM (n) in the control vs. pravastatin groups after 6 months were: 535 +/- 34 (11) vs. 411 +/- 22 (12) (p less than 0.005) and after 12 months 458 +/- 43 (9) vs. 309 +/- 29 mg/dl (12) (p less than 0.005). In the pravastatin group, percent aortic area covered with plaque and aortic cholesterol content were reduced 35% (ns) and 55% (p less than 0.05) at 6 months, and 26% (ns) and 44% (ns) at 12 months, respectively. Little difference was found in serum triglycerides and aortic hydroxyproline in the 2 groups. There was strong correlation of serum cholesterol with aortic cholesterol content (r = 0.61, p less than 0.003) and with the percent aortic plaque area (r = 0.67, p less than 0.001), at 12 months. Morphometric analysis of wall thickness and lumen area of major coronary arteries revealed no significant differences in the 2 groups. In conclusion, pravastatin effectively lowered the serum cholesterol level in an animal model defective in low density lipoprotein receptors; this reduction was strongly correlated with amelioration of such atherosclerotic processes as lipid deposition and plaque formation.