Effects of dietary cholesterol and hypothyroidism on rat apolipoprotein mRNA metabolism.

The effects of dietary cholesterol and hypothyroidism on the mRNA levels of rat apolipoproteins A-I, A-IV, and E were measured in extracts of rat liver and rat intestine by hybridization to specific cDNA. Four groups, each comprised of six rats, were fed diets consisting of normal laboratory rat chow and either no supplements (control); 5% lard, 1% cholesterol, and 0.3% taurocholic acid (CF); 5% lard, 1% cholesterol, 0.3% taurocholic acid, and 0.1% propylthiouracil (CF-PTU); or 0.1% propylthiouracil (PTU) for 32 days. At the conclusion of the diets, serum cholesterol, triiodothyronine, and thyroxine levels were measured. The average serum cholesterol concentrations for the four groups were 50.4 +/- 3.7, 75.6 +/- 15.3, 135.3 +/- 41.5, and 73.3 +/- 16.4 mg/dl, respectively. The presence of propylthiouracil in the diets significantly lowered triiodothyronine and thyroxine levels in the serum. The mRNA levels for apolipoproteins A-I and A-IV in rat liver decreased significantly after the feeding of the CF-PTU diet (31 +/- 4% and 32 +/- 3% of normal, respectively) and the PTU diet (34 +/- 8% and 43 +/- 12% of normal, respectively), but showed little change after the CF diet (88 +/- 16% and 108 +/- 15% of normal, respectively). The effects of dietary propylthiouracil on the hepatic mRNA levels for apolipoproteins A-I and A-IV imply a role for thyroid hormones in regulating the mRNA levels for these apolipoproteins in rat liver. ApoE mRNA levels in the rat liver decreased slightly after the CF-PTU diet (74 +/- 12% of normal) and after the PTU diet (73 +/- 10% of normal).(ABSTRACT TRUNCATED AT 250 WORDS)