Effects of experimental hypothyroidism on the distribution of lipids and lipoproteins in the plasma of rats.

Male Sprague-Dawley rats were treated for up to 4 weeks with propylthiouracil in a study designed to determine the effects of experimental hypothyroidism on plasma lipoproteins. The distribution of lipid constituents across the plasma lipoprotein spectrum was assessed by size exclusion chromatography and the lipoprotein particle size was assessed by gradient gel electrophoresis. A reduction in the concentration of thyroid hormones was accompanied by changes to plasma lipoproteins within 1 week of commencing treatment with propylthiouracil. These changes progressed for a further week, after which the pattern remained relatively stable for up to 4 weeks of treatment. In the animals treated with propylthiouracil, there was a marked reduction in the concentration of all constituents of very-low-density lipoproteins (VLDL). There was a coincident increase in concentration of all constituents of low-density lipoproteins (LDL), with an increase in LDL triacylglycerol being particularly obvious. There was also a marked and sustained increase in the concentration of cholesterol in high-density lipoproteins (HDL), but in this case, there were no sustained increases in the concentrations of other HDL constituents. There was, however, an appearance of new populations of very large HDL particles comparable to the HDLc which accumulate in the plasma of cholesterol-fed animals.