Endocrine Abstracts

Overt hypothyroidism (OH) and more controversially subclinical hypothyroidism (SCH) are associated with abnormal lipid metabolism and endothelial dysfunction under fasting conditions. Little data exists regarding the metabolic and vascular effects of OH or SCH under postprandial conditions.

We aimed to characterize postprandial metabolism with emphasis on intestinally derived lipoproteins, HDL-cholesterol (HDL-C) and endothelial function in patients with OH, SCH and normal subjects.

Subjects were studied fasting and for 8-h following a mixed-meal. Apolipoprotein (Apo) B48, a marker of intestinally-derived lipoproteins was measured by ELISA. Systemic and HDL-associated inflammation was assessed by measuring serum-amyloid-A (SAA)-levels. HDL was subfractionated into HDL2 and 3 by rapid ultracentrifugation. Cholesteryl-ester-transfer-protein (CETP), which mediates transfer of cholesterol from HDL to triglyceride-rich lipoproteins and LDL-cholesterol (LDL-C) was measured in HDL2 and 3 subfractions. Flow-mediated-dilatation (FMD) of the brachial artery was measured to assess endothelial dysfunction.

Compared to normal subjects, postprandial ApoB48 AUC was greater in OH and SCH while postprandial HDL-C was lower in SCH but not OH. There were no significant between-group differences in LDL-C, triglycerides, or SAA. HDL2- and 3-associated CETP activity was lower in OH compared to normal and SCH subjects. FMD was reduced in OH compared to SCH and normal subjects postprandially.

Postprandial lipoprotein and vascular abnormalities differ between OH and SCH. Although both are characterized by increased intestinally-derived lipoprotein particles, HDL-C is reduced only in SCH. Maintained HDL-C in OH probably reflects reduced CETP, which was not observed in SCH. Postprandial endothelial dysfunction is abnormal only in OH and does not appear to reflect increased inflammation.