RELATIONSHIPS BETWEEN PLASMA THYROTROPIN RECEPTOR ANTIBODIES AND LIPID OR LIPOPROTEIN PARAMETERS IN GRAVES-DISEASE

Functional thyrotropin receptors (TSH-R) have recently been detected i n fat cells but not in liver cells from rat, and it seems that in infa nt adipocytes stimulatory TSH-R antibodies (TSH-R-ab) act through this receptor pathway, resulting in increased triglyceride catabolism. We investigated the relationships between plasma TSH-R-ab and free thyrox ine (FT4) levels and plasma lipid or lipoprotein values in 49 untreate d adult women with Graves' disease, all positive for these antibodies. A simple positive correlation (p < 0.01) was found between TSH-R-ab l evels and FT4 values (r = 0.40). Simple positive correlations (p < 0.0 01) were found between triglyceride levels and FT4 (r = 0.51) or TSH-R -ab (r = 0.52) values. Multiple regression analysis confirmed that bot h FT4 and TSH-R-ab are strong (p < 0.005) predictors of triglyceride ( FT4: partial r = 0.40; TSH: partial r = 0.39). Simple negative correla tions (p < 0.05, at least) were found between FT4 levels and total cho lesterol (TC) (r = -0.45), low-density lipoprotein (LDL)-C (r = -0.46) , apoprotein (apo)-B (r = -0.31) or high-density lipoprotein (HDL)-C ( r = -0.55) values. Among these lipid parameters, only HDL-C levels (r = -0.31, p < 0.05) correlated to TSH-R-ab values. However, multiple re gression analysis revealed that while FT4 is a strong predictor (p < 0 .005) of TC (partial r = -0.42), LDL-C (partial r = -0.43) or HDL-C (p artial r = 0.47), TSH-R-ab are not. Thus, the apparent positive relati onship between TSH-R-ab and HDL-C results from the positive correlatio n between TSH-R-ab and FT4. In conclusion, this study suggests that st imulating TSH-R-ab are involved in triglyceride metabolism. In contras t to thyroid hormones, these antibodies seem not to be related to chol esterol metabolism.