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Lipoproteins, Lipolytic Enzymes, and Hormonal Status in Hypothyroid Women at Different Levels of Substitution^*

TIMO KUUSI, MARJA-RIITTA TASKINEN and ESKO A. NIKKILÄ

Second and Third Departments of Medicine, University of Helsinki Helsinki, Finland

Address all correspondence and requests for reprints to: Timo Kuusi, M.D., Second Department of Medicine, University of Helsinki, Haartmaninkatu 4, 00290 Helsinki, Finland.

Serum lipoproteins and postheparin plasma lipoprotein lipase and hepatic lipase (HL) activities were determined in 23 hypothyroid women treated with graded doses of thyroxine (T₄) (50,100, and 150 µg/day), each given for 3 weeks. Since the sex hormone-binding globulin (SHBG) and thereby serum sex steroid concentrations are sensitive to thyroid status, we also measured serum testosterone, estradiol, and SHBG at each time. Stepwise T₄ treatment resulted in gradual improvement in thyroid status. Concomitantly, serum low density lipoprotein (LDL) cholesterol decreased in a linear fashion from a mean of 4.72 ± 0.31 (±SEM) to 3.21 ± 0.18 mmol/L (P < 0.001) after the largest dose. In contrast, serum high density lipoprotein (HDL) cholesterol decreased, although not in a dose-dependent fashion, from 1.61 ± 0.07 to 1.44 ± 0.05 mmol/L (P < 0.001) after the largest dose. Serum SHBG increased along with improvement of thyroid function, but this increase did not have major impact on the changes in LDL during T₄ treatment, as judged by multiple regression analysis. Thus, serum LDL correlated independently only with T₄ (r = –0.38; P < 0.001). The serum HDL changes were almost exclusively due to those in the HDL₂ subfraction, and these were related to HL activity, which increased from 13.4 ± 1.76 to 18.9 ± 2.08 U/L after the largest dose. We conclude that thyroid hormones regulated serum HDL (HDL₂) cholesterol mainly through their effect on HL.

^* This work was supported by grants from the Finnish State Medical Research Council, the Meilahti Foundation, and the University of Helsinki.

Deceased, September 21,1986.

Received May 1, 1987.

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