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Thyroxine Replacement Therapy Enhances Clearance of Chylomicron Remnants in Patients with Hypothyroidism

Department of Internal Medicine C, Metabolic Unit and Institute of Endocrinology, Tel Aviv-Elias Sourasky Medical Center, and The Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 64239, Israel

Address all correspondence and requests for reprints to: Itamar Grosskopf, M.D., Department of Internal Medicine C, Tel Aviv-Elias Sourasky Medical Center, 6 Weizman Street, Tel Aviv 64239, Israel. E-mail: igrossko{at}tasmc.health.gov.il

To further confirm the benefit of replacement therapy in terms of risk for coronary artery disease, we evaluated the effect of T₄ on postprandial lipoproteins in patients with hypothyroidism. Nine normolipidemic patients (aged 62.75 ± 7.6 yr) with TSH of 32.2 ± 13.2 mU/L and free T₄ of 0.66 ± 0.17 ng/mL were treated with T₄ (50–100 µg/day) for at least 4 months. The behavior of postprandial lipoproteins was assessed before and during treatment by determining retinyl palmitate levels in the total plasma, chylomicrons (S_f >1000) and chylomicron remnants (S_f < 1000) fractions for 8 h after a mixed meal plus vitamin A. During T₄ treatment, serum levels of TSH and FT₄ were 4.4 ± 4.9 mU/L and 1.2 ± 0.34 ng/mL (P = 0.001 and P = 0.002), respectively. Fasting low density lipoprotein cholesterol decreased from 166 ± 35 to 135 ± 23 mg/dL (P = 0.035). Retinyl palmitate (RP) levels in the chylomicron remnant fraction was reduced significantly during therapy from 6948 ± 2790 to 5174 ± 2401 µg/L·h (area under the curve ± SD; P = 0.014). Total plasma RP and chylomicron RP remained unchanged. We conclude that T₄ enhances the clearance of chylomicron remnants in normolipidemic patients with hypothyroidism.

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