Thyroxine replacement therapy enhances clearance of chylomicron remnants in patients with hypothyroidism

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 microg/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 (Sf >1000) and chylomicron remnants (Sf <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 microg/L x 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.