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

Abstract

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.

Effects of L-thyroxine Replacement Therapy on Carotid Intima-media Thickness in Patients with Primary Hypothyroidism

“…It has been demonstrated that thyroid hormone increases the breakdown of LDL cholesterol by increasing both the number and activity of LDL receptor ( Chait et al, 1979 ;Thompson et al, 1981 ). Other additional potential atherogenic eff ects of hypothyroidism over lipid metabolism are reversible decrease in the cleaning of chylomicron residuals ( Weintraub et al, 1999 ), decrease of the cholesterol ester transfer protein activity including the reverse cholesterol transport way ( Tan et al, 1998 ) and decrease of the activity of lipoprotein lipase and hepatic lipase ( Lam et al, 1986 ). Interestingly, Nagasaki et al (2003) found a signifi cant decrease in the total cholesterol, triglyceride levels, the ratio of total cholesterol / HDL cholesterol, and LDL cholesterol levels in the control measurements after an euthyroid status was achieved in patients with hypothyroidism ( Nagasaki et al, 2003 ).…”