Effect of thyroid hormone on plasma apolipoproteins and ApoA‐ and ApoB‐containing lipoprotein particles

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Abstract
Methods: Apolipoprotein and apoB‐ and apoA‐containing lipoprotein particle concentrations were determined in 10 athyreotic patients 4 weeks after withdrawal of Synthroid replacement therapy [T4, 0.96 ± 0.66 μg mL−1; thyroid‐stimulating hormone (TSH), 62.7 ± 22.8 μIU mL−1] and again 4 weeks after reinstitution of treatment.Results: Thyroid hormone replacement was associated with significant decreases in plasma cholesterol (TC), triglyceride (TG), apolipoprotein B and apolipoprotein C‐III (P < 0.01). Both the cholesterol ester‐rich LP‐B particles and triglyceride‐rich LP‐Bc particles declined significantly in response to thyroid hormone (LP‐B withdrawal 81.6 ± 24.0 vs. replacement 65.1 ± 22.0; LP‐Bc withdrawal 14.3 ± 6.0 vs. replacement 10.9 ± 4.8 mg%, P < 0.01). ApoC‐III also decreased in high‐density lipoprotein (HDL) (apoC‐III‐HS) and in very low‐density lipoprotein (VLDL) + low‐density lipoprotein (LDL) (apoC‐III‐HP), but this reduction was proportionate so that the apo‐C‐III‐HS/apoC‐III‐HP ratio, an indirect estimate of the efficiency of lipoprotein lipase (LPL), was unchanged. Apolipoprotein A‐I concentrations also decreased significantly (withdrawal 140.7 ± 27.0 vs. replacement 127.1 ± 30.0 mg%, P < 0.01) in parallel with the changes in LP‐A‐I and LP‐A‐I:A‐II particles (LP‐A‐I withdrawal 35.8 ± 7.7 vs. replacement 31.5 ± 6.3; LP‐A‐I:AII withdrawal 104.9 ± 20.0 vs. replacement 95.5 ± 26.0; P < 0.05).Conclusion: These findings indicate that thyroid hormone influences the transport not only of both TG‐rich and cholesterol‐rich apoB‐containing lipoprotein particles but also of those that contain apoAI.

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