END‐ORGAN RESPONSES TO THYROXINE THERAPY IN SUBCLINICAL HYPOTHYROIDISM

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Abstract
Variables known to change with thyroid hormone status were studied in 18 patients with subclinical hypothyroidism, before and during treatment with thyroxine in a dose sufficient to restore the plasma TSH response to TRH to normal. There was an associated increase in both plasma total T4 [thyroxine] and free T4 within the normal range, but plasma total T3 [triiodothyronine] and free T3 were unchanged. As a result of thyroxine treatment, there was a small but significant increase (P < 0.05) in left ventricular ejection fraction (LVEF) with maximal exercise, but no significant changes in LVEF at rest and moderate exercise, continuously monitored mean sleeping heart rate, day/night ratios of urinary Na excretion, peripheral nerve conduction velocities, fasting serum triglycerides, total cholesterol (TC), high density lipoproteins (HDL) or TC/HDL ratios. Thyroxine replacement therapy apparently is not indicated in patients with subclinical hypothyroidism.