Yet another study in favour of T3 - v- T4-only therapy

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J Clin Endocrinol

Metab. 2011 Aug 24. [Epub ahead of print]

Metabolic Effects of

Liothyronine Therapy in Hypothyroidism: A Randomized, Double-Blind, Crossover

Trial of Liothyronine Versus Levothyroxine.

Celi

FS, Zemskova

M, Linderman

JD,

S, Drinkard

B, Sachdev

V, Skarulis

MC, Kozlosky

M, Csako

G, Costello

R, Pucino

F.

Source : Diabetes, Endocrinology, and Obesity

Branch (F.S.C., M.Z., J.D.L., S.S., M.C.S., F.P.), National Institute of

Diabetes and Digestive and Kidney Diseases; Rehabilitation Medicine Department

(B.D.), Clinical Center; Translational Medicine Branch (V.S.), National Heart,

Lung, and Blood Institute; and Departments of Nutrition (M.K.) and Laboratory

Medicine (G.C., R.C.), National Institutes of Health, Bethesda, land 20892.

Abstract

Context:

Levothyroxine (l-T(4)) therapy is based on the assumption that the conversion

of T(4) into T(3) provides adequate amounts of active hormone at target

tissues. However, in rodents, l-T(4) alone does not restore a euthyroid state

in all tissues. Previous combination l-T(4)/liothyronine (l-T(3)) therapy

trials focused on quality-of-life endpoints, and limited information is

available on the effects on other measures of thyroid hormone action.

Objective: Our objective was to evaluate the efficacy of thyroid hormone

replacement with l-T(4) or l-T(3) at doses producing equivalent normalization

of TSH. Participants, Design, and Setting: Fourteen hypothyroid patients

participated in this randomized, double-blind, crossover intervention at the

National Institutes of Health Clinical Center. Interventions: l-T(3) or l-T(4)

were administered thrice daily to achieve a target TSH from 0.5-1.5 mU/liter.

Volunteers were studied as inpatients after 6 wk on a stable dose and at the

target TSH. Main Outcome Measures: Serum thyroid hormones, lipid parameters,

and indices of glucose metabolism were evaluated. Results: No difference was

observed in TSH between l-T(3) and l-T(4) treatments. l-T(3) resulted in

significant weight loss [l-T(4), 70.6 ± 12.5, vs. l-T(3), 68.5 ± 11.9 kg (P =

0.009)] and in a 10.9 ± 10.0% decrease in total cholesterol (P = 0.002), 13.3 ±

12.1% decrease in low-density lipoprotein-cholesterol (P = 0.002), and an 18.3

± 28.6% decrease in apolipoprotein B (P = 0.018). No significant differences

were observed in high-density lipoprotein-cholesterol, heart rate, blood

pressure, exercise tolerance, or insulin sensitivity. Conclusions: The substitution of l-T(3) for l-T(4) at

equivalent doses (relative to the pituitary) reduced body weight and resulted

in greater thyroid hormone action on the lipid metabolism, without detected

differences in cardiovascular function or insulin sensitivity.