Suppression of Elevated Serum TSH Levels in Hypothyroidism by Fusaric Acid

Abstract

The effect of Fusaric acid (FA), a specific inhibitor of dopamine β-hydroxylase, on human TSH and thyroid hormone concentration (T₄ and T₃) was evaluated. Healthy subjects showed no significant changes in serum T₃, T₄ and TSH concentrations following the administration of FA calcium salt (FA-Ca) or placebo. Similarly, administration of FA-Ca for 4 weeks to hypertensive patients failed to produce significant changes in the serum T₄ or T₃ Resin Sponge Uptake values, and in the TSH and T₃ responses to TRH. In contrast, FA-Ca produced a significant reduction on thehigh basal serum TSH level in patients with primary hypothyroidism. The mean nadir was 25% and ranged from 6 to 61%. As in the case of L-Dopa, the effect of FA-Ca on serum TSH is most clearly demonstrated in patients with primary hypothyroidism. Alterations in brain amines may directly or indirectly suppress pituitary TSH secretion. The possibility of changes in the peripheral distributionor turnover rateof TSH has not been excluded.