Species Specificity in the TSH Response to the Administration of l-Dopa

Summary

Acute administration of l-dopa (500-750 mg) lowered plasma TSH concentration and depressed an increase of plasma TSH in response to TRH in patients with primary hypothyroidism. In contrast, chronic administration of small or large doses of l-dopa failed to depress the development of goiter in rats treated with methimazole, indicating that plasma TSH concentration was not lowered by l-dopa in methimazole fed animals. Acute administration of l-dopa also failed to prevent an increase of intrathyroidal colloid droplets produced by an increase of TSH secretion in response to TRH. It is suggested that there is species specificity in the TSH response to the administration of l-dopa.