Thyroid function in patients with hyperprolactinaemia: relationship to dopaminergic inhibition of TSH release

It has been reported recently that patients with hyperprolactinaemia may develop hypothyroidism as a consequence of the increased inhibition of TSH release by dopamine which occurs in the majority of such patients. In this study we have evaluated thyroid function in a large number of hyperprolactinaemic patients in order to delineate more precisely the relationship between thyroid status, free thyroid hormone levels and the control of TSH release by dopamine. Biochemical euthyroidism was present in the majority of the hyperprolactinaemic patients. Our data indicate that the increased dopaminergic inhibition of TSH release does not lead to hypothyroidism. Instead, the slightly elevated basal TSH levels and TSH responses to TRH (within the normal range) may reflect the operation of a compensatory mechanism to maintain euthyroidism in the face of te increased inhibition of TSH release by hypothalamic dopamine.