Patterns of prolactin secretion in the syndrome of general resistance to thyroid hormones

The dynamics of TSH and PRL secretion were studied in three patients with incomplete generalized resistance to thyroid hormones. Results in the first patient differed from those in the other two. The first patient had been treated previously with radioiodine but was clinically euthyroid when subsequently treated with supraphysiological quantities of T3 and T4. Increasing doses of T4 from 0.2-0.3 mg/day caused a decline in serum TSH levels and lesser increments in TSH to injected TRH in this patient. The other two patients had not been treated, but had basal TSH levels and TSH responses to TRH similar to those in the first patient. However, the TSH response to injected metoclopramide in the first patient was substantially higher than the responses in the other two patients. The basal levels of PRL in the first patient were elevated at both T4 doses; also, her PRL responses to TRH and metoclopramide were exaggerated and, compared to normal values, disproportionate to her TSH responses to these provocative agents. In contrast, the other two patients had normal basal PRL concentrations and normal or near-normal PRL responses to TRH and metoclopramide. We conclude that within the syndrome of resistance to thyroid hormones, there are heterogeneous patterns of PRL secretion. Dopaminergic tone on thyrotrophs and lactotrophs also differs among patients with the syndrome.