The growth hormone, prolactin and TSH response to TRH and L-dopa in patients with hyperprolactinaemia and a normal-sized sella turcica may denote a pituitary adenoma.

Forty-one patients with hyperprolactinaemia and suspected prolactinomas were studied. Growth hormone (GH) and thyrotropin (TSH) secretory patterns after thyrotropin releasing hormone (TRH) were affected in the majority of patients. The disturbances were observed regardless of tumour size as indicated by the radiological sella size. In patients with hyperprolactinaemia and normal-sized sella turcica, an abnormal GH and TSH response to TRH can be helpful in the diagnosis of a microadenoma. The hyperprolactinaemia per se and its effect on dopaminergic hypothalamic neurones may be the cause of the GH and TSH response. By contrast, many patients with macroprolactinomas showed insufficient GH secretory capacity.