The hypothalamic-pituitary-thyroid axis.

Although recent investigations have contributed greatly to our understanding of the function and regulation of the hypothalamic-pituitary-thyroid axis, much remains unclear. The influence of suprahypothalamic areas of the brain on hypothalamic function, the nature of thyroid hormone feedback on the hypothalamus, and the physiologis sugnificance of prolactin release by TRH are all topics requiring further study. The extensive experience which has been accululated in the use of TRH as a diagnostic tool has led to its acceptance as a safe, convenient, rapid method of assessment of pituitary and thyroid function. It appears that TRH testing is useful in evaluation of pituitary TSH and prolactin reserve in patients with pituitary lesions; in the differentiation of pituitary and hypothalamic causes of hypothyroidism; in diagnosis of euthyroid Graves' disease; in the evaluation of the adequacy of TSH suppression in thyroid hormone therapy of nodular goiter; and possibly in the diagnosis of mild primary hypothyroidism.