Secretory dynamics of growth hormone in an acromegalic patient associated with Graves' disease

The dynamics of GH secretion were investigated in an acromegalic patient with Graves' disease during treatment with antithyroid drugs and radioactive iodine. The mean (+/- SE) basal plasma GH levels were 16.5 +/- 0.9 and 7.8 +/- 0.7 micrograms/L during the hyperthyroid and euthyroid states, respectively. There was a positive correlation (r = 0.902) between basal GH and free T4 levels. Twenty-four-hour plasma GH and urinary GH excretion both increased during the thyrotoxic state. Intravenous administration of TRH induced a marked increase in plasma GH levels during euthyroidism and a modest increase when the patient was hyperthyroid, whereas GH release induced by GH-releasing hormone was not altered by thyroid status. These findings suggest that hyperthyroidism stimulated spontaneous GH secretion from the pituitary adenoma, but inhibited the stimulating effect of TRH.