Secretory Dynamics of Growth Hormone in an Acromegalic Patient Associated with Graves' Disease*

Abstract

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.