Normalization of thyroid stimulating hormone levels in acromegalic patients after selective adenomectomy.

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Abstract
Changes in TSH secretion in 6 acromegalic patients were studied before and after transphenoidal adenomectomy (Hardy''s method) and compared to normal subjects and 6 patients with prolactinoma. Basal serum GH [growth hormone] levels ranging from 5 to over 250 ng/ml before adenomectomy decreased to below 5 ng/ml after the operation, and the abnormal responses of GH to TRH observed initially in 3 of the 6 patients almost disappeared in the postadenomectomy period. The response of serum TSH to TRH in acromegalic patients improved in each of the 6 patients after the operation. The TRH-stimulated TSH secretion in patients with prolactinoma of a site and grade similar to those in acromegalic patients was not so extremely low as that in the acromegalic subjects. As indicators of thyroid function, serum triiodothyronine (T3), thyroxine (T4), T3-uptake levels and free T4 indices did not change significantly after adenomectomy as compared with those before the operation in 5 of the 6 patients tested. Serum T3, T4 and T3-uptake levels and free T4 indices before adenomectomy were normal or subnormal in each patient except for a high serum T4 level and free T4 index before the operation in only 1 patient. It is difficult to conclude that the function of thyrotrophs was decreased by pressure upon the intact pituitary gland by the tumor, or that the thyroid gland also became hypertrophic secondary to the elevated GH, resulting in a large quantity of thyroid hormone being secreted, which caused a suppression of TSH secretion by negative feedback. Apparently, the secretion of GH and TSH from the intact pituitary glands is inhibited due to the autonomous production of excessive GH from the tumor, which may also suppress growth hormone releasing factor secretion and accelerate SRIF [somatostatin] secretion from the hypothalamus.