The immunoreactive serum human growth hormone (hGH), prolactin (PRL), and thyroid-stimulating hormone (TSH) concentrations were measured after administration of 500 μg of thyrotropin-releasing hormone (TRH) intravenously (iv) in 8 patients with acromegaly before and after transnasal transsphenoidal microdissection hypophysectomy and 3 patients after transfrontal hypophysectomy. Other pituitary function tests were also assessed. The hGH, PRL, and TSH responses to TRH administration in these patients were compared to those found in 12 normal subjects of the same age range and sex. The hGH response to TRH in these patients was compared to that found after intravenous insulin tolerance (ITT), arginine infusion and oral glucose tolerance (GTT) tests. The serum hGH concentration rose significantly in all the acromegalic patients after TRH administration before therapy, while no rise was seen in normals. In the majority of patients studied, the rise of hGH level after ITT, iv arginine and oral GTT was not as high or as frequent. After therapy, some of the patients who had basal serum hGH levels within normal range (less than 10 ng/ml) continued t o have abnormal rise in hGH after TRH administration. Serum PRL levels rose in all acromegalic patients after TRH administration and fell significantly after treatment. Three acromegalics had abnormally high serum PRL levels at basal and during TRH administration. TSH response to TRH was within the low normal range in the majority of patients studied before therapy. Ten of the 11 patients studied after hypophysectomy showed diminished TSH reserve but only 7 showed signs of hypothyroidism by other criteria. These results indicate: 1) High serum hGH levels at basal and TRH stimulation may aid in establishing the diagnosis of acromegaly. 2) High hGH in acromegalic patients after TRH administration may persist after therapy in spite of a normal basal hGH level. 3) TRH stimulation in acromegalics before and after therapy may show the hGH, PRL, and TSH pituitary reserve.
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Samaan et al. (1974) studied this question.