Preoperative growth hormone response to thyrotropin-releasing hormone and oral glucose tolerance test in acromegaly: a retrospective evaluation of 50 patients.

ABSTRACT

The objective of this study was to investigate the relationship between growth hormone (GH) dynamic tests (thyrotropin-releasing hormone [TRH] test and oral glucose tolerance test [OGTT]), insulin-like growth factor-I (IGF-I) plasma values, tumor size, and clinical outcome in patients with GH-secreting pituitary adenomas. Furthermore, we investigated the potential prognostic utility of the above biochemical parameters in the follow-up of patients with acromegaly. We studied 50 acromegalic patients (18 males and 32 females; mean age, 40 years; range, 16 to 69) who underwent trans-sphenoidal removal of a GH-secreting pituitary adenoma from 1990 to 1994. Preoperatively, we evaluated (1) GH plasmatic levels after an oral glucose load (OGTT) (blood samples were drawn at -15, 0, 30, 60, 90, 120, 150, and 180 minutes after oral administration of 0.75 g/kg body weight [BW] of glucose), (2) GH plasma levels after a TRH test (200 microg as an intravenous [IV] bolus), and (3) basal IGF-I plasma levels after an overnight fast. From 3 to 12 months after surgery we evaluated (1) GH plasma values after an OGTT, and (2) basal plasma IGF-I, free triiodothyronine (FT(3)), free thyroxine (FT(4)), thyroid-stimulating hormone (TSH), and urinary free cortisol. The same tests were performed every year for 5 years. All of the patients were classified into 4 subgroups according to the system of Hardy and Vezina. Preoperatively, "controlled" patients (n = 29) had a GH paradoxical response to TRH (n = 28) and an unresponsiveness to OGTT (n = 29); 23 of them belonged to the I and II classes. Only 5 poorly controlled patients (n = 21) showed a preoperative paradoxical response to TRH and 9 had a preoperative GH partial inhibition after OGTT; 19 of them belonged to the III and IV classes. Our data suggest that in the preoperative period in acromegalic patients the simultaneous presence of a GH paradoxical response to TRH and lack of GH inhibition after OGTT is inversely related to the tumor size and therefore more likely to be restored to normal by surgical treatment.