Improvement of insulin resistance following transsphenoidal surgery in patients with acromegaly: Correlation with serum IGF-I levels

Aim: The aim of this study was to determine the correlation between the growth hormone (GH)-insulin-like growth factor-I (IGF-I) axis and glucose intolerance in acromegaly during the early postoperative period. Subjects and Methods: The study included 20 patients with acromegaly caused by GH-secreting pituitary adenoma who received transsphenoidal surgery in our hospital. Glucose tolerance was evaluated with oral glucose tolerance tests (OGTTs) performed during pre-and early postoperative periods (9 [7-18] days after surgery). Homeostasis model assessment of insulin resistance (HOMA-IR) and insulinogenic index (IGI) were calculated, and correlation analyses were performed between these values and the GH-IGF-I axis. Patients were divided according to postoperative changes of the axis, and glucose tolerance was compared between the groups. Results: In preoperative OGTTs, nine patients had impaired glucose tolerance and two had diabetes mellitus patterns. Postoperatively, significant reduction was observed both in fasting plasma glucose levels (p < 0.01) and in HOMA-IR (p < 0.01), whereas IGI showed no significant change. HOMA-IR was significantly correlated with serum IGF-I levels both before (r=0.83, p < 0.01) and after (r=0.57, p < 0.01) surgery, although it was not correlated with serum GH levels. Patients who achieved more than 50% postoperative reduction in serum IGF-I levels showed significant improvement in OGTTs results (p < 0.05). Conclusions: In patients with acromegaly, serum IGF-I levels, but not GH levels, were significantly correlated with insulin resistance. Early postoperative improvement of glucose tolerance is observed in patients who achieved postoperative reduction in serum IGF-I levels.