Endocrine Abstracts

Background: Active acromegaly is characterized by decreased insulin sensitivity (ISen). However, insulin secretion (ISec) may not increase satisfactorily to compensate for the low ISen.

Aim: To assess ISen and ISec and to calculate disposition index (DI) using an intravenous glucose tolerance test (IVGTT) in patients with active acromegaly.

Methods: Twelve patients (7 men, 5 women) with active acromegaly and 2 normal subjects (2 men) underwent a standard IVGTT with a glucose dose of 0.3 g/kg of body weight. Eight patients had normal glucose tolerance (NGT) and 4 had impaired glucose tolerance (IGT). None were on medication for acromegaly of glucose intolerance. ISen was calculated as the slope of the glucose curve between 10 and 75 min (the rate of glucose disappearance) divided by the area under the insulin curve between 0 and 75 min. ISec was calculated as the acute insulin response, the delta area under the insulin curve between 2 and 10 min after glucose infusion. DI was calculated as ISen times ISec.

Results: Subjects with NGT (8 patients with acromegaly and 2 normal subjects) had a significantly higher DI than patients with IGT (801 (632, 1762) vs. 172 (98, 247); P<0.001). Inside the IGT group there were both patients with extremely low ISen (0.02 L×100 000/pmol×min) and unsatisfactorily increase in ISec (3862 pmol×min/l) and patients with nearly normal ISen (1.09 L×100 000/pmol×min) but very low ISec (244 pmol×min/l).

Conclusion: Both insulin sensitivity and insulin secretion contribute to glucose intolerance in acromegaly. DI clearly differentiate glucose intolerant patients from glucose tolerant ones.