Improved Insulin Sensitivity during Pioglitazone Treatment Is Associated with Changes in IGF-I and Cortisol Secretion in Type 2 Diabetes and Impaired Glucose Tolerance

Background. Hypercortisolism and type 2 diabetes (T2D) share clinical characteristics. We examined pioglitazone's effects on the GH-IGF-I and HPA axes in men with varying glucose intolerance. Methods. 10 men with T2D and 10 with IGT received pioglitazone 30–45 mg for 12 weeks. OGTT with microdialysis in subcutaneous adipose tissue and 1 μg ACTH-stimulation test were performed before and after. Glucose, insulin, IGF-I, IGFBP1, and interstitial measurements were analyzed during the OGTT. Insulin sensitivity was estimated using HOMA-IR. Results. HOMA-IR improved in both groups. IGF-I was initially lower in T2D subjects (P=0.004) and increased during treatment (−1.4±0.5 to −0.5±0.4 SD; P=0.007); no change was seen in IGT (0.4±39 SD before and during treatment). Fasting glycerol decreased in T2D (P=0.038), indicating reduced lipolysis. Fasting cortisol decreased in T2D (400±30 to 312±25 nmol/L; P=0.041) but increased in IGT (402±21 to 461±35 nmol/L; P=0.044). Peak cortisol was lower in T2D during treatment (599±32 to 511±43, versus 643±0.3 to 713±37 nmol/L in IGT; P=0.007). Conclusions. Pioglitazone improved adipose tissue and liver insulin sensitivity in both groups. This may explain increased IGF-I in T2D. Pioglitazone affected cortisol levels in both groups but differently, suggesting different mechanisms for improving insulin sensitivity between T2D and IGT.