Circulating obestatin levels in normal and Type 2 diabetic subjects

Background: Obestatin has been discovered as a new product of the ghrelin gene. Its physiological actions are still a matter of debate, but it seems that this peptide is likely to be involved in the control of insulin secretion and action as well as of adipocyte function. It has been already shown that obestatin secretion in humans is negatively modulated by food intake. Aim: To clarify obestatin secretion in normal subjects and in patients with Type 2 diabetes (T2D) in basal conditions and after a standardized meal. Subjects/methods: Five normal subjects and 5 T2D patients were studied during infusion of saline (iv for over 5 h from -120 to +180 min). A standardized lunch was served at 0 min. Obestatin, glucose, and insulin levels were assayed at -120, -90, -60, -45, -30, -15, 0, 15, 30, 45, 60, 90, 120, 150, and 180 min. Results: From -120 to 0 min, obestatin levels in normal and T2D subjects were similar (area under the curve: 32.3±5.6 pg/ml/min vs 31.1±1.0 pg/ml/min). After the meal, circulating obestatin levels underwent a clear decrease in normal subjects (0 min: 300.6±34.7 pg/ml vs nadir at 60 min: 161.8±29.4 pg/ml; p=0.002) but not in diabetic patients (0 min: 267.2±16.5 pg/ml vs nadir at 180 min: 226.0±10.5 pg/ml). Conclusion: This study shows that normal and diabetic subjects display similar levels of circulating obestatin in fasting condition. However patients with T2D look refractory to the inhibitory effect of meal on obestatin secretion.