1902-P: Insulin Pulses Do Not Inhibit Glucagon Secretion in Nondiabetic Humans

Abstract

Type 2 diabetes (T2DM) is characterized by defects in insulin secretion and glucagon suppression. It has been assumed that defective glucagon secretion arises due to impaired insulin secretion. Indeed, prior work suggests that pulsatile insulin secretion has an inverse relationship with post-prandial glucagon secretion. However, more recent data suggest that dysregulation of glucagon secretion in prediabetes occurs early, and independently, of changes in insulin secretion. During a series of experiments examining the mechanisms underlying prediabetes, we studied 29 nondiabetic subjects (age = 44 ± 2, BMI 28 ± 1 Kg/m2). Hepatic vein catheterization allowed sampling of insulin and glucagon at 2 minute intervals during fasting and during a hyperglycemic clamp (150mg/dL). Mean insulin concentrations rose from fasting (33 ± 1 vs. 144 ± 2 pmol/L, p<0.01) while glucagon was suppressed (96 ± 1 vs. 62 ± 1 ng/L, p<0.01) during the clamp. A cross-correlation analysis of the two hormones showed, on average, a small in-phase coordination between insulin and glucagon pulses during fasting, which inverted during hyperglycemia (0.2 ± 0.1 vs. -0.4 ± 0.1, p<0.01). Subsequently, Cross-Approximate Entropy (Cross-ApEn), a technique for comparing synchronicity between two time series, was used to evaluate their interaction. This showed a moderate level of synchronicity, unaffected by glucose concentrations, whether calculated using glucagon as the template to assess pattern reproducibility in insulin concentration (0.78 ± 0.03 vs. 0.76 ± 0.03, fasting vs. hyperglycemia), or when using insulin as the template for the glucagon pattern (0.78 ± 0.02 vs. 0.76 ± 0.03, fasting vs. hyperglycemia). The values of Cross-ApEn did not differ between the two scenarios, suggesting the interaction between the two hormones is not driven by either. Overall these data suggest that, on a minute-to-minute basis, direct control and secretion of glucagon is not mediated (or restrained) by insulin. Disclosure M.C. Laurenti: None. C. Dalla Man: Research Support; Self; Sanofi-Aventis Deutschland GmbH. R.T. Varghese: None. R.A. Rizza: None. A. Matveyenko: None. C. Cobelli: None. A. Vella: Advisory Panel; Self; vTv Therapeutics, Zealand Pharma A/S. Research Support; Self; Novo Nordisk A/S, Xeris Pharmaceuticals, Inc. Funding National Institutes of Health (DK78646, DK116231)