β-cell Function During a High Fat Meal in Young versus Old Adults: Role of Exercise.

The acute effect of exercise on β-cell function during a high fat meal (HFM) in young (YA) vs. old (OA) adults is unclear. In this randomized cross-over trial, YA (n=5M/7F, 23.3±3.9y) and OA (n=8M/4F, 67.7±6.0y) underwent a 180 min HFM (12 kcal/kgbw; 57% fat, 37% CHO) after a rest or exercise (~65% HRpeak) condition ~12hr prior. After an overnight fast, plasma lipids, glucose, insulin, as well as FFA were determined for peripheral, or skeletal muscle, insulin sensitivity (Matsuda Index) as well as hepatic (HOMA-IR) and adipose (Adipose-IR) insulin resistance calculations. β-cell function was derived from C-peptide and defined as early (0-30min) and total phase (0-180min) disposition index (DI, glucose-stimulated insulin secretion (GSIS) adjusted for insulin sensitivity/resistance). Hepatic insulin extraction (HIE) body composition (DXA) and VOpeak were also assessed. OA had higher TC, LDL, HIE and DI across organs as well as lower adipose-IR (all, <0.05) and VOpeak (=0.056) despite similar body composition and glucose tolerance. Exercise lowered early phase TC and LDL in OA vs. YA (<0.05). However, C-peptide AUC, total phase GSIS, and adipose-IR were reduced post-exercise in YA vs. OA (<0.05). Skeletal muscle DI increased in YA and OA after exercise (<0.05), while adipose DI tended to decline in OA (=0.06 and =0.08). Exercise-induced skeletal muscle insulin sensitivity (r=-0.44, =0.02) and total phase DI (r=-0.65, =0.005) correlated with reduced glucose AUC. Together, exercise improved skeletal muscle insulin sensitivity/DI in relation to glucose tolerance in YA and OA, but only raised adipose-IR and reduced adipose DI in OA.