POSTPRANDIAL HORMONE AND METABOLIC RESPONSES IN SIMULATED SHIFT WORK

This study was designed to investigate postprandial responses to a mix ed meal in simulated shift work conditions. Nine normal health subject s (six males and three females) were studied on two occasions at the s ame clock time (1330 h) after consuming test meals, first in their nor mal environment and secondly after a 9 h phase advance (body clock tim e 2230 h). Plasma glucose, insulin, glucose-dependent insulinotropic p olypeptide (GIP), glucagon-like peptide-1 (GLP-1), triacylglycerol (TA G) and non-esterified fatty acids (NEFAs) were determined at intervals for 6 h after each test meal. Postprandial. plasma glucose, insulin, GIP and GLP-1 profiles were evaluated by calculating areas under the c urve (AUG) for the first 2 h and the last 4 h of the sampling together with total AUC. Significantly higher postprandial glucose responses ( total AUC) were observed after the phase shift than before (AUC 0-360 min, 2.01 (1.51-2.19) vs 1.79 (1.56-2.04) mmol/l.min; P<0.02; mean (ra nge)). No significant difference was observed wh en the first 2 h of e ach response was compared, but significantly higher glucose levels wer e observed in the last 4 h of the study after the phase shift than bef ore (AUC 120-360 min, 1.32 (1.08-1.42) vs 1.16 (1.00-1.28) mmol/l.min; P<0.05). Similar results were obtained for insulin (AUG 0-360 min, 81 .72 (30.75-124.97) vs 58.98 (28.03-92.57) pmol/l.min; P<0.01; AUC 120- 360 min, 40.73 (16.20-65.25) vs 25.71 (14.25-37.33) pmol/l.min; P<0.02 ). No differences were observed in postprandial plasma GIP and GLP-1 r esponses before and after the phase shift. Postprandial circulating li pid levels were affected by phase shifting. Peak plasma TAG levels occ urred 5 h postprandially before the phase shift. Postprandial rises in plasma TAG were significantly delayed after the phase shift and TAG l evels continued to rise throughout the study. Plasma postprandial NEFA levels fell during the first 3 h both before and after the phase shif t. Their rate of return to basal levels was significantly delayed afte r the phase shift compared with before. This study demonstrates that a simulated phase shift can significantly alter pancreatic B-cell respo nses and postprandial glucose and lipid metabolism.