Fig. 2
From: Secretion of glucagon, GLP-1 and GIP may be affected by circadian rhythm in healthy males
Diurnal rhythm of plasma concentrations of A) glucagon, B total GLP-1 and C) total GIP in 24 healthy males measured over 24 h. After an overnight fast the participants had 15 h of wakefulness (08 h-23 h) followed by a 9-h sleep opportunity (23 h-08 h) at the hospital ward. The sleep period is indicated with the grey area. The black arrows indicate time points for breakfast (9:30 h), lunch (13:00 h) and dinner (19:00 h). The red curves show the best fitting cosinor curve with confidence bounds for respectively A) plasma glucagon, B plasma total GLP-1 and C plasma total GIP. All three parameters fluctuate with a significant diurnal 24-h rhythm (all p < 0.0001). Plasma GIP fluctuates with the highest amplitude through day and night compared to plasma glucagon and plasma GLP-1. A boxplot and the full data set for respectively plasma glucagon, plasma GLP-1 and plasma GIP are also shown. The central box covers the 25th, 50th and 75th percentile. The whiskers marks 1.5*interquartile range (IQR). N = 22 for the first timepoint (t = 9 h), N = 24 for the rest of the remaining 8 time points. Conc.: concentration, GLP-1: Glucagon-like peptide-1, GIP: glucose-dependent insulinotropic polypeptide