Fig. 4.

Measurement of circulating metabolic hormones ((A) leptin; (B) total and acylated ghrelin; (C) insulin; (D) total glucose-dependent insulinotropic peptide (GIP); (E) total glucagon-like peptide 1 (GLP-1)) in rats under different pre-analytical conditions. The first graph for each hormone shows absolute concentrations under different pre-analytical conditions separately for each rat. For better comparison of the different pre-analytical conditions, a second bar chart for each hormone depicts the effects in relation to the concentration obtained from serum (n=9/condition). Therefore, the serum concentration has been set to 100% and other conditions are expressed as a percentage thereof (*p<0.05, **p<0.01, ***p<0.001). Abbreviations: “RT”: room temperature; “Prot.”: addition of a general protease inhibitor; “Prot.+DPP-4”: addition of a general and a specific DPP-4 inhibitor; “Prot.+HCl”: addition of a general protease inhibitor and acidification of the sample with HCl. Data in bar charts are expressed as means±SEM.