Reduced insulin clearance contributes to the increased insulin levels after administration of glucagon-like peptide 1 in mice

Aims/hypothesis: Glucagon-like peptide-1 (GLP-1) is known to be a potent stimulator of insulin secretion. How- ever, whether GLP-1 also affects insulin clearance is not known. To explore this, we developed a technique to determine prehepatic insulin secretion in mice, based on deconvolution of plasma C-peptide concentrations. The estimated beta cell se- cretion was then related to plasma insulin levels to allow de- termination of clearance rate of endogenously produced insulin. Materials and methods: Kinetic parameters of C-peptide were estimated after i.v. injection of human C-peptide (0.8 or 3 nmol/ kg) or glucose (1 g/kg), either alone or together with GLP-1 (10 nmol/kg), in anaesthetised NMRI mice. Results: C-peptide was distributed in two compartments (distribution volume 11.4±0.4 ml, 42±2% of which was in the accessible com- partment). Fractional C-peptide clearance was 8.2±0.6% of the total distribution volume per minute. GLP-1 mark- edly enhanced prehepatic insulin secretion; more than 80% of prehepatic secretion occurred during the first minute after injection. Fractional clearance of endogenously re- leased insulin after glucose was 0.66±0.11 min-1 and this was reduced to 0.36±0.10 min-1 by GLP-1 (p=0.04). Conclusions/interpretation: It is possible to perform C-pep- tide deconvolution for estimating prehepatic insulin secre- tion in mice. GLP-1 reduces the clearance of endogenously released insulin; therefore, it may affect insulin levels by increasing prehepatic insulin secretion and by reducing in- sulin clearance.