Peptone‐mediated glucagon‐like peptide‐1 secretion depends on intestinal absorption and activation of basolaterally located Calcium‐Sensing Receptors

Abstract

Protein intake robustly stimulates the secretion of the incretin hormone, glucagon‐like peptide‐1 ( GLP‐1) but the molecular mechanisms involved are not well understood. In particular, it is unknown whether proteins stimulate secretion by activation of luminal or basolateral sensors. We characterized the mechanisms using a physiologically relevant model – the isolated perfused proximal rat small intestine. Intraluminal protein hydrolysates derived from meat (peptone; 50 mg/ mL) increased GLP‐1 secretion 2.3‐fold (from a basal secretion of 110 ± 28 fmol/min). The sensory mechanisms underlying the response depended on di/tripeptide uptake through Peptide Transporter 1 (PepT1) and subsequent basolateral activation of the amino acid sensing receptor, Calcium‐Sensing Receptor (Ca SR), since inhibition of PepT1 as well as Ca SR both attenuated the peptone‐induced GLP‐1 response. Supporting this, intraluminal peptones were absorbed efficiently by the perfused intestine (resulting in increased amino acid concentrations in the venous effluent) and infusion of amino acids robustly stimulated GLP‐1 secretion. Inhibitors of voltage‐gated L‐type Ca ²⁺ channels had no effect on secretion suggesting that peptone‐mediated GLP‐1 secretion is not mediated by L‐cell depolarization with subsequent opening of these channels. Specific targeting of Ca SR could serve as a target to stimulate the endogenous secretion of GLP‐1.