Total GLP-1 concentrations in plasma were measured by radioimmunoassay after extraction of plasma with 70 % ethanol (vol/vol, final concentration) using antiserum 89390 which has an absolute requirement for the intact amidated carboxy-terminus of GLP-1 7–36 amide and crossreacts fully with GLP-1 9–36 amide, the primary metabolite of dipeptidyl-peptidase −4 mediated degradation.
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