CIRCULATING AND TISSUE FORMS OF THE INTESTINAL GROWTH-FACTOR, GLUCAGON-LIKE PEPTIDE-2

Glucagon-like peptide-2 (GLP-2) has recently been identified as a stim ulator of intestinal epithelial growth, prompting the development of R IA and HPLC methodologies to study this peptide in more detail. A GLP- 2-specific antiserum (UTTH-7) was developed that recognizes amino acid s 25-30 of human and rat GLP-2-(1-33). UTTH-7 crossreacts with N- and C-terminally modified forms of GLP-2, proglucagon, and the major progl ucagon fragment. Analysis of rat ileal extracts demonstrated the prese nce of GLP-2-(1-33) as well as significant amounts of GLP-2-(3-33) (16 +/- 7% of total GLP-2). The level of total immunoreactive GLP-2 in pl asma from fasted rats was 700 +/- 71 pg/ml, and this increased 3.6-fol d (P < 0.001) in 24-h fed rats. HPLC analysis demonstrated the presenc e of both GLP-2-(1-33) and GLP-2-(3-33) in plasma from fasted rats, wi th increments in both peptides in plasma from fed rats. Immunoreactive GLP-2 increased in plasma from human subjects 2 h after a meal, risin g from 851 +/- 230 to 1106 +/- 211 pg/ml(P < 0.05); 15 +/- 4% of this immunoreactivity was accounted for by the presence of intact GLP-2. HP LC showed the presence of both GLP-2-(1-33) and GLP-2-(3-33) in plasma from fed humans. Incubation of human GLP-2-(1-33) with the enzyme dip eptidylpeptidase TV resulted in liberation of GLP-2-(3-33), whereas re placement of Ala(2) with Gly(2) prevented this cleavage. Thus, while G LP-2-(1-33) is a major circulating and tissue form of GLP-2, GLP-2-(3- 33) is a significant component of immunoreactive GLP-2 in both intesti ne and plasma.