COOH-terminally extended secretins are potent stimulants of pancreatic secretion

Posttranslational processing of preprosecretin generates several COOH-termi nally extended forms of secretin and alpha-carboxyl amidated secretin. We u sed synthetic canine secretin analogs with COOH-terminal -amide,-Gly, or -G ly-Lys-Arg to examine the effects of COOH-terminal extensions of secretin o n bioactivity and detection in RIA Synthetic products were purified by reve rse-phase and ion-exchange HPLC and characterized by reverse-phase isocrati c HPLC and amino acid, sequence, and mass spectral analyses. Secretin and s ecretin-Gly were noted to coelute during reverse-phase HPLC. In RIA using e ight, different antisera raised against amidated secretin, COOH-terminally extended secretins had little or no cross-reactivity. Bioactivity was asses sed by measuring pancreatic responses in anesthetized rats. Amidated canine and porcine secretins were equipotent. Secretin-Gly and secretin-Gly-Lys-A rg had potencies of 81 +/- 9% (P > 0.05) and 176 +/- 13% (P < 0.01), respec tively, compared with amidated secretin, and the response to secretin-Gly-L ys-Arg lasted significantly longer These data demonstrate that 1) amidated secretin and secretin;Gly are not separable under some chromatographic cond itions, 2) current RIA may not detect bioactive COOH-terminally extended fo rms of secretin in tissue extracts or blood, and 3) the secretin receptor m ediating stimulation of pancreatic secretion recognizes both amidated and C OOH-terminally extended secretins.