SYNTHESIS AND BIOLOGICAL-ACTIVITY OF C-TERMINALLY TRUNCATED FRAGMENTSOF HUMAN ALPHA-CALCITONIN GENE-RELATED PEPTIDE

C-terminally truncated fragments of human alpha-calcitonin gene-relate d peptide (h-alpha-CGRP) were tested for their ability to stimulate am ylase secretion from pancreatic acinar cells and relax precontracted m esenteric arteries. h-alpha-CGRP, h-alpha-CGRP (1-36), h-alpha-CGRP (1 -35), and h-alpha-CGRP (1-34) were made by Merrifield's solid-phase pe ptide synthesis methodology. Peptides were purified by gel filtration, cation-exchange chromatography, and semipreparative reversed-phase hi gh-performance liquid chromatography. The products were characterized by amino acid analysis, mass spectrometry, and tryptic digestion. h-al pha-CGRP stimulated amylase secretion from dispersed guinea pig pancre atic acini in a biphasic concentration-dependent manner. The initial i ncrease in amylase secretion reached 8% of total cellular amylase cont ent with an ED50 value of 7.7 nM, and the second increase reached 11% of total cellular amylase content at a concentration of h-alpha-CGRP o f 10(-4)M. h-alpha-CGRP (1-36) caused a small, significant increase in amylase release. C-terminally truncated fragments h-alpha-CGRP (1-35) and h-alpha-CGRP (1-34) did not increase amylase release at concentra tions <10(-5) M. At concentrations > 10(5) M the fragments h-alpha-CGR P (1-35) and h-alpha-CGRP (1-34) caused a smaller increase in amylase release than that caused by h-alpha-CGRP whereas h-alpha-CGRP (1-36) c aused the same increase. h-alpha-CGRP caused a concentration-dependent relaxation of rat mesenteric artery, precontracted with prostaglandin F2alpha, with an EC50 of 2.9 nM and a maximal relaxation that was 60% of the prostaglandin F2alpha-induced tone. h-alpha-CGRP (1-35) also r elaxed the mesenteric artery in a concentration-dependent manner with a maximum response that was 40% of the prostaglandin F2alpha-induced t one. The remaining fragments did not relax rat mesenteric arteries. Ad ditionally, h-alpha-CGRP (1-36) and h-alpha-CGRP (1-34) did not block h-alpha-CGRP-induced relaxation of the mesenteric artery. An intact C- terminus is required for h-alpha-CGRP to cause potent biological effec ts in pancreatic acini and mesenteric artery. The different effects of h-alpha-CGRP (1-35) in mesenteric artery compared with those in pancr eatic acini suggest that the CGRP receptors in these two tissues may b e different.