Synthesis and Biological Activity of C-Terminally Truncated Fragments of Human α-Calcitonin Gene-Related Peptide

C-terminally truncated fragments of human α-calcitonin gene-related peptide (h-α-CGRP) were tested for their ability to stimulate amylase secretion from pancreatic acinar cells and relax precontracted mesenteric arteries. h-α-CGRP, h-α-CGRP (1–36), h-α-CGRP (1–35), and h-α-CGRP (1–34) were made by Merrifield's solid-phase peptide synthesis methodology. Peptides were purified by gel filtration, cation-exchange chromatography, and semipreparative reversed-phase high-performance liquid chromatography. The products were characterized by amino acid analysis, mass spectrometry, and tryptic digestion. h-α-CGRP stimulated amylase secretion from dispersed guinea pig pancreatic acini in a biphasic concentration-dependent manner. The initial increase in amylase secretion reached 8% of total cellular amylase content with an ED₅₀ value of 7.7 nM, and the second increase reached 11% of total cellular amylase content at a concentration of h-α-CGRP of 10⁻⁴M. h-α-CGRP (1–36) caused a small, significant increase in amylase release. C-terminally truncated fragments h-α-CGRP (1–35) and h-α-CGRP (1–34) did not increase amylase release at concentrations <10⁻⁵ M. At concentrations >10⁻⁵ M the fragments h-α-CGRP (1–35) and h-α-CGRP (1–34) caused a smaller increase in amylase release than that caused by h-α-CGRP whereas h-α-CGRP (1–36) caused the same increase. h-α-CGRP caused a concentration-dependent relaxation of rat mesenteric artery, precontracted with prostaglandin F_2α, with an EC₅₀ of 2.9 nM and a maximal relaxation that was 60% of the prostaglandin F_2α-induced tone. h-α-CGRP (1–35) also relaxed the mesenteric artery in a concentration-dependent manner with a maximum response that was 40% of the prostaglandin F_2α-induced tone. The remaining fragments did not relax rat mesenteric arteries. Additionally, h-α-CGRP (1–36) and h-α-CGRP (1–34) did not block h-α-CGRP-induced relaxation of the mesenteric artery. An intact C-terminus is required for h-α-CGRP to cause potent biological effects in pancreatic acini and mesenteric artery. The different effects of h-α-CGRP (1–35) in mesenteric artery compared with those in pancreatic acini suggest that the CGRP receptors in these two tissues may be different.