Effects of in vivo stimulation on molecular forms of circulatory calcitonin and calcitonin gene-related peptide in man.

Multiple molecular weight forms of the potent vasodilator peptide calcitonin gene-related peptide (CGRP) are present in the circulation in man. The monomeric form of CGRP(1-37) and CT(1-32) account for only a fraction of the total immunoreactive CGRP and calcitonin (CT) in the circulation. In vivo release of various molecular weight forms of CGRP and CT, including the monomeric form, into the circulation was demonstrated by gel-permeation chromatography, following stimulation of the gastrointestinal tract by a meal, and C-cells of the thyroid gland with pentagastrin. Following these stimulations an increase of the levels of C-terminal fragment of CGRP was also observed indicating a rapid metabolic breakdown of CGRP in vivo. In addition to a number of endogenous peptides and other substances, acute release of monomeric CGRP into the circulation may also contribute to the vasodilation observed following ingestion of food and administration of pentagastrin in man.