Evaluation of the in vivo and in vitro calcium-regulating actions of noncalcitonin peptides produced via calcitonin gene expression.

Recent studies of rat and human calcitonin (CT) gene expression have uncovered a diversity of secretory peptides. Here we report the results of testing two such non-CT secretory peptides for CT-like action in live rats and in cultured fetal rat long bone. One peptide, the carboxyl-terminal CT-adjacent peptide that is cosynthesized with CT, has no hypocalcemic effect and no inhibitory action on bone resorption in vitro. The other peptide, CT gene-related peptide, lowers blood calcium and inhibits bone resorption. In vitro experiments are consistent with the idea that CT gene-related peptide is acting at CT receptors in bone.