A dual effect of calcitonin gene-related peptide on plasma calcium levels in the chick

Calcitonin gene-related peptide (CGRP) lowers plasma calcium in the rat and inhibits bone resorption by isolated rat osteoclasts. In our preliminary studies we found that rat CGRP elevates plasma calcium levels in the chick, a response that was somewhat similar to that of parathyroid hormone. Here, we report that human CGRP (α) produces a concentration-dependent elevation of plasma calcium levels. The two peptides did not follow precisely the same time course. Whereas at 15 minutes CGRP produced hypocalcaemia relative to the control plasma calcium levels, at 30 minutes both CGRP and PTH were found to be hypercalcaemic. These studies suggest that CGRP initially interacts with the calcitonin receptor to produce a calcitonin-like effect, which is followed by hypercalcaemia presumably by antagonising the action of endogenous circulating calcitonin.