Calcium stimulates the release of calcitonin gene-related peptide from the canine thyroid

The calcitonin gene in the thyroid parafollicular cells generates two different mRNAs, which encode for the precursors of calcitonin and calcitonin gene-related peptide (CGRP). In this study, we investigated whether these two peptides are released simultaneously in the perfused dog thyroid. The isolated dog thyroid (n = 10) was once-through perfused with a Krebs-Ringer bicarbonate buffer. After elevation of the buffer Ca2+ concentration from 1.5 to 2.5 mM, a rapid, marked, and parallel secretion of both calcitonin and CGRP occurred (P less than 0.001). By stepwise increase of the buffer Ca2+ concentration, it was found that, although an elevation from 1.5 to 1.65 mM had no influence on the thyroid output of calcitonin or CGRP, elevations to 1.75, 2.0, and 2.5 mM of Ca2+ induced dose-dependent parallel increases in the thyroid output of calcitonin and CGRP. Furthermore, the stimulation with pentagastrin (100 pM) increased the thyroid output of both calcitonin and CGRP in parallel. It is concluded that the normal dog thyroid releases calcitonin and CGRP in parallel on stimulation with Ca2+ and pentagastrin.