Localization of immunoreactive calcitonin gene‐related peptide in thyroid C cells from various mammalian species

Localization of immunoreactive calcitonin gene-related peptide (CGRP) in thyroid C cells from various mammalian species was investigated by the immunoperoxidase method. In many animal species including dogs, cats, cattle, monkeys, rats, and rabbits, almost all C cells revealed an intense immunoreactivity for CGRP; the cytoplasm of C cells was filled with reaction products for CGRP. In these animal species, calcitonin and CGRP coexisted in the C cells. However, in some species including pigs, mice, hamsters, and guinea pigs, the CGRP immunoreactivity of C cells was weak or negative. It was concluded that there was a considerable variation in CGRP immunoreactivity of C cells from species to species. In rabbits and guinea pigs, almost all C cells were also intensely immunoreactive to antisomatostatin antiserum, whereas in other animal species including dogs, cats, cattle, monkeys, rats, pigs, mice, and hamsters only a few C cells were immunoreactive to somatostatin. Three peptides--calcitonin, somatostatin, and CGRP--are synthesized alone in rabbit C cells. Thus, there was no relation between CGRP and somatostatin concerning the existence of both peptides in thyroid C cells.