In the pig, the C cells of the thyroid gland, which are the counterparts of parafollicular cells of Nonidez in the thyroid of the dog, are mainly epifollicular rather than parafollicular.
Using guinea-pig anti-pig calcitonin, and an indirect ('sandwich') technique, immunofluorescence tests indicated that calcitonin in the pig thyroid is present in cells which are morphologically indistinguishable from the C cells. Calcitonin was also present in cells which resemble pericytes.
Taking advantage of cross-reactivity between canine calcitonin and anti-pig calcitonin antibody, a similar localization (C cells and pericytes) could be shown by immunofluorescence tests in the thyroid of dogs.
These results confirm previous work indicating that the parafollicular cells are responsible for the production and secretion of thyrocalcitonin. The role of the pericytes has not been established with certainty.