Ultrastructural localization of calcitonin and somatostatin in C cells of rabbit thyroid

C cells of rabbit thyroid exhibit significant differences in morphology, namely a variable nuclear structure and differences in size and osmophility of secretory granules. An examination of serial sections of these cells was made, using the immunocytochemical PAP or protein A-gold procedures. All C cells, irrespective of their morphology, were found to store both calcitonin and somatostatin in all secretory granules. The physiological role of somatostatin in calcitonin secretion by C cells is discussed.