Prenatal development of the cat thyroid: immunohistochemical demonstration of calcitonin in the "C" cells

Summary The presence of calcitonin in the cat thyroid was studied immunohistochemically in a series of gland development. the first positive cells are to be found on the 38th day of gestation, i.e. 1–2 days after level nine of ontogenetic development has been reached. The cytoplasm of these cells form only a narrow border round the nucleus. With advancing development the bumber of calcitonin-positive and its amount increases. From approximately the 50th day of prenatal development, the initially diffusely scattered, solitary calcitonin-positive cells are gradually replaced by groups of cells, which begin to occupy a characteristic position in relation to the follicular epithelium. The largest quantity of calcitonin-positive cells is found in foetuses about to be born.In non-pregnant adult cats, the incidence of immunohistochemically calcitonin-reactive cell is more sporadic and their distribution in the lobes of the thyroid is uneven.