Intracellular distribution of amines and calcitonin in the sheep thyroid gland

Abstract

The distribution of amines (dopamine, histamine, 5-hydroxytryptamine, and norepinephrine) and calcitonin in the sheep thyroid gland was studied by quantitative analyses of these substances in subcellular fractions examined with the electron microscope. The fractions were prepared by centrifugation in continuous sucrose gradients. Histamine was mainly found in the supernatant fraction and dopamine in the gradient pellet together with mast cell granules. This indicates a release of histamine, but not of dopamine, from the mast cell granules, which contain both these amines. Norepinephrine was mainly recovered in the supernatant fraction and adjacent fraction. 5-Hydroxytryptamine and calcitonin were concentrated in one fraction. This fraction contained a high concentration of dense, argentaffin granules, indistinguishable from those found in sections of parafollicular cells. These observations show that 5-hydroxytryptamine and the polypeptide calcitonin are both stored almost exclusively in the cytoplasmic granules of the parafollicular cells.