Recent immunohistochemical demonstration of calcitonin in rat pituitary has suggested that calcitonin, in addition to ACTH, endorphins, lipotropins, and melanocyte-stimulating hormones might be derived from a 31,000-dalton glycoprotein percursor molecule. This immunoperoxidase study demonstrates a similar distribution for beta-endorphin and ACTH immunoreactivity in human pituitary; however, the two peptides are not necessarily present in the same cells at all times. Calcitonin could not be demonstrated in human pituitary under conditions suitable for demonstration of the peptide in thyroid C cells. Weakly positive immunostaining could be obtained only with much increase in antiserum concentration and length of incubation, and higher concentrations of calcitonin were needed to abolish staining in preabsorption studies. It thus appears that the immunoreactive calcitonin in human pituitary differs from that in thyroid C cells. Likewise, we could not demonstrate immunoreactive endorphin in any developmental stage of medullary thyroid carcinoma. Our study suggests that caution should be applied in considering a physiologic role for calcitonin in the pituitary and in postulating a common peptide origin for endorphin and calcitonin in humans.
G Mendelsohn, R D'Agostino, J C Eggleston, S B Baylin