Presence by Radioimmunoassay of a Calcitonin-Like Substance in Porcine Pituitary Glands*

Abstract
Acidic acetone extracts of whole porcine pituitary glands were studied for the presence of immunoreactive calcitonin (CT) using a porcine CT (pCT) RIA [radioimmunoassay] which did not react with other known pituitary hormones. Four preparations of porcine pituitary extract contained immunoreactive CT. Three of these displayed inhibition of binding parallel to that of authentic pCT in the pCT RIA and contained a single peak of immunoreactivity similar to pCT when studied by 2 different gel filtration chromatograpy systems. One preparation of procine pituitary extract showed nonparallelism in RIA dose-dilution experiments and multiple immunoreactive species both similar to and larger than pCT on gel filtration in 6 M guanidine HCl. The effect of the reduction of disulfide bonds, followed by carboxymethylation of sulfhydryl groups, on immunoreactivity and apparent molecular size was similar for the CT-like substance in porcine pituitary extract and for authentic pCT. Preliminary immunohistological studies showed cytoplasmic staining in cells of the porcine adenohypophysis. The porcine pituitary gland apparently contains a substance which has some of the immunochemical and biochemical properties of thyroidal pCT.