Explanation for Unusual Potency of Salmon Calcitonin

THE calcitonins are polypeptide hormones of thirty-two amino-acids which lower serum calcium in mammals by inhibiting bone resorption1. During evaluation of these hormones as a means of treating skeletal disorders in man, particularly Paget's disease of bone2, 3, the surprising observation was made that calcitonin from the salmon (SCT) is 20-200 times more potent than porcine calcitonin (PCT) and at least ten times more potent than human calcitonin3, 4. SCT is far more potent than any mammalian calcitonin yet tested in a wide variety of animal species5, 6. This unusual potency of salmon calcitonin could reflect either a greater hormone affinity for receptor sites or a greater resistance to metabolic destruction. We now report evidence which supports the latter possibility, infused SCT disappears from the circulation of the dog much more slowly than does PCT.