The psysiological role of calcitonin assessed through chronic calcitonin deficiency in rats.

1. An attempt was made to assess the physiological role of calcitonin by producing its prolonged deficiency in rats.2. Three groups of young rats viz. (I) sham-operated controls, (II) thyroidectomized with thyroxine replacement and (III) thyroidectomized with thyroxine as well as calcitonin replacement, all with parathyroid autografts, were studied for 5 weeks. Groups II and III showed impaired Ca tolerance and group II also showed significant reduction in total (organic and inorganic) mass of femora as compared to group I.3. Three similar groups of old mature rats were studied as under (2) for 9 weeks. Groups II and III in this case showed no significant changes as compared to group I.4. In intact mature rats, Ca tolerance is impaired, thyroid content of calcitonin is high and the hypocalcaemic action of calcitonin is much reduced as compared to intact young rats.5. It is concluded that calcitonin plays a useful but non-essential role in Ca metabolism and bone development of young growing rats. Its function, if any, in mature rats on a normal diet remains doubtful.