Response of calcitonin cells, parathyroid glands and bone to prolonged calcitonin administration in the Indian palm squirrel, Funambulus pennanti (Wroughton).

The administration of calcitonin (4 MRC units injected intraperitoneally daily for 42 days) caused hypocalcaemia, hypophosphataemia and a decrease in the serum acid phosphatase level in adult Indian palm squirrels, Funambulus pennanti. Hypocalcaemia and the decrease in the serum acid phosphatase level persisted up to 21 days but the hypophosphataemic effect continued throughout the experiment. The serum calcium level increased from day 28 up to day 35 and the serum acid phosphatase level reached the control level at 28 days. At the close of the experiment (42 days), both serum calcium and acid phosphatase levels were again decreased. Calcitonin-induced hypocalcaemia resulted in hypertrophy of calcitonin cells which were densely packed with secretory granules up to day 21 of the treatment. Thereafter they displayed both hypertrophy and hyperplasia till the end of the experiment. Some calcitonin cells showed degranulation after 35 and 42 days of treatment. Few lead-haematoxylin-positive calcitonin cells with collapsed membranes and pyknotic nuclei were also seen in the lumina of the thyroid follicles toweards the close of the experiment. Parathyroid chief cells showed hypertrophy from 21 to 35 days of the treatment. From day 28 to the close of the experiment they released their secretory product. After 42 days of experimental treatment a growth-promoting effect of calcitonin was observed (increase in body weight and femur weight.