Improvement and Initial In Vivo Application of the Radioimmunoassay of Rat Thyrocalcitonin12

Previously we reported a homologous radioimmunoassay for rat thyrocalcitonin (TCT) which was sensitive enough (2-3 ng/ml serum) to measure TCT in thyroid venous blood or thyroid gland extracts but could not detect TCT in peripheral blood even after provocative challenge with iv calcium. In the present study chicken antisera to rat TCT were developed which were sufficiently sensitive (120-240 pg/ml serum) to permit initial evaluation of changes in TCT in rat peripheral blood. The following results were observed: (1) Basal serum TCT in young male Holtzman rats was undetectable, being < 120-240 pg/ml; (2) induction of marked hypercalcemia by iv calcium increased TCT to ∼1000-3000 pg/ml within 5 min; (3) thyroid cautery increased TCT to ∼1000 pg/ml in 5-15 min; (4) calcium gavage (12.2 mg Ca/100 g) produced modest hypercalcemia in 30-60 min and increased serum TCT to ∼500 pg/ml; (5) injection of isoproterenol raised serum TCT detectably; (6) injection of large doses of gastrin or pentagastrin did not produce detectable increases in TCT 5 or 30 min later.The results show that suitable antisera to rat TCT can be developed in chickens and applied to the measurement, by radioimmunoassay, of elevated circulating levels of TCT in the rat.The authors wish to acknowledge advice from Drs. Paul L. Munson and Tai-Chan Peng, and technical assistance from Mrs. Deloris B. Alston and Mr. John R. Hagaman, Jr.