Effect of thyroid hormone on concentrations of plasma calcitonin in broiler chicks

The purpose of these studies was to determine the effect of thyroidectomy ( Tx), and thyroid hormone (T-3/T-4) treatment on concentrations of plasma CT in chicks. In addition, the turnover of CT in Tx- and T-3/T-4-treated chic ks was estimated using a novel nonradioactive salmon CT preparation. One-we ek-old broiler chicks (Gallus domesticus) (n = 75) were divided into three groups. Group I was sham-injected daily (i.m. saline), Group II was injecte d with 50 mu g/day of T-3/T-4 while Group III was injected with the goitrog en, methimazole, (150 mg/kg BW per day) for 8 weeks. Chicks (8-9 weeks old) were implanted with catheters in the brachial wing vein and administered r uthenium-labeled salmon CT. Blood samples were collected at 30 s, 1, 2, 4, 8, 20 min, and 3 h after injection. Results showed that concentrations of p lasma CT were decreased in T-3/T-4-injected birds. There was no significant effect of methimazole on circulating concentrations of plasma CT. The half -life of CT was significantly increased (P < 0.05) in both T-3/T-4-injected (n = 6; 1.34 +/- 0.16 min) and goitrogen-treated birds (n = 2; 5.81 +/- 2. 83 min) compared to controls (n = 7; 54 +/- 3 s) The results demonstrate th at changes in concentrations of plasma thyroid hormones can significantly a ffect concentrations of plasma CT. (C) 1999 Elsevier Science Inc. All right s reserved.