Functional Alteration in the Thyroid C Cells in Rats with Experimentally Induced Thyroid Disorders.

Effects of thyroid dysfunction on the secretory ability of thyroid C cells (parafollicular cells) were studied in rats.The rats born to mothers thyroidectomized on day 5 of gestation (Tx-F1) were found to have an increased serum thyroxine level and a decreased basal level of serum calcitonin.The calcitonin secretory response to gastrin related peptide (gastrin) was normal in these rats.Neonatal treatment of rats with 0.5 or 2 , tg of thyroxine from 2 to 10 days of age (neoT4) resulted in a marked hypothyroid state in adulthood.They showed a significant decrease in the basal serum calcitonin levels and in the calcitonin response to gastrin stimulation.The rats in both groups showed a significant retardation in the body growth and the growth retardation was much greater in the neoT4 rats than in the Tx-F1 rats.The results suggest that the thyroid function alone or together with the thyrotrope function in the pituitary during the fetal life and neonatal period in the rat is important for the functional development of thyroid C cells.