Hypothalamo-adenohypophyseal-thyroid interrelationships in the chick embryo: II. Effects of thiourea treatment of plasma total thyroxine levels and thyroidal 125I uptake

• Published in: General and comparative endocrinology Vol. 37; no. 2; pp. 167 - 176
• Main Authors: Thommes, Robert C., Tonetta, Sharon A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.02.1979
• Subjects: Animals; Chick Embryo; Hypothalamo-Hypophyseal System - physiology; Iodine - metabolism; Kinetics; Thiourea - pharmacology; Thyroid Gland - drug effects; Thyroid Gland - physiology; Thyroxine - blood
• ISSN: 0016-6480; 1095-6840
• DOI: 10.1016/0016-6480(79)90104-7

After thiourea administration to chick embryos on Day 5.5, total plasma thyroxine concentrations were significantly decreased on Days 7.5, 9.5, 10.5, and 11.5 of incubation. Also, radioiodide uptake in normal and thiourea-treated embryos was measured at 1.0, 3.0, and 5.0 hr post-treatment on all days studied. There was no statistically significant difference in radioiodide uptake between normal and goitrogen-treated embryos on Days 7.5 and 9.5. However, on Days 10.5 and 11.5, a statistically significant increase in radioiodide uptake was observed in thiourea-treated individuals as compared to nontreated embryos. Thyroid wet weights were compared between normal and thiourea-treated embryos on all days studied. There were no statistically significant differences in wet weights between normal and goitrogen-treated individuals on the days assayed. The data indicate that on Day 10.5 of incubation, the pituitary and/or hypothalamus of the chick embryo first responds to decreases in circulating T 4 levels. Thus, the maturation of the hypothalamo-adenohypophyseal-thyroid axis during Days 10.0–13.0 of development in the chick embryo may be similar to that found in sheep and humans at midgestation.