Iodothyronine kinetics in the rabbit: an experimental model

• Published in: Journal of endocrinology Vol. 106; no. 1; pp. 87 - 94
• Main Authors: PEARCE, C. J, BYFIELD, P. G. H, VEALL, N, HIMSWORTH, R. L
• Format: Journal Article
• Language: English
• Published: Colchester BioScientifica 01.07.1985; Portland Press
• Subjects: Animals; Biological and medical sciences; Female; Fundamental and applied biological sciences. Psychology; Hormones. Regulation; Kinetics; Male; Rabbits; Radioimmunoassay - methods; Thyroid. Parathyroid. Ultimobranchial body; Thyroxine - blood; Triiodothyronine - blood; Triiodothyronine, Reverse - blood; Vertebrates: endocrinology; Vertebrata; Mammalia; Aminoacid derivative hormone; Thyroxine; Rabbit; Thyroid hormone; Triiodothyronine; Kinetics; Iodothyronine; Lagomorpha; Metabolism
• ISSN: 0022-0795; 1479-6805
• DOI: 10.1677/joe.0.1060087

ABSTRACT Turnover studies of thyroxine (T4), 3,5,3′-tri-iodothyronine (T3) and 3,3′,5′-tri-iodothyronine (rT3) have been performed in the rabbit. A novel modification of a conventional radioimmunoassay has been used to measure specific 125I-labelled iodothyronines in small volumes of plasma in the presence of other 125I-labelled metabolites. Kinetic analysis of plasma disappearance of tracer was performed by a new theoretical approach. For T4 the mean (±s.d.) plasma concentration, clearance and production rates were 34±12 nmol/l, 109±19 ml/kg per day and 3·7±1·4 nmol/kg per day respectively (n = 9). For T3 the corresponding values were 2·04±0·42 nmol/l, 1·52±0·29 litres/kg per day and 3·07±0·76 nmol/kg per day (n = 8), and for rT3 0·12±0·04 nmol/l, 5·7±1·7 litres/kg per day and 0·69±0·23 nmol/kg per day (n = 8). The combination of these two new methodologies affords a simple and convenient means of studying iodothyronine metabolism under normal and abnormal conditions. The techniques employed may be generally applied to turnover studies of other compounds of physiological interest which can be measured by radioimmunoassay. J. Endocr. (1985) 106, 87–94