Abstract

Orien L Tulp*, O F Obidi, T C Oyesile, Frantz Sainvil, Rolando Branly, A Sciranka, Syed A A Rizvi, Aftab Awan, Michael Anderson and George P Einstein

To determine the potential for subclinical thyroidal actions as a contributing factor for hormonal regulation of energy balance and the development of obesity and metabolic syndrome, studies of resting and catecholamine stimulated metabolism, in vivo thyroid hormone half-life, thyroid hormone bind characteristics and weight gain, groups of lean and obese congenic LA/Ntul//-cp rats were offered stock or high energy diets and in vivo and in vitro parameters of thyroid hormone action determined. The obese phenotype demonstrated impaired thermic responses to diet and environment and cold induced thermoregulation, in association with decreases in plasma T3 but not T4 concentrations. The plasma half-life of T4 was ~50% longer in obese than in lean littermates, while the half-life of T3 was similar in both phenotypes. Measures of nuclear thyroid hormone receptor density were similar in both phenotypes, but receptor affinity for T3 was diminished in the obese phenotype, consistent with impaired thyroidal actions as a contributing factor for subclinical hypothyroidism in the obese phenotype of this strain.