Thyroid Hormone Responses to Feeding in ob/ob Mice

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Abstract
Many of the disturbances which characterize adult C57BL/6 ob/ob mice, including obesity, hypometabolism and hypothermia could arise from reduced circulating levels of thyrotropin and thyroid hormones. In the present study, measurement of these hormones in ad libitum-fed obese and lean mice housed at 22 °C revealed that mutant mice had levels of TSH equal to those of their ?/+ siblings, while total T4 and T3 concentrations were slightly higher than those of lean controls. The hormonal responses of obese mice to overnight food deprivation or to meal ingestion were also similar to those of lean control mice. Males of both phenotypes typically had higher TSH, T4 and T3 concentrations than did females, and in male mice the circulating levels of each hormone were much more responsive to the feeding condition. The present data are consistent with recent reports of defective target tissue responses and impaired hormone deiodination rather than depressed pituitary-thyroid hormone levels in accounting for the metabolic disturbances which characterize ob/ob mice.