SHORT-TERM HYPERTHYROIDISM HAS NO EFFECT ON LEPTIN LEVELS IN MAN

Leptin, a 16-kDa adipocyte-derived protein whose circulating levels re flect energy stores, increases the resting metabolic rate and thermoge nesis in rodents. Thyroid hormones also increase the basal metabolic r ate, but nothing is known about possible interactions between leptin a nd thyroid hormone. Activation of beta-adrenergic receptors decreases leptin levels in rodents. To test the hypothesis that thyroid hormones , by causing a ''functional hyperadrenergic'' state, result in decreas ed leptin concentrations in humans, we studied 22 normal healthy men b efore and after the administration of T-3 for 1 week to induce moderat e hyperthyroidism. Short term thyroid hormone excess does not alter ci rculating leptin concentrations despite a demonstrated effect on heart rate, systolic blood pressure, cholesterol levels, and metabolic inde xes of bone turnover. Elucidation of the apparently separate pathways by which thyroid hormones, beta-agonists, and leptin regulate energy e xpenditure and food intake may have important implications for our und erstanding of the mechanisms for regulating energy homeostasis in heal th and disease.