PLASMA LEPTIN TURNOVER RATES IN LEAN AND OBESE ZUCKER RATS

Conscious female adult lean and obese Zucker rats were injected throug h the jugular vein with radioactive iodine-labeled murine leptin; in t he ensuing 8 min, four blood samples were sequentially extracted from the carotid artery. The samples were used in a modified RIA for leptin , in which paired tubes received the same amount of either labeled or unlabeled leptin, thus allowing us to estimate both leptin levels and specific radioactivity. The data were used to determine the decay curv e parameters from which the half-life of leptin (5.46 +/- 0.23 min for lean rats and 6.99 +/- 0.75 min for obese rats) as well as the size o f its circulating pool (32 pmol/kg for lean rats and 267 pmol/kg for o bese rats) and the overall degradation rate (96 fkat/kg for lean rats and 645 fkat/kg for obese rats) were estimated. These Values are consi stent with the hormonal role of leptin and the need for speedy changes in its levels in response to metabolic challenge.