Circulating leptin levels are modulated by fasting, cold exposure and insulin administration in lean but not Zucker (fa/fa) rats as measured by ELISA

The development of a sensitive enzyme-linked immunosorbent assay (ELISA) is described for the quantitation of plasma leptin levels in both mice and mts. Approximately 1.5ng leptin/ml plasma was detected in lean mice but significantly (p<0.01) less was found in the plasma of ob/ob mice. In lean Zucker rats leptin circulated at approximately 4ng/ml plasma whereas levels were elevated more than 6-fold in fa/fa rats. Circulating leptin levels declined (p<0.05) in lean rats which were fasted or exposed to 4 degrees C for 24h, but subsequently recovered to normal within 12h of refeeding or warming, respectively. Administration of insulin increased leptin levels in lean rats within 3h (p<0.01). However, leptin levels were unchanged in fa/fa rats exposed to the same physiological stimuli. (C) 1996 Academic Press, Inc.