LEPTIN DOES NOT FULLY ACCOUNT FOR THE SATIETY ACTIVITY OF ADIPOSE TISSUE-CONDITIONED MEDIUM

To determine whether leptin alone accounts for the satiety activity se creted by native adipose tissue, we prepared culture media conditioned by microdissected adipose tissue from overfed Long-Evans rats, fa/fa rats, or db/db mice (media A, B, and C, respectively). Medium A signif icantly suppressed food intake following intracerebroventricular deliv ery to Long-Evans rats (2-h chow intake = 68 +/- 5% of baseline, P < 0 .001). Media B and C significantly suppressed food intake following in traperitoneal delivery to ob/ob mice (24-h chow intake = 56 +/- 7% of baseline for medium B, P = 0.001; 4-day chow intake = 78 +/- 3% of bas eline for medium C, P = 0.004). Using a leptin receptor-based bioassay , we determined that the leptin concentration of medium C was 392 +/- .18 ng/ml. This concentration was 20-fold lower than the concentration of recombinant murine leptin required to produce a similar degree of feeding suppression following 5 days of administration to ob/ob mice. Neither medium conditioned by adipose tissue from ob/ob mice nor mediu m conditioned by adipose tissue from fa/fa rats and subsequently immun odepleted of leptin had significant satiety activity. We conclude that leptin is necessary but not sufficient to account for the satiety act ivity of native adipose tissue, perhaps due to the production by adipo cytes of a cofactor that augments the ability of leptin to suppress fe eding.