EFFECT OF TRIIODOTHYRONINE ON LEPTIN RELEASE AND LEPTIN MESSENGER-RNAACCUMULATION IN RAT ADIPOSE-TISSUE

Leptin, the product of the obese gene, is produced by white adipocytes . The release of leptin, as well as leptin mRNA content, was enhanced in adipocytes isolated from hypothyroid rats. The administration of tr i-iodothyronine (T-3 ) 8 h before death inhibited leptin release by ad ipocytes incubated for 6 or 24 h. Direct addition of T-3 to pieces of adipose tissue enhanced the loss of leptin mRNA seen over 24 h in the presence of dexamethasone plus the beta(3)-adrenergic agonist Cl 316,2 43. In contrast, if pieces of adipose tissue were incubated with dexam ethasone plus insulin, enhanced the T-3 accumulation of leptin mRNA. T hese results indicate that T-3 enhances net adipocyte leptin mRNA accu mulation in a condition that approximates the fed state (presence of i nsulin) but inhibits leptin mRNA accumulation in a condition that appr oximates the fasted state (absence of insulin).