Expression of leptin and beta 3-adrenergic receptors in rat adipose tissue in altered thyroid states

The level of leptin [the obese (ob) gene product] mRNA is markedly elevated in hypothyroid male rats. The administration of tri-iodothyronine (T3) to hypothyroid rats resulted in a 40% decrease in leptin mRNA at 8 h. This decrease in leptin mRNA was associated with a parallel decline in circulating leptin levels of about 50% at 24 h. Conversely, beta 3-adrenergic receptor mRNA levels were markedly decreased in epididymal adipose tissue from hypothyroid rats. T3 administration resulted in a 147% increase at 12 h in beta 3-adrenergic receptor mRNA. There was a corresponding increase due to T3 in the lipolytic response to the specific beta 3-adrenergic agonist CL 316,243 that paralleled the increase in beta 3-adrenergic receptor mRNA. T3-mediated changes in leptin and beta 3-adrenergic receptor mRNAs were blocked by cycloheximide, suggesting the involvement of short-lived proteins in these effects. The present results indicate that T3 has opposite effects to those of insulin on the white adipose tissue of rats with respect to leptin mRNA expression.