Identification of leptin in human saliva

Leptin is produced predominantly in adipose tissue but has recently also be en found in gastric mucosa. It has been shown that the oral application of leptin induces neuronal activity in the brain stem of rodents. The objectiv e of the present study was to identify this hormone in human saliva and to examine the production and stability of salivary leptin. We have demonstrat ed production of leptin in salivary glands and oral mucosa by RT-PCR, its s torage by immunocytochemistry, and the release of the peptide by RIA. Chrom atographic analysis and immunoblotting confirmed the identity of leptin. Th ere is a strong linear correlation (r(2) = 0.78) between leptin concentrati ons from simultaneously collected saliva and plasma samples (n = 61). Stimu lation of saliva flow increases total leptin secretion up to 3-fold (P < 0. 001). As to the stability of leptin in gastric fluid, we found the peptide was not degraded above pH 3.5. Additionally, salivary leptin remains stable up to 5 d at 4 C. With regard to the presence of leptin receptors in gastr ic mucosa, we suggest salivary leptin as being a possible ligand for gastri c leptin receptors. Furthermore, the determination of leptin in saliva allo ws for noninvasive sample collection.