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Objective To study the effect of the satiety hormone, leptin, in saliva proteome and salivary gland histology and ultrastructure. Design Increases in blood leptin levels were induced through mini-pump infusion in male Wistar rats, during a period of 7 days. Saliva was collected before and at the end of the experimental period, for proteomic analysis, and major salivary glands were collected, at the end, for biochemical, histological and ultrastructural analysis. Results Immunohistochemistry revealed the presence of leptin receptors in major salivary glands. Salivary amylase levels and enzymatic activity were decreased in saliva, whereas the enzymatic activity of this protein was increased in the cytosol of parotid gland cells. Transmission electron microscopy allowed the observation of high number of electron-dense granules in cytosol of parotid acinar cells, from leptin treated animals. Conclusions Increased levels of plasmatic leptin result in changes in saliva composition and salivary glands function. To our knowledge, this is the first study providing evidences for a potential role of leptin in salivary gland secretion and saliva composition. An understanding of how appetite/satiety factors influence saliva composition and how this composition influences food processing in mouth may be relevant in understanding ingestivebehaviour.

Salivary a-amylase, a major protein in saliva, has been described as a marker for sympathetic nervous system activity, hence for metabolic energy balance. In this context, its expression in overweight and obesity is of interest. Rats fed with a diet enriched with sunflower oil differentially gained weight yielding two subgroups according to their susceptibility (OP) or resistance (OR) to obesity. Elevated plasmatic levels of leptin in the OP subgroup and altered plasmatic lipid profiles (lower triglycerides and higher total choles- terol/HDL ratio compared to controls) in OR subgroup were observed. Animals from OP subgroup presented higher a-amylase expression and activity even prior to the dietary treatment, suggesting that this salivary protein may constitute a putative indicator of susceptibility for fat tissue accumulation. After 18 weeks of high-fat diet consumption, salivary a-amylase levels did not significantly changed in OP subgroup, but increased 3-fold in OR subgroup. The raise of a-amylase for the latter might represent an adaptation to lower starch intake. These results suggest that salivary a-amylase secretion might be useful to predict susceptibility for weight gain induced by high-fat diet consumption. This paper is funded by FEDER Funds through the Operational Programme for Competitiveness Factors-COMPETE and National Funds through FCT-Foundation for Science and Technology under the Strategic Projects PEst-C/AGR/UI01, PEst-OE/AGR/ UI0115/2014, 15/2011, PEst-C/SAU/LA0001/2011 and PEst-C/QUI/ UI0062/2011. Authors acknowledge also the financial support from the Portuguese Science Foundation (FCT) in the form of Post- Doctoral grant (SFRH/BPD/63240/2009) of Elsa Lamy. The Portu- guese Science Foundation (FCT) played no role in the develop- ment of the present work or upon its submission for publication.