Análises em amostras de saliva de ratos Wistar machos: ácido úrico, glutationa reduzida e corticosterona em diferentes idades

Abstract

Saliva is an aqueous fluid composed of a mixture of organic and inorganic components that has the following functions: lubrication and protection of the oral cavity; buffering activity and cleaning; maintenance of the integrity of the teeth; antimicrobial and immunological activity; starch digestion and taste perception. Its synthesis is carried out by the parotid, submandibular and sublingual glands and is controlled by the autonomic nervous system, with significant parasympathetic action. Most organic compounds are synthesized locally, while others reach the saliva from the blood. Salivary evaluation is used in humans to investigate markers for the diagnosis of local and systemic diseases. In rodents, the literature is scarce regarding the evaluation of salivary markers and the correlation with plasma. Our aim was to standardize saliva collection in male Wistar rats at 3 different ages and measure uric acid, reduced glutathione (GSH) and corticosterone. Animals provided from 15 litters (45 animals) were randomly chosen to be sacrificed at the following ages: 35 days (Group 35; n = 15); 60 days (Group 60; n = 15) and 90 days (Group 90; n = 15). To standardize saliva collection, tests were performed with the administration of pilocarpine in different doses to reach an effective and safe concentration. The animal was anesthetized with xylazine (5 mg/kg bw) and ketamine (20 mg/kg bw) and then pilocarpine (1.25 mg/kg bw + dilution with 200% saline by volume) was administered. After the fall of the 1st drop of saliva, the procedure was maintained for 15 minutes, and the sample was centrifuged. Uric acid, reduced glutathione and corticosterone were measured in the animals' saliva and plasma. Salivary uric acid concentration in group 60 was 82% higher than group 35 (p = 0.0057, mean difference = -0.2321) and plasma uric acid concentration in group 90 was 46% lower than group 60 (p = 0.0119, mean difference = -1.088). Salivary GSH concentration of group 60 was lower than that of groups 35 and 90 (56% , p = 0.0264, mean difference = 2.206; 59%, p = 0.0101, mean difference = -2.522, respectively), in plasma was 65% lower in group 60 than in group 35 (p = 0.0075, mean difference = 4.128). Salivary corticosterone was 81% and 84% lower in group 60 and 90 compared to group 35, respectively (p<0.0001, mean difference = 5.512; p<0.0001, mean difference = 5.657, respectively), in plasma it was 92% higher in group 90 compared to group 60 (p = 0.0010, mean difference = 203.3). A correlation between salivary uric acid and corticosterone in group 60 was observed. Here, we developed a minimally invasive protocol for saliva collection in eutrophic rats of different ages, allowing further studies to investigate the salivary profile, not only in healthy animals, but also in experimental models of different metabolic alterations.