Effects of sitagliptin on plasma incretin concentrations after glucose administration through an esophagostomy tube or feeding in healthy cats

We investigated the effect of sitagliptin, a dipeptidyl peptidase 4 inhibitor, on plasma incretin concentrations after glucose administration through an esophagostomy tube or feeding in healthy cats. Six cats were used for the glucose administration experiment and 5 cats were used for the feeding experiment. Glucose administration through an esophagostomy tube increased plasma glucagon-like peptide 1 (GLP-1) concentrations by 6-fold, whereas plasma glucose-dependent insulinotropic polypeptide (GIP) concentrations did not change. Feeding increased both plasma GLP-1 concentrations by 1.5-fold and GIP concentrations by 4.6-fold. Sitagliptin was administered through an esophagostomy tube (25 and 50 mg per cat) in the glucose administration experiment and orally (25 mg per cat) in the feeding experiment. Sitagliptin treatment potentiated the GLP-1 response to glucose by 1.5-fold (P < 0.05). In addition, postprandial plasma GLP-1 concentration was higher by 2-fold when sitagliptin was administered (P < 0.05). In contrast, administration of sitagliptin did not affect plasma GIP concentrations after glucose administration or feeding. Sitagliptin enhanced insulin secretion following glucose administration by 1.5-fold (P < 0.05); however, it did not influence the plasma glucose concentration. Furthermore, sitagliptin had no effect on the postprandial plasma glucose and insulin concentrations. In conclusion, this study provides no evidence that sitagliptin is beneficial for management of feline diabetes mellitus.

Natural anti-insulin autoantibodies in cats: enzyme-linked immunosorbent assay for the determination of plasma anti-insulin IgG and its concentrations in domestic cats

Anti-insulin immunoglobulin G (IgG) has been found in the sera of healthy cats. To determine the concentrations of these antibodies, an enzyme-linked immunosorbent assay (ELISA) for anti-insulin IgG was developed. ELISA maintained the linearity of a standard concentration line between 67.5 and 2160 ng/ml. The coefficients of variances (CVs) of intra-assays in two different plasma samples were 4.0% and 3.7%, respectively. The inter-assay CVs in two different plasma samples were 5.1% and 6.9%, respectively. The dilution curves of two samples were rectilinear. Anti-insulin IgG was detected in all 84 of the healthy cats that were tested. Plasma anti-insulin IgG concentrations ranged from 80 to 1578 μg/ml, with a median concentration of 221 μg/ml, and this value correlated positively with total plasma IgG concentrations (r=0.383, p<0.01). In an intravenous glucose tolerance test, plasma anti-insulin IgG concentrations did not alter, even with changes in plasma glucose and insulin concentrations. The ELISA that was developed was able to determine plasma anti-insulin IgG in domestic cats, and confirmed that all healthy cats had plasma anti-insulin IgG. Determining the plasma concentrations of anti-insulin IgG in cats with various pathological conditions might clarify the role of anti-insulin IgG.

Impact of commercially available diabetic prescription diets on short-term postprandial serum glucose, insulin, triglyceride and free fatty acid concentrations of obese cats

Diet therapy is an important treatment component available for obese cats. In this study, the impact of four commercially available prescription diet regimens (1 for general use and 3 aimed at treating obesity and diabetes mellitus (DM)) on short-term postprandial serum glucose, insulin, triglyceride and nonesterified fatty acid (NEFA) concentrations was investigated with five obese cats. The diet regimens used were as follows: C/D dry (general use: moderate protein, moderate fat, high carbohydrate and low fiber), M/D dry (DM: high protein, high fat, low carbohydrate and high fiber), W/D dry (DM: high protein, low fat, high carbohydrate and high fiber) and Diabetic dry (DM: high protein, low fat, low carbohydrate and high fiber). A significant reduction (10-13%) in postprandial glucose (area under the curve; AUC) was observed with the M/D and Diabetic diets, which both contained lower concentrations of carbohydrates than the C/D diet. An accompanying significant reduction (30-36%) in postprandial insulin AUC was also observed with the three DM diets, which all had higher amounts of fiber, as compared with the C/D diet. Lastly, a significant increase (32-65%) in postprandial NEFA AUC was observed with the M/D and Diabetic diets as compared with the C/D diet. Therefore, dietary amounts of carbohydrates and fiber, as opposed to protein content or dietary fat, appear to have a very significant impact on postprandial glycemia and subsequent insulin requirement levels in obese cats. In addition, dietary amounts of carbohydrates may also impact lipid metabolism in obese cats.