Chronic salt overload increases blood pressure and improves glucose metabolism without changing insulin sensitivity.

ABSTRACT

The effect of sodium chloride salt restriction and overload on insulin sensitivity is still an open question. Some authors have shown that NaCl salt restriction increases insulin resistance, whereas others have reported the opposite. In the present study, the objective was to get some more insight on this issue by studying the influence of dietary salt content on glucose uptake in isolated adipocytes. Male Wistar rats were fed from weaning either low (0.15%) or high (7.94%) salt diets. On the 12th week of age, weight and tail-cuff blood pressure were measured, followed 10 days later by an intravenous glucose tolerance test with concomitant insulin determinations. One week later, the rats were killed by decapitation and epididymal adipocytes were obtained for glucose metabolism evaluation. No weight differences were observed between both groups of animals. Blood pressure was significantly higher (P < .001) on salt overloaded rats (146 +/- 11 mm Hg) than on salt restricted ones (115 +/- 5 mm Hg). Dietary salt content did not influence the area under the curve of plasma glucose. Area under the curve of insulin levels was lower (P = .023) on the high than on the low salt diet. A higher (P < .001) glucose uptake in the absence and in the presence of insulin was observed in adipocytes from rats on the high salt diet. The median effective concentration (EC50) from the dose-response curves of glucose uptake was the same on both groups of animals. Glucose oxidation and incorporation into lipids was also enhanced by salt overload. High salt increased insulin receptor density (P < .001). In conclusion, salt overload increased blood pressure, and high and low salt dietary content did not influence insulin sensitivity based on the unchanged EC50 from the in vitro studies. However, insulin-independent glucose uptake, oxidation, and incorporation into lipids were enhanced in adipocytes from rats on the high salt diet. The lower levels of insulin during the glucose tolerance test on salt-loaded animals may be a consequence of the higher insulin-independent glucose uptake in that group.