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.