Aims/hypothesis  

This study was done to measure the effect of Na⁺ intake on blood pressure and albuminuria, in relation with insulin sensitivity and kidney haemodynamics, in Type 2 diabetic patients with and without microalbuminuria.

Methods  

Type 2 diabetic patients, 20 with microalbuminuria, 21 without, spent two consecutive 7-day periods, one on a high (250 mmol), the other on a low-Na⁺ (20 mmol) diet. Body weight, 24-h blood pressure and albuminuria were measured at the end of each period. At the end of high-Na⁺ diet insulin sensitivity (euglycaemic insulin clamp; 2 mU·kg^–1·min^–1) and kidney haemodynamics were measured in nine patients from each group.

Results  

Switching from low to high-Na⁺ diet resulted in an increase in blood pressure (7.4±4.7 mmHg; p<0.001), body weight (1.9±0.4 kg; p<0.05) and albuminuria [from 80 (31–183) µg/min to 101 (27–965) µg/min; p<0.01) in patients with microalbuminuria. No changes occurred in patients without microalbuminuria. Patients with microalbuminuria also had greater intraglomerular pressure (44±1 mmHg vs 36±1; p<0.001), calculated from glomerular filtration rate, renal plasma flow, plasma protein concentration and the relationship between pressure and natriuresis. In these patients insulin sensitivity was lower (5.16±49 vs 7.36±0.63 mg·kg^–1·min^–1; p=0.007). Urinary albumin excretion (r=0.40; p=0.009) and insulin sensitivity (r=–0.59; p=0.01) were correlated with intraglomerular pressure.

Conclusion/interpretation  

High salt intake increases blood pressure and albuminuria in Type 2 diabetic patients with microalbuminuria. These responses are associated with insulin resistance and increased glomerular pressure. Insulin resistance could contribute to greater salt sensitivity, increased glomerular pressure and albuminuria.