Effect of sodium intake on blood pressure and albuminuria in Type 2 diabetic patients: the role of insulin resistance.
OBJECTIVE
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) microg/min to 101 (27-965) microg/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.


CONCLUSIONS
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.
Vedovato
M
M
Unit for Metabolic Disease, Department of Clinical and Experimental Medicine, University of Padua, Padua, Italy.
Lepore
G
G
Coracina
A
A
Dodesini
A R
AR
Jori
E
E
Tiengo
A
A
Del Prato
S
S
Trevisan
R
R
D000419:Albuminuria / Q000378:metabolism*; D000450:Aldosterone / Q000097:blood; D001786:Blood Glucose / Q000378:metabolism; D001794:Blood Pressure / Q000187:drug effects*; D001835:Body Weight / Q000187:drug effects; D003924:Diabetes Mellitus, Type 2 / Q000503:physiopathology* / Q000652:urine; D004032:Diet; D004039:Diet, Sodium-Restricted; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology; D015309:Glucose Clamp Technique; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D007333:Insulin Resistance / Q000502:physiology*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D018579:Patient Selection; D011188:Potassium / Q000652:urine; D017595:Renal Plasma Flow / Q000502:physiology; D012083:Renin / Q000097:blood; D012709:Serum Albumin / Q000378:metabolism; D012964:Sodium / Q000008:administration & dosage / Q000494:pharmacology* / Q000652:urine
D001786:Blood Glucose; D007328:Insulin; D012709:Serum Albumin; D000450:Aldosterone; D012964:Sodium; D012083:Renin; D011188:Potassium