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Sodium–lithium countertransport is increased in normoalbuminuric type 1 diabetes but is not related to other risk factors for microangiopathy
Author(s) -
Vervoort G.,
Elving L. D.,
Wetzels J. F. M.,
Lutterman J. A.,
Smits P.,
De Pont J. J. H. H. M.,
Berden J. H. M.
Publication year - 2002
Publication title -
european journal of clinical investigation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.164
H-Index - 107
eISSN - 1365-2362
pISSN - 0014-2972
DOI - 10.1046/j.1365-2362.2002.00942.x
Subject(s) - medicine , microangiopathy , endocrinology , diabetes mellitus , diabetic nephropathy , blood pressure , renal function , endothelial dysfunction , albumin , chemistry
Background It has been reported that sodium–lithium countertransport (Na/Li CT) activity is increased in patients with diabetes mellitus and that this increased Na/Li CT activity is associated with the development of diabetic nephropathy. It is unclear however, whether Na/Li CT is related to other pathophysiological factors in diabetic patients. We studied kinetic parameters of Na/Li CT activity together with other putative risk factors for microangiopathy in normoalbuminuric type 1 diabetic patients and matched control subjects. Subjects and methods We measured maximum velocity ( V max ) and sodium affinity ( K m ) of Na/Li CT in 53 diabetic patients and 45 healthy controls. Endothelial function was assessed by monitoring forearm vascular response to intrabrachial infusion of acetylcholine. Blood samples were collected for measurement of HbA1c, glucose, insulin and lipids. Blood pressure was measured intra‐arterially. Renal haemodynamics were measured by inulin/ p ‐aminohippurate clearance. Urinary albumin was measured by enzyme‐linked immunosorbent assay. Transcapillary escape of albumin (TERalb) was calculated by the disappearance curve of 125 I‐labelled albumin. Results Vmax was increased in diabetic patients (779 ± 36 µmol Li + h −1 L −1 erythrocytes vs. 623 ± 35 in controls, P < 0·01), whereas K m was decreased (64 ± 16 mmol L −1 vs. 76 ± 27 in controls, P = 0·03). The ratio of V max : K m was 12·4 ± 0·6 in diabetic patients and 8·9 ± 0·9 in controls ( P < 0·001). When comparing diabetic patients in the lowest and highest quartile of V max or K m there were no differences in blood pressure, renal haemodynamics, urinary albumin excretion, TERalb, endothelial function, HbA1c, glucose, insulin, or lipid profile. Conclusion Na/Li CT is increased in uncomplicated type 1 diabetes and characterized by an increase in V max and a decrease in K m . The increase in Na/Li CT is not associated with changes in endothelial function, degree of metabolic control, blood pressure or renal haemodynamics.