Effect of salt-loading on blood pressure, insulin sensitivity and limb blood flow in normal subjects.
1. The aim of this study was to determine the effects of high (220 mmol/day) and low (40 mmol/day) salt intake for 6 days on blood pressure, leg blood flow and insulin sensitivity in 18 healthy normotensive subjects. 2. Twenty-four-hour ambulatory blood pressure was measured at baseline, during salt-loading and salt-depletion. Insulin sensitivity was determined by a two-step euglycaemic-hyperinsulinaemic clamp (low and high insulin infusion rates: 40 and 600 m-unit.min-1.m-2 respectively) and leg blood flow by plethysmography. 3. Salt-loading resulted in changes in weight [change between salt-loading and salt-restriction: delta=+0.45 (S.D. +/-0.69) kg, P=0.015], plasma renin [delta=-11.5 (S.D.+/-12.9) micro-units/l, P=0.001] and urinary noradrenaline [delta=-8.6 (S.D. +/-18.7) nmol/mmol creatinine, P=0.05]. There were borderline significant increases in 24-h systolic blood pressure [delta=+5.8 (S. D.+/-14.2) mmHg, P=0.06] and plasma volume [delta=+0.29 (S.D.+/-0. 67) litres, P=0.08]. 4. Insulin sensitivity was similar in both salt states. Geometric mean metabolic clearance rate of low-dose insulin: low salt, 5.13 (S.D.x//1.35) dl/min; high salt, 4.94 (S.D.x//1.37) dl/min, P=1.0. Geometric mean metabolic clearance rate of high-dose insulin: low salt, 9.68 dl/min (S.D.x//1.30); high salt, 9.68 (S.D. x//1.27) dl/min, P=0.69. 5. Leg blood flow response to high-dose insulin on high salt increased significantly compared with low salt. Percentage change of blood flow on low salt, delta=+36.6 (S.D.+/-22. 9)% versus high salt, delta=+66.8 (S.D.+/-52.2)%, P=0.03. 6. There were no significant relationships between salt-related changes in limb blood flow and changes in insulin sensitivity at either insulin infusion rate. 7. We conclude that salt-loading, despite changing body weight, the renin-angiotensin-aldosterone system, urinary noradrenaline and the leg blood flow response to insulin, has no significant effect on insulin sensitivity. Salt-loading causes dissociated effects on insulin-induced vasodilatation and glucose disposal.
Centre for Diabetes and Cardiovascular Risk, Department of Medicine, Whittington Hospital, University College London Medical School, G Block, Archway Wing, Archway Road, London N19 3UA, U.K.
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Foo
A E
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Denver
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Coppack
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JS
Yudkin
D000450:Aldosterone / Q000097:blood; D001794:Blood Pressure / Q000187:drug effects*; D018660:Blood Pressure Monitoring, Ambulatory; D001835:Body Weight; D003404:Creatinine / Q000652:urine; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D015309:Glucose Clamp Technique; D006801:Humans; D007328:Insulin; D007866:Leg / Q000098:blood supply*; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000652:urine; D010953:Plasma Volume / Q000187:drug effects; D010991:Plethysmography; D012039:Regional Blood Flow / Q000187:drug effects; D012083:Renin / Q000097:blood; D017673:Sodium Chloride, Dietary / Q000008:administration & dosage*
D007328:Insulin; D017673:Sodium Chloride, Dietary; D000450:Aldosterone; D003404:Creatinine; D012083:Renin; D009638:Norepinephrine