Increased insulin resistance in salt sensitive essential hypertension

Objective: To determine the possible relationship between insulin resistanc e and salt sensitivity in essential hypertension. Design and methods: We studied 17 non-obese, essential hypertensive patient s (24-h blood pressure: 149 +/- 15/94 +/- 5 mm Hg) with normal glucose tole rance. Salt sensitivity was diagnosed in the presence of a significant incr ease (P < 0.05, more than 4 mm Hg) in 24-h mean blood pressure (MBP) when p atients switched from a low-salt intake (50 mmol/day of Na+) to a high-salt intake (240 mmol/day of Na+), each period lasting 7 days. The insulin sens itivity index was determined by the euglycaemic hyperinsulinaemic clamp. Results: Six patients were classified as salt sensitive (24-h MBP increase: 6.2 +/- 1.1 mm Hg), and 11 as salt resistant (24-h MBP increase: -1.2 +/- 3.8 mm Hg), No significant differences were observed between salt sensitive and salt resistant patients regarding baseline characteristics, fasting se rum insulin, fasting serum glucose, glycosilated haemoglobin, total cholest erol, HDL-cholesterol, LDL-cholesterol, triglycerides, uric acid and microa lbuminuria, Salt sensitive patients exhibited a reduced insulin sensitivity index compared with salt resistant patients (1.7 +/- 1.1 vs 3.5 +/- 1.2 mg /kg/min; P = 0.009), An inverse relationship (r -0.57; P = 0.016) between t he insulin sensitivity index and 24-h MBP increase with high salt intake wa s found. Conclusion: Salt sensitive essential hypertensive patients are more insulin resistant than salt resistant patients when both salt sensitivity and insu lin resistance are accurately measured. Indirect measures of both insulin a nd salt sensitivity and/or the presence of modifying factors, such as obesi ty or glucose intolerance, may account for differences in previous studies.