Salt sensitivity in young normotensive subjects is associated with a hyperinsulinemic response to oral glucose

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Insulin resistance associated with a hyperinsulinemic response to oral glucose intake has been found in patients with essential hypertension and is believed to play a role in inducing hypertension by causing renal sodium and water retention. We therefore examined whether salt-sensitive, young normotensives, assumed to be predisposed to essential hypertension, exhibit impaired glucose tolerance in a similar way. The plasma insulin and glucose response to oral glucose intake (75 g) was assessed in 23 healthy, lean, male volunteers ingesting either 20 mmol or 260 mmol NaCl/day for 6 days each in a single-blind randomized crossover study. Salt sensitivity was defined as a significant drop in mean arterial blood pressure greater than 3 mmHg (means of 30 readings in the supine subject; P < 0.05) under the low-salt diet. Following the glucose load, plasma levels of both glucose and insulin were significantly higher (P < 0.01) in the salt-sensitive (n = 10) compared with the salt-resistant subjects (n = 13) during the high-salt diet but not during the low-salt diet. Whereas in the salt-sensitive group glucose tolerance improved with dietary salt restriction (P < 0.01), it deteriorated in the salt-resistant group (P < 0.05). Following the glucose load under the high-salt diet, there was a significant drop in blood pressure in the salt-sensitive (P < 0.005) but not the salt-resistant subjects. The hyperglycemic and hyperinsulinemic response in salt-sensitive subjects suggests that insulin resistance is present in these subjects prior to the development of hypertension and that it can be ameliorated by salt restriction. Thus, hyperinsulinemia could play an important role in salt sensitivity and in the later development of high blood pressure in these individuals.

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