Salt sensitivity is associated with insulin resistance in essential hypertension

The relationship between salt sensitivity and insulin resistance was investigated in nondiabetic, nonobese (body mass index less than or equal to 28) untreated patients with uncomplicated, mild-to-moderate essential hypertension. Alterations in insulin-mediated glucose disposal were assessed by means of the insulin suppression test. Subjects were classified as salt sensitive and salt resistant according to their blood pressure response to low and high salt intake. Fasting serum glucose levels were within normal limits and did not differ between salt sensitive and salt resistant hypertensives, irrespectively of the level of salt intake. Fasting serum insulin levels increased in salt sensitive patients when on a high intake of salt. The insulin suppression test revealed the existence of marked differences in insulin-mediated glucose uptake between salt sensitive and salt resistant hypertensives. Much higher steady-state glucose values (nanomoles of glucose/ liter) were obtained during the insulin suppression test in salt sensitive than in salt-resistant hypertensives (7.4 +/- 1.6 v 3.5 +/- 0.1 under low salt; and 12.5 +/- 1.1 v 4.3 +/- 0.1 under high salt intake). The product of glucose times insulin obtained at steady state during low and high salt intakes were 2.5 and 5 times greater, respectively, in salt sensitive than in salt resistant hypertensives. Therefore, the impairment in insulin-mediated glucose disposal observed in salt sensitive hypertensives was present both under low salt (60 to 70 mEq/day) and high salt intake (300 mEq/day). However, it was exacerbated under high salt intake. These results suggest that untreated salt sensitive hypertensives have a considerable impairment in insulin-mediated glucose disposal because of a state of insulin resistance. High salt intake increased BP, induced hyperinsulinemia, and worsened insulin-mediated glucose disposal only in salt sensitive patients. We propose that salt sensitivity contributes, separately from hypertension, to insulin resistance and thus be considered per se as an additional risk factor in the development of cardiovascular disease. Salt sensitivity and insulin resistance may be genetically associated conditions. (C) 1998 American Journal of Hypertension, Ltd.