SALT SENSITIVITY IS ASSOCIATED WITH INSULIN-RESISTANCE IN ESSENTIAL-HYPERTENSION

The relationship between salt sensitivity and insulin resistance was i nvestigated in nondiabetic, nonobese (body mass index less than or equ al to 28) untreated patients with uncomplicated, mild-to-moderate esse ntial hypertension. Alterations in insulin-mediated glucose disposal w ere assessed by means of the insulin suppression test. Subjects were c lassified as salt sensitive and salt resistant according to their bloo d pressure response to low and high salt intake. Fasting serum glucose levels were within normal limits and did not differ between salt sens itive 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 gluco se uptake between salt sensitive and salt resistant hypertensives. Muc h higher steady-state glucose values (nanomoles of glucose/ liter) wer e 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 s alt; and 12.5 +/- 1.1 v 4.3 +/- 0.1 under high salt intake). The produ ct of glucose times insulin obtained at steady state during low and hi gh salt intakes were 2.5 and 5 times greater, respectively, in salt se nsitive than in salt resistant hypertensives. Therefore, the impairmen t in insulin-mediated glucose disposal observed in salt sensitive hype rtensives 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 hypertens ives have a considerable impairment in insulin-mediated glucose dispos al because of a state of insulin resistance. High salt intake increase d BP, induced hyperinsulinemia, and worsened insulin-mediated glucose disposal only in salt sensitive patients. We propose that salt sensiti vity contributes, separately from hypertension, to insulin resistance and thus be considered per se as an additional risk factor in the deve lopment of cardiovascular disease. Salt sensitivity and insulin resist ance may be genetically associated conditions. (C) 1998 American Journ al of Hypertension, Ltd.