INSULIN SENSITIVITY IS ASSOCIATED WITH BLOOD-PRESSURE RESPONSE TO SODIUM IN OLDER HYPERTENSIVES

The purpose of this study was to determine whether sodium-resistant hy pertensives are more insulin resistant and whether dietary sodium rest riction improves insulin sensitivity in older hypertensives. Insulin s ensitivity was assessed by a frequently sampled intravenous glucose to lerance test to determine the insulin sensitivity index (S-I) after 1 wk each of low- (20 mmol.l(-1).day(-1)) and high- (200 mmol.l(-1).day( -1)) sodium diets in 21 older (63 +/- 2 yr) hypertensives. Subjects we re grouped on the difference in mean arterial blood pressure (MABP) be tween diets [sodium sensitive (SS): greater than or equal to 5-mmHg in crease in MABP on the high-sodium diet (n = 14); sodium resistant (SR) : < 5-mmHg increase in MABP on the high-sodium diet (n = 7)]. There wa s no dietary sodium effect on fasting plasma insulin or S-I. An analys is of variance indicated a significant (P = 0.0002) group effect, with SS individuals having lower fasting plasma insulins on the low- (13 /- 2 vs. 27 +/- 3 mu U/ml) and high- (12 +/- 2 vs. 22 +/- 3 mu U/ml) s odium diets compared with SR individuals. Similarly, there was a signi ficant (P = 0.0002) group effect in regard to S-I, with SS individuals having significantly higher S-I on the low- (3.26 +/- 0.60 vs. 0.91 /- 0.31 mu U x 10(-4).min(-1).ml(-1)) and high- (3.45 +/- 0.51 vs. 1.0 1 +/- 0.30 mu U x 10(-4).min(-1).ml(-1)) sodium diets compared with SR individuals. We conclude that SR individuals exhibit a greater degree of insulin resistance than SS individuals and that dietary sodium res triction fails to improve insulin sensitivity regardless of sodium sen sitivity status.