Insulin sensitivity is associated with blood pressure response to sodium in older hypertensives. Dengel, Donald R., Robert V. Hogikyan, Michael D. Brown, Scott G. Glickman, and Mark A. Supiano. Department of Internal Medicine, Division of Geriatric Medicine, and GRECC, Ann Arbor Veterans Affairs Medical Center, Ann Arbor Michigan, 48105, National Institutes of Health Research Scientist Development Award in Aging KO1 AG0072301 (DRD), Department of Veterans Affairs Medical Research Service (MAS) and Geriatric Research, Education and Clinical Center (DRD, RVH, MAS) at Ann Arbor, University of Michigan, Claude D. Pepper Older Americans Independence Center (AG-08808 ), University of Michigan Clinical Research Center (RR-00042).
APStracts 4:0259E, 1997.
In some individuals an increase dietary sodium intake results in an increase in blood pressure. Increases in dietary sodium intake have also been reported to alter glucose metabolism in normotensive individuals. The purpose of this study was to determine if sodium resistant hypertensives are more insulin resistant and whether dietary sodium restriction improves insulin sensitivity in older, sedentary, overweight hypertensives. Insulin sensitivity was assessed by a frequently sampled intravenous glucose tolerance test to determine the insulin sensitivity index after one week of low (@20 mmol/L/d) and high (@200 mmol/L/d) sodium diets in twenty-one older (63+/-2 yrs), nondiabetic hypertensive individuals. Subjects were grouped on the basis of the difference in mean arterial blood pressure between diets (sodium sensitive: >5 mmHg increase in mean arterial blood pressure on high sodium n=14]; sodium resistant <5 mmHg increase in mean arterial blood pressure on the high sodium diet [n=7]). An analysis of variance on fasting plasma insulin levels indicated a significant (P=0.0002) group effect with the sodium sensitive individuals having lower fasting plasma insulin levels on the low (13+/-2 vs. 27+/-3 [mu]U/mL) and high (12+/-2 vs. 22+/-3 [mu]U/mL) sodium diets compared to the sodium resistant individuals. There was no dietary sodium effect on fasting plasma insulin levels. Similarly, there was a significant (P=0.0002) group effect in regards to insulin sensitivity indexes with the sodium sensitive individuals having significantly higher insulin sensitivity indexes on the low (3.26+/-0.60 vs. 0.91+/-0.31 x10-4/min/[mu]U/mL) and high (3.45+/ -0.51 vs. 1.01+/-0.30 x10-4/min/[mu]U/mL) sodium diets compared to the sodium resistant individuals. There was no effect of dietary sodium on insulin sensitivity index. There were significant positive correlations between the insulin sensitivity indexes on both the low and high sodium diet and the change in mean arterial blood pressure (r=0.45 and 0.56, each p<0.05). We conclude that sodium resistant individuals exhibit a greater degree of insulin resistance than sodium sensitive individuals and that dietary sodium restriction fails to improve insulin sensitivity regardless of sodium sensitivity status. 

Received 15 July 1997; accepted in final form 12 November 1997.
APS Manuscript Number E334-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 12 December 1997