Insulin and blood pressure responses to changes in salt intake

In this study we evaluated the role of insulin in hypertension and on salt sensitivity. The study was conducted in 47 consecutive patients attending the Center for the Detection and Treatment of Cardiovascular and Metabolic Risk factors. The relationships between fasting and post-glucose load insulin levels and the blood pressure (BP) responses to changes in salt intake, were investigated. No correlation was observed between fasting or 2-h post-load insulin levels and mean BP (MBP), systolic BP (SBP) or diastolic BP (DBP). The plasma concentrations of insulin were not significantly related to body mass index (BMI) (r2 = 0.05; P = 0.135). Neither fasting nor 2-h post-load insulin predicted the BP response to changes in salt intake. A reduction in salt intake from 316 +/- 13 to 26 PM 3 mmoles/day, produced similar BP lowering in subjects with fasting insulin >15 microU/ml and in subjects with normal fasting insulin levels (<15 microU/ml). In addition, no relationship was observed between the magnitude of the BP responses to salt and the levels of insulin, either fasting (r2 = 0.007; P = 0.86) or 2-h after a glucose load (r2 = 0.01; P = 0.213). A very strong association was found between body weight or BMI and MBP (r2 = 0.443; P< 0.0001). In conclusion, our results are against the view of a cause-effect relationship between insulin and BP levels. In addition, the insulin status of a patient does not predict (nor determines) his (her) vascular reactivity to changes in salt intake. Finally, our findings further support the existence of a strong and direct association between body weight and hypertension, and speak against a major role of insulin in the pathogenesis of hypertension associated with obesity.