| Objectives and methods: Blood pressure is sodium-sensitive in the majority of patients with non-insulin-dependent diabetes mellitus (NIDDM), in about 40% of patients with essential hypertension (EHT), and even in the (normotensive) children of subjects with EHT. Insulin resistance appears linked to sodium sensitivity. The aim of this project is to investigate whether sodium sensitivity of blood pressure is related to an impaired homeostatic response to insulin-induced renal sodium retention in patients with EHT and in healthy normotensive volunteers with high and low insulin sensitivity. Results: - Studies were performed in normal subjects (n=20), representing a wide range of insulin sensitivity, and in salt sensitive and salt resistant patients with essential hypertension (n=20). In contrast to our hypothesis, we found a positive correlation between insulin sensitivity and salt sensitivity in normal subjects. Insulin sensitivity did not differ between salt sensitive and salt resistant patients with essential hypertension. - Insulin infusion, both in physiological and supraphysiological dosages, increased renal plasma flow and glomerular filtration rate in normal subjects and hypertensives. Insulin also decreased fractional sodium excretion and increased distal tubular sodium reabsorption in both groups. - In the normal subjects, we found a positive correlation between insulin sensitivity and insulin-mediated changes in renal plasma flow and glomerular filtration rate during physiological hyperinsulinemia. Insulin sensitivity did not correlate with insulin-mediated changes in fractional sodium excretion. However, salt sensitivity showed a positive correlation with insulin-mediated changes in proximal tubular sodium reabsorption. - In the hypertensives, the effects of insulin on renal hemodynamics and sodium handling did not differ between the salt sensitive and the salt resistant group, although the salt sensitive hypertensives tended to retain more sodium in the course of the insulin infusion. - To conclude, our results do not support an association between insulin resistance and salt sensitivity. The relevance of the relationship between insulin sensitivity and insulin-mediated renal vasodilatation for blood pressure regulation remains to be determined. It also remains to be proven whether chronic hyperinsulinemia causes excessive sodium retention and salt sensitivity in humans. |
