INSULIN, SODIUM-LITHIUM COUNTERTRANSPORT, AND MICROALBUMINURIA IN HYPERTENSIVE PATIENTS

Both microalbuminuria (>0.290 nmol/min [20 mu g/min]) and high sodium- lithium countertransport (SLC) in diabetic or hypertensive humans are predictive of overt nephropathy and more aggressive cardiovascular com plications, perhaps induced by insulin resistance. To analyze the rela tionships between microalbuminuria, SLC, microalbuminuria, and insulin in essential hypertension, we studied 90 hypertensive white patients, 25 of whom had microalbuminuria and 32 of whom were healthy. When uri ne sampling was completed for albuminuria determination, SLC was measu red; all patients then underwent standard (75 g) oral glucose load to measure basal (0 minutes) and 2-hour glucose and insulin serum levels. Glucose-insulin ratio was used as insulin sensitivity index (ISI). In both hypertensive patients with normal microalbuminuria and those wit h pathological microalbuminuria, plasma insulin at 120 minutes was sig nificantly higher than in control subjects. When the patients with pat hological microalbuminuria were divided into thirds on the basis of th eir microalbuminuria, in the lower third, we found statistically signi ficant less fasting insulin and higher basal ISI. SLC was higher in hy pertensives than normotensives and, among hypertensives, higher in the subgroup with elevated microalbuminuria. In hypertensives, we found a weak but significant correlation between SLC and microalbuminuria, in dependent of insulin or ISI. The prevalence of high value of SLC (grea ter than or equal to 0.383 mmol.L-1.h(-1)) was significantly lower in hypertensives with normal rather than abnormal urinary albumin excreti on. Our results indicate that in nondiabetic hypertensive whites, high er microalbuminuria is accompanied by signs of insulin resistance; mor eover, a link exists between SLC and microalbuminuria, both predictive of aggressive complications of hypertension.