Glucose, insulin, and insulin resistance as biochemical predictors of hypertension

Circulating levels of endothelin-1 during acute hyperinsulinemia in patients with essential hypertension treated with type 1 angiotensin receptor antagonist or placebo

Insulin and angiotensin II (Ang II) are involved in the regulation of endothelin-1 (ET-1). This study investigates their possible influence on plasma levels of ET-1 in humans. Twenty patients with essential hypertension were included in a randomized, double-blind, placebo-controlled crossover study of 4 weeks' treatment with losartan, a selective type 1 angiotensin (AT1) receptor antagonist. The effect was evaluated in the fasting state and during acute hyperinsulinemia physiologically induced by oral glucose ingestion (OGTT) and by euglycemic glucose clamp. Losartan lowered blood pressure significantly, but did not influence plasma levels of ET-1 in the fasting condition (5.2 +/- 0.2 fmol/mL on placebo and 5.6 +/- 0.3 fmol/mL after losartan treatment). During both models of acute hyperinsulinemia, there was a significant decrease in plasma ET-1. In the OGTT the mean values after placebo treatment decreased from 5.2 +/- 0.2 fmol/mL at time 0 to 4.7 +/- 0.4 (P = .001) and 4.0 +/- 0.5 (P = .001) at 60 and 120 minutes, respectively. During the clamp the mean ET-1 values decreased from 5.7 +/- 0.4 fmol/mL at time 0 to 4.6 +/- 0.2 (P < .001) and 4.3 +/- 0.3 (P = .006) at 60 and 120 minutes, respectively. No differences in these profiles occurred after losartan treatment. Significant inverse correlation between fasting levels of ET-1 and insulin sensitivity index was found, r = -.51, P = .003. In conclusion, losartan did not influence the circulating levels of ET-1 in basal condition or during acute hyperinsulinemia, whereas a significant decrease in plasma ET-1 occurred during acute hyperinsulinemia. A significant inverse correlation demonstrated between basal levels of plasma ET-1 and the insulin-stimulated glucose uptake could point to a possible regulatory influence of ET-1 production on glucose metabolism or vice versa.

Insulin modulates circulating endothelin-1 levels in humans

Recent data indicate that insulin stimulates synthesis of the vasoconstrictor peptide endothelin-1 (ET-1) by cultured vascular endothelial cells in vitro. To determine whether insulin modulates ET levels in vivo and whether this effect is important in the pathogenesis of obesity-associated hypertension, we measured circulating immunoreactive ET-1 levels during euglycemic hyperinsulinemic clamps (20 mU/m2.min-1 for 120 minutes) in eight obese women (body mass index, 36 +/- 1 kg/m2) before and after 10 weeks on an 800-kcal/d protein-sparing liquid diet. During the clamp that preceded weight loss, insulin levels were increased from 17 +/- 2 to 51 +/- 3 mU/L and this was associated with an increment in ET-1 level from 28 +/- 3 to 33 +/- 3 pg/mL (P < .05). After weight loss, insulin levels were increased from 10 +/- 2 to 47 +/- 3 mU/L during the clamp, and there was a corresponding increase in ET-1 levels from 24 +/- 3 to 30 +/- 3 pg/mL (P < .025). The reduction in basal ET-1 level (from 28 +/- 3 to 24 +/- 3 pg/mL) with weight loss correlated strongly with the reduction in fasting immunoreactive insulin level (from 17 +/- 2 to 10 +/- 2 mU/L; r = .92, P < .01). The decrease in blood pressure with weight loss (from 130 +/- 6/73 +/- 3 to 118 +/- 4/72 +/- 3 mm Hg) did not correlate with the corresponding reduction in circulating ET-1 levels. These results indicate that insulin modulates ET-1 levels in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)