INSULIN STIMULATES ENDOTHELIN-1 SECRETION FROM HUMAN ENDOTHELIAL-CELLS AND MODULATES ITS CIRCULATING LEVELS IN-VIVO

Endothelin-1 (ET-1) is a potent vasoactive and mitogenic peptide produ ced by the vascular endothelium. In this study, we evaluated whether i nsulin stimulates ET-1 secretion by human endothelial cells derived fr om umbilical cord veins and by human permanent endothelial hybrid cell s Ea.hy 926. Moreover, to provide evidence that insulin may stimulate ET-1 secretion in vivo, plasma ET-1 levels were evaluated in 7 type II diabetic normotensive males (mean age, 54.3 +/- 4.0 yr) during 2-h hy perinsulinemic euglycemic clamps (287 pmol insulin/m(2) . min(-1)) as well as in 12 obese hypertensive males (mean age, 44.2 +/- 4.6 yr) bef ore and after a 12-week period of caloric restriction. Our results sho wed that insulin stimulated ET-1 release from cultured endothelial cel ls in a dose-dependent fashion. ET-1 release persisted for 24 h and wa s also observed at physiological insulin concentrations (10(-9) mol/L) . The insulin-induced ET-1 secretion was inhibited by genistein, a tyr osine kinase inhibitor, and by cycloheximide, a protein synthesis inhi bitor, suggesting that it requires de novo protein synthesis rather th an ET-1 release from intracellular stores. In the in vivo experiments, plasma ET-1 levels rapidly increased during euglycemic hyperinsulinem ic clamps (from 0.76 +/- 0.18 pg/mL at time zero to 1.65 +/- 0.21 pg/m L at 60 min; P < 0.05) and persisted elevated until the end of insulin infusion (1.37 +/- 0.37 pg/mL at 120 min; P < 0.05 vs. time zero). In obese hypertensives, plasma ET-1 levels significantly decreased after 12 weeks of caloric restriction (from 0.85 +/- 0.51 to 0.48 +/- 0.28 pg/mL; P < 0.04). The decrease in body weight induced by caloric restr iction was accompanied by a significant reduction in fasting insulin l evels (from 167.2 +/- 94.0 to 98.9 +/- 44.9 pmol/L; P < 0.05) which co rrelated with the reduction in plasma ET-1 levels (r = 0.78; P < 0.003 ). In conclusion, our data show that insulin stimulates both in vitro and in vivo ET-1 secretion. Such interaction could play a significant role in the development of atherosclerotic lesions in hyperinsulinemic conditions.