Effects of low-dose heparin infusion on arterial endothelin-1 release in humans

Background The aim of this study was to evaluate the effect of low-dose heparin infusion on arterialized endothelin-1 (ET-1) release in the presence of fasting or high insulin levels in healthy humans. Methods and Results Eleven normal subjects underwent two tests in random order lasting 240 minutes. A primed (250 IU), continuous heparin (600 IU/h) infusion was performed in test 1, saline was infused in test 2 as control. At 120 minutes, a eugly cemic hyperinsulinemic clamp (25 mU . kg(-1). h(-1)) was started that lasted 7 hours in both tests. Two hours after heparin infusion (test 1), ET-1 levels decreased by 32% (3.52+/-0.60 to 3.02+/-0.73 pg/mL), while nitric oxide (NO) and forearm blood flow increased by 29% and 14%, respectively. During saline infusion, ET-1, nitric oxide, and forearm blood flow remained unchanged. There was a significant interaction between the effect of decreasing ET-1 levels and the heparin treatment (F, 4.06; df, 3.30; P<.01). The decrease in ET-1 levels was significantly correlated with the increase in forearm blood flow in test 1 (r=.74; P<.01) but not in test 2. During the heparin/insulin period, ET-1 increased by 25%, returning to fasting values; nitric oxide levels increased by 12%; and forearm blood how remained unchanged. Conclusions The present study showed that it is possible to decrease ET-1 levels by use of low-dose heparin infusion in humans. This effect seems mediated by a simultaneous increase in nitric oxide levels and is completely reversed by a mild increase in insulin concentrations.