1. We have investigated whether local vascular production of nitric oxide or prostacyclin regulates venoconstriction induced by the endothelium-derived peptide, endothelin-1, in vivo in man.

2. Six healthy subjects received local dorsal hand vein infusion of endothelin-1 for 60 min alone or, on two separate occasions, co-infused with the donator of nitric oxide, glyceryl trinitrate, or the vasodilator prostaglandin, prostacyclin. In further studies, endothelin-l was co-infused with an inhibitor of nitric oxide production, NG-monomethyl-L-arginine, or after oral administration of the irreversible inhibitor of prostaglandin production, acetylsalicylic acid (aspirin).

3. At a low dose (5 pmol/min), endothelin-1 alone caused slowly developing and long-lasting venoconstriction (maximal constriction: 66 ± 4%). Although glyceryl trinitrate partially prevented endothelin-1-induced venoconstriction (maximum: 33 ± 5%), inhibition of nitric oxide production did not affect endothelin-1-induced venoconstriction (maximum: 55 ± 4%).

4. Prostacyclin was more effective at blocking the venoconstriction in response to endothelin-1 than glyceryl trinitrate (maximum: 12 ± 3%), and there was substantial potentiation of endothelin-1-induced venoconstriction after pretreatment with aspirin (maximum: 90 ± 3%).

5. Despite the capacity of nitric oxide to attenuate responses to endothelin-1, NG-monomethyl-L-arginine did not potentiate endothelin-1-induced venoconstriction, suggesting little or no stimulated production of nitric oxide in human veins. However, the potentiation of responses to endothelin-1 by aspirin indicates that endothelial production of prostacyclin attenuates responses to endothelin-1 in human veins in vivo.

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