Effects of endothelin on the portal vein from spontaneously hypertensive and Wistar Kyoto rats.

The effects of endothelin, a novel potent vasoconstrictor peptide, on isolated portal veins were examined in spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). Endothelin contarcted the portal vein from SHR and WKY, in a concentration-dependent manner. However, both twitch contraction and tonic contraction of portal veins in response to endothelin were significantly enhanced in SHR. In contrast to the effects of endothelin, twitch contractile responses to Bay K 8644 were not significantly different between vessels from SHR and WKY. These results indicate that endothelin is a potent vasoconstrictor peptide in the portal vein, and that the increased sensitivity in SHR may be due to an increase in the activity of voltage-dependent Ca2+ channels which is modulated by endothelin, but not to an increase in the activity of voltage-dependent Ca2+ channels which can be stimulated by Bay K 8644.