Hirudin (desulfated, 54-65) contracts canine coronary arteries: Extracellular calcium influx mediates hirudin-induced contractions

Objective Although the anticoagulatory properties of hirudin are well known, its direct vasoactive effects have not been investigated extensively. Hirudin stimulates nitric oxide and prostacyclin production in noncoronary vascular beds, but its actions on coronary arteries are unknown. Materials and methods Five-millimeter segments of canine left circumflex coronary arteries were obtained for organ chamber experiments. Some segments were denuded of endothelium before study. Segments were exposed to hirudin (10 ^-10-10^-6 mol/L) following precontraction with prostaglandin F_2α with or without pretreatment with indomethacin or calcium channel blockers (verapamil and nifedipine). Results Hirudin stimulated endothelium-independent contraction in coronary arterial segments. Maximum tension (hirudin 10^-6 mol/L) above precontraction baseline was 33.6 ± 9.0% (n = 10, P < 0.05) for endothelium-intact and 31.8 ± 11.5% (n = 8, P < 0.05) for endothelium-denuded arterial segments. Differences between endothelium-intact and endothelium-denuded segments were not significant. Contractile responses to hirudin were unaffected by the presence of indomethacin. Pretreatment with either verapamil or nifedipine (10^-4 mol/L) for 1 h attenuated these contractions. The maximal increase in tension above baseline (hirudin 10^-6 mol/L) for verapamil and nifedipine was only 6.2 ± 12.4 and 3.8 ± 7.0% (n = 6, P < 0.05 versus endothelium-intact control), respectively. Conclusions Hirudin stimulates endothelium-independent contractions of canine coronary arteries in vitro. Pretreatment with calcium channel blockers attenuates this response, suggesting that extracellular influx of calcium has an important mechanistic role in hirudin-mediated coronary artery constriction.