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Response of rabbit ear artery to endothelin‐1 during cooling

1 The effects of cooling on the response of rabbit central ear artery to endothelin‐1 and the role of the endothelium in these effects were studied in 2 mm long cylindrical arterial segments. 2 Concentration‐response curves for endothelin‐1 (10−10–3 × 10−7 m) were recorded isometrically in arteries with and without endothelium at 37°C and during cooling (24°C). To analyze further the endothelial mechanisms of the response to endothelin‐1 during cooling, the effects of this peptide in the presence of NG‐nitro‐l‐arginine methyl ester (l‐NAME) (10−4 m) or meclofenamate (10−5 m) were also determined. 3 In every condition tested, endothelin‐1 produced a marked, concentration‐dependent arterial contraction. Sensitivity of intact arteries to this peptide was consistently lower at 24°C than at 37°C. At 37°C there were comparable responses of arteries with and without endothelium, but at 24°C arteries without endothelium showed a higher sensitivity than intact arteries to endothelin‐1. 4 l‐NAME (10−4 m) increased the maximal contraction at 37°C, and both the sensitivity and maximal contraction at 24°C of intact arteries to endothelin‐1. Meclofenamate (10−5 m) did not affect the arterial response to endothelin‐1. 5 Sensitivity of arteries with and without endothelium to nitroprusside (10−9–10−3 m) was significantly decreased during cooling, and endothelium removal did not affect the relaxation to this nitrovasodilator. 6 These results suggest that cooling decreases sensitivity of cutaneous arteries (ear artery) to endothelin‐1 probably by increasing the availability of endothelial nitric oxide.