Response of rabbit ear artery to endothelin‐1 during cooling

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Abstract
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. 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. 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. 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. 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. These results suggest that cooling decreases sensitivity of cutaneous arteries (ear artery) to endothelin‐1 probably by increasing the availability of endothelial nitric oxide.