Increase of norepinephrine-induced endothelium-dependent relaxation of pulmonary artery in rats after chronic exposure to cold.

The present study was designed to determine whether norepinephrine (NE) mediate endothelium-dependent relaxations in arteries of the pulmonary vasculature of cold-acclimated rats. Twenty male Sprague-Dawley rats comprising two groups (Cold-acclimated for 12 weeks at 6°C, CA; Warm-acclimated for 12 weeks at 24 °C, WA) were used. After anesthesia, the pulmonary artery (4 mm long) was isolated. Pulmonary artery with and without endothelium were suspended for isometric force measurements in a buffered salt solution. The doseresponse relations for the vascular responses to the isolated pulmonary artery to norepinephrine (NE), phenylephrine (PE) and acetylcholine (Ach) were determined and compared in the CA group and the WA group. In the CA group, the vascular sensitivities to NE and PE-induced contraction in the pulmonary artery was significantly lowered than that in the WA group. NE and PE-induced contractions were significandy greater in endotheliumdenuded compared with endothelium-intact arteries. These differences of contraction responses to NE and PE between arteries with widiout endothelium were significantly greater in the CA group than in the WA group. There was no significant difference between the pulmonary arterial response to Ach in the CA group and that in the WA group. Our data suggest that chronic exposure to cold show decreased NE and PE-induced contraction responses in isolated pulmonary arteries and may decrease NE-induced contraction responses due to enhancing NE-induced endodielium derived relaxing factor release via up-regulating endothelial α-adrenoceptors.