Responsiveness of isolated thoracic aorta to norepinephrine and acetylcholine in cold-acclimated rats.

We investigated the responses of thoracic aortae to adrenergic contraction and endothelium-dependent relaxation following chronic exposure to cold in rats. Two groups (CA, cold-acclimated for 12 weeks at 5 °C; WA, warm-acclimated for 12 weeks at 24 °C) of 10 male Sprague-Dawley rats were used. After anesthesia, the thoracic aortae (4 mm long) were isolated and the vascular tension was measured with a force transducer. The dose-response relations for aortic responses to norepinephrine (NE), phenylephrine (PE) and acetylcholine (Ach) were determined and compared between the CA and the WA groups. In the CA rats, the thoracic aortae became more sensitive to Ach-induced vasorelaxation. The vascular sensitivities to NE- or PE-induced contraction in the thoracic aortae were lowered. Chronic exposure to cold decreased NE- and PE-induced vasoconstrictive responses and increased Achinduced vasorelaxative response of the isolated thoracic aortae, which were suggested to be due to enhanced release of NE-induced endothelium-derived relaxing factor by up-regulating endothelial α1-adrenoceptors.