Beta1 and beta2 receptor mechanisms in rat jugular veins: Differences between norepinephrine and isoproterenol-induced relaxation

The rat jugular vein possesses both beta1 and beta2 adrenergic receptors based on the use of two beta1 antagonists, practolol and atenolol and two beta2 antagonists, butoxamine and N-isopropylmethoxamine. In this vessel, norepinephrine and nylidrin interact primarily with beta1 receptors whereas isoproterenol and salbutamol interact with both beta1 and beta2 receptors showing a slight preference for beta2 receptors. Isoxsuprine-induced relaxation was not blocked by either beta1 or beta2 antagonists. Selectivity of norepinephrine for beta1 receptors and of isoproterenol for beta2 receptors also occurred in circular preparations of the portal vein after alpha adrenergic blockade. However, after alpha adrenergic blockade in rat aorta, practolol and N-isopropylmethoxamine were equieffective as antagonists of relaxation to norepinephrine and isoproterenol although N-isopropylmethoxamine was somewhat more effective than practolol.