Contraction and relaxation responses of femoral artery and aorta to norepinephrine in young rats

Abstract

1. 1. In femoral artery of 3-week-old rats, norepinephrine (NE) at 1 nM-0.1 μM concentration-dependently produced a contraction but, at higher concentrations (0.3–30 μM), NE relaxed the tissue. 2. 2. In aorta of the 3-week-old rat, NE elicited a contraction at 1 nM to 0.3 μM and a relaxation at 1 μM and higher. 3. 3. The magnitude of the NE-induced relaxation in the aorta was much less than that in the femoral artery. 4. 4. Atenolol (a β 1-selective antagonist) modulated these NE responses in the femoral artery and butoxamine (a β 2-selective antagonist) in the aorta. 5. 5. Subcutaneous application of propranolol and isoproterenol for 10 days in 4-week-old rats sensitized and desensitized the NE-induced relaxation, respectively. 6. 6. It is suggested that, in the young rat, β 1-and β 2-adrenoceptors contribute the NE-induced relaxation in the femoral artery and aorta, respectively, and that β-adrenoceptors may contribute to the limitation of NE-induced vasoconstriction in certain types of vascular beds.