Beta-Receptor Activity in Aorta

Abstract

Helically cut thoracic aortic strips (from rats, rabbits, and guinea pigs) in a state of low to moderate tone and under the influence of alpha-receptor blockade relaxed in response to isoproterenol. Propranolol blocked these relaxations. Helically cut thoracic aortic strips from cats and abdominal aortic strips from rats, rabbits, and cats were not relaxed by isoproterenol. In addition, aortic beta-receptor activity of rats and rabbits decreased with increasing age. The ability of thoracic aortas to be relaxed by isoproterenol was lost when rats were 90 days old and when rabbits were 2 years old. Significant loss of beta-receptor activity was not evident in rat trachea and stomach. Sodium nitrite completely relaxed thoracic and abdominal aortas from all species including thoracic aortas from old rats and rabbits. We conclude: (1) there are species differences in the response of thoracic aortic strips to beta-receptor stimulation; (2) a gradient in beta-receptor activity exists in the aorta with greater activity in the thoracic aorta and a relatively small amount of activity in the abdominal aorta; and (3) aortic beta-receptor activity decreases with increasing age.