Abstract
This study was performed to investigate whether or not α-adrenergic stimulation exerts a chronotropic effect on the heart. Isolated right atria of rats were used. Phenylephrine (10-5-10-4 mol/l), an a-agonist, did not affect the rate of the atrial beat under treatment with propranolol (1 x 10-6 mol/l), a β-blocker. When the atrial rate was increased to approximately double by treatment with isoproterenol (1 x 10-8 mol/l) or forskolin (1 x 10-6 mol/l), phenylephrine at the same doses significantly reduced the rate by about 6%. This effect was blocked by phentolamine (1 x 10-6 mol/l). These results suggest that α-adrenoceptors function to reduce heart rate in the atria, of which rate is raised through intracellular cAMP activity.
