Effects of beta 1- and beta 2-adrenoceptor stimulation on hemodynamics in the anesthetized rat

The role of beta 1-adrenoceptors in mediation of vasodilatation is not clear. The microsphere technique was used to compare the effects of mixed beta-, beta 1-, and beta 2-stimulation on blood flow and conductance changes in five groups of pentobarbital-anesthetized rats: I, vehicle; II, mixed beta-stimulation; III, beta 1-stimulation; IV, beta 2-stimulation; and V, mixed beta-blockade. Isoproterenol (32 ng/kg/min) was infused into rats either without (group II) or with ICI 118,551 (beta 2-blocker, 30 micrograms/kg, group III), atenolol (beta 1-blocker, 100 micrograms/kg, group IV), or both blockers (group V), respectively. At the doses selected, ICI 118,551 shifted the dose-vasodepressor response curve of salbutamol (beta 2-agonist) to the right but had no effect on the dose-chronotropic response curve of dobutamine (beta 1-agonist), whereas atenolol shifted the dose-chronotropic response curve of dobutamine to the right and had no effect on the dose-vasodepressor response curve of salbutamol. The results show that isoproterenol increased heart rate (HR) and arterial conductances in the coronary and skeletal muscle beds but had no effects in other beds. Combined with ICI 118,551, isoproterenol caused similar increases in HR and coronary arterial conductance but markedly less increase in skeletal muscle conductance. Atenolol abolished the increase in HR by isoproterenol but did not affect the increases in coronary and muscular arterial conductances. With both blockers, isoproterenol produced no increase in coronary and skeletal muscle conductance. Therefore, both beta 1- and beta 2-adrenoceptors play a role in coronary and skeletal muscle vasodilatation.(ABSTRACT TRUNCATED AT 250 WORDS)