Heavier the substitution on amino radical, greater is the beta activity. Isopropyl or propyl substitution in isoprenaline basically acts only on the beta receptors.
Positive ionotropic effect, positive chronotropic effect, positive dromotropic effect and positive bathmotropic effect occurs. Thus the heart rate and contractility is increased. Beta 2 receptors stimulate vasodilatation in the skeletal muscles. Thus the systolic pressure is increased while the diastolic pressure is decreased, as a result of which the pulse pressure widens.
The cardiac output is increased as well.
Beta 2 receptors in bronchioles cause bronchodilatation.
Uses are declining as specific drugs for beta 1 and beta 2 receptors are available. Sometimes it can be used for
- Heart block –in which impulses fail to travel from SA node to the ventricles
- Bronchial Asthma
a. By bronchodilatation
b. Inhibition of release of mediators of inflammation from mast cells by beta 2 receptors.