A patient with acute heart failure refractory to cardiac glycosides was given an injection of dobutamine. What is the mechanism of action of this drug?

Answer options

1. Inhibition of phosphodiesterase activity
2. Complexation with membrane phospholipids
3. Inhibition of K+, Na+- ATPase
4. Increase of n.vagus tonus
5. Stimulation of 3-1-adrenergic receptors