Figure 6. Vasoactive agents and their receptor distribution and action in various systems.

Dopamine is a precursor of norepinephrine. Norepinephrine is converted to epinephrine by Phenylethanolamine methyl transferase (PNMT). Dopamine has a dose-dependent effect on dopamine (D₁ and D₂) receptors, β₁ and α₁ receptors. Epinephrine is equally effective on β₁ and α₁ receptors. Norepinephrine predominantly acts on α₁ receptors causing systemic vasoconstriction. It is thought to stimulate α₂ receptors in pulmonary vascular endothelium and release NO leading to pulmonary vasodilation. Milrinone and levosimendan increases cardiac contractility. Vasopressin acts on V₁ receptors to induce systemic vasoconstriction, V₂ causing fluid retention in the kidneys and V₃ leading to pituitary stimulation to produce ACTH. Vasopressin also stimulates pulmonary vascular endothelial V₁ receptor and pulmonary vascular smooth muscle V₂ receptor to induce pulmonary vasodilation. Copyright Satyan Lakshminrusimha.