ATC Group: C01CA Adrenergic and dopaminergic agents

Dobutamine is a synthetic, sympathomimetic amine, structurally related to isoproterenol and dopamine, and is administered as racemate. The positive inotropic effect is primarily based on the agonistic effect on cardiac beta1-receptors but also on cardiac alpha1-receptors.

Dopamine exerts positive inotropic and chronotropic effects on the myocardium, acting as an agonist at beta-adrenergic receptors. Depending on the vascular bed being studied and the dose administered, dopamine can cause relaxation or contraction of vascular smooth muscle.

Droxidopa is a synthetic amino acid analog that is directly metabolized to norepinephrine by dopa-decarboxylase, which is extensively distributed throughout the body. Droxidopa is believed to exert its pharmacological effects through norepinephrine and not through the parent molecule or other metabolites. The exact mechanism of action of droxidopa in the treatment of neurogenic orthostatic hypotension is unknown.

Ephedrine is a sympathomimetic amine acting directly on the alpha and beta receptors and indirectly by increasing the release of noradrenaline by the sympathetic nerve endings. As with any sympathomimetic agent, ephedrine stimulates the central nervous system, the cardiovascular system, the respiratory system, and the sphincters of the digestive and urinary systems.

Epinephrine is a direct acting sympathomimetic agent, which exerts effects on both α and β adrenoceptors. It has more pronounced effects on β than on α adrenoceptors, although α effects prevail at high doses. The effects of adrenaline include increased rate and force of cardiac contraction, cutaneous vasoconstriction and broncho-dilatation.

Etafedrine, a sympathomimetic agent that acts on the sympathetic receptors of the bronchial tree relaxing spasm in a manner similar to that of ephedrine, is a bronchodilator and a selective β2-adrenoreceptor agonist. Etafedrine also belongs to the family of medications called decongestants. It works by narrowing blood vessels in the nasal passages, helping to relieve nasal stuffiness.

Fenoldopam is a rapid-acting vasodilator. It is an agonist for D₁-like dopamine receptors and binds with moderate affinity to α₂-adrenoceptors. Fenoldopam may increase norepinephrine plasma concentration.

Isoprenaline is a potent non selective beta-adrenergic agonist with low affinity for alphaadrenergic receptors. Isoprenaline acts primarily on the heart and on smooth muscle of bronchi, skeletal muscle vasculature and the gastrointestinal tract.

Metaraminol is a potent sympathomimetic amine that increases both systolic and diastolic blood pressure, is an adrenergic receptor alpha-1 agonist. Metaraminol is indicated for prevention and treatment of the acute hypotensive state occurring with spinal anesthesia. It is also indicated as adjunctive treatment of hypotension due to hemorrhage, reactions to medications, surgical complications, and shock associated with brain damage due to trauma or tumor. Metaraminol is also used in the treatment of priapism, in spite of this application was not approved, it appears to be effective.

Midodrine is the rapidly absorbed pro-drug of the pharmacologically active constituent desglymidodrine. Desglymidodrine is a sympathicomimetic with a direct and selective effect on the peripheral α1-adrenergic receptors. This α1-stimulative effect induces vasoconstriction of the venous system.

Noradrenaline provides a strong stimulation of alpha receptors in blood vessels at which these are counter-extracted. Noradrenaline also has an effect on beta-1 receptors in the heart leading to a positive inotropic and initially positive chronotropic effect. The increase in blood pressure may cause a reflex reduction in heart rate.

Octopamine is an organic chemical closely related to norepinephrine. In many types of invertebrates it functions as a neurotransmitter. Octopamine is known to exert adrenergic effects in mammals although specific octopamine receptors have been cloned only in invertebrates. It has been shown that octopamine can stimulate alpha(2)-adrenoceptors (ARs) in Chinese hamster ovary cells transfected with human alpha(2)-ARs. Octopamine stimulates lipolysis through beta(3)-rather than beta(1)-or beta(2)-AR activation in white adipocytes from different mammalian species. Octopamine activates only beta(3)-ARs and is devoid of alpha(2)-adrenergic agonism. Thus, octopamine could be considered as an endogenous selective beta(3)-AR agonist. In humans Octopamine is a trace amine found endogenously in the human brain where it interacts with signalling of catecholamines; it is structurally similar to synephrine and tyramine, being a metabolite of the latter (via dopamine β-hydroxylase) and substrate for the synthesis of the former (via phenethanolamine N-methyltransferase³) while being perhaps the closest in structure to noradrenaline.

Phenylephrine is a sympathomimetic agent with mainly direct effects on adrenergic receptors. It has predominantly alpha adrenergic activity and is without stimulating effects on the central nervous system. The sympathomimetic effect of phenylephrine produces vasoconstriction which in turn relieves nasal congestion.