α₁ adrenergic receptor agonists

α₁ adrenergic receptor agonists acts predominantly on α₁ adrenergic receptors of animals. here we will see pharmacological effects and pharmacology of these alpha-1 agonists.

Pharmacological effects of α₁ agonists

α₁ adrenergic receptor agonists produces peripheral vasoconstriction with resulting increase in BP and small decrease in COP.

Trough phenylephrine has no direct effect on myocardium, it produces reflex bradycardia. It decreases cutaneous, renal splanchnic blood flow, but increases the coronary blood flow. It causes mydriasis and reduces intraocular pressure.

Pharmacokinetics of α₁ adrenergic agonists

Given orally is rapidly metabolized in the GI tract and does not produce any response. Hence, given parenterally by IV or IM routes.

α₁ agonists is mainly metabolized in the liver and partly its action is terminated by uptake into tissue.

α₁ adrenergic agonists-

Phenylephrine

Phenylephrine is a direct acting non-catecholamine with powerful α₁ adrenergic agonistic activity. It has negligible β agonistic and CNS actions.

Chemically phenylephrine differs from adrenaline in lacking 4-OH group on the benzene ring. It is less potent than nor adrenaline on α₁, but has long duration of action.

Methoxamine

Methoxamine is a directly acting sympathomimmetic with relatively selective α receptor action. But unlike phenylephrine, methoxmine slightly higher doses has some β receptor blocking action. This β- receptor blocking effect makes it less prone to induce cardiac arrhythmias.

Methoxamine is primarily used in the treatment of hypotensive states. In contrast, to other adrenergic drugs, methoxamine can be used during general anesthesia with halogenated hydrocarbons.