1Adrenergic

1adrenergic, commonly referred to as alpha-adrenergic, denotes a subset of adrenergic receptors that respond to catecholamines. The primary subtypes are alpha-1 and alpha-2. Alpha-1 receptors are typically located postsynaptically on vascular smooth muscle and cause vasoconstriction when activated through Gq proteins, leading to increased intracellular calcium. Alpha-2 receptors are mainly presynaptic and inhibit norepinephrine release via Gi/o signaling, though they are also found postsynaptically in various tissues, including the central nervous system and platelets.

Endogenous ligands norepinephrine and epinephrine activate both alpha-1 and alpha-2 receptors, contributing to physiological effects such as increased peripheral resistance and blood pressure (via alpha-1) and feedback inhibition of norepinephrine release (via alpha-2). Pharmacologically, alpha-1 agonists like phenylephrine act as vasopressors and decongestants; alpha-1 antagonists like prazosin are used to treat hypertension and, in some cases, benign prostatic hyperplasia. Alpha-2 agonists such as clonidine and brimonidine reduce sympathetic outflow and are used in hypertension management and glaucoma, respectively. Alpha-2 antagonists like yohimbine can increase sympathetic activity.

Clinical relevance includes regulation of blood pressure, nasal congestion control, and ocular pressure management. Side effects associated with manipulating alpha-adrenergic receptors can include hypertension, reflex tachycardia, orthostatic hypotension, dry mouth, and, with central effects, sedation or confusion depending on the agent and site of action.

Note: If the term 1adrenergic is intended to refer to alpha-adrenergic receptors, standard nomenclature categorizes the subtypes as alpha-1 and alpha-2 with distinct signaling and clinical implications.