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Clonidine has some role in the treatment of spasticity, acting principally by inhibiting excessive sensory transmission below the level of injury [clarify]. Its use, however, is mainly as a second or third line agent, due to side effects such as hypotension, bradycardia, and drowsiness. [42]
The alpha-2 (α2) adrenergic receptor (or adrenoceptor) is a G protein-coupled receptor (GPCR) associated with the G i heterotrimeric G-protein. It consists of three highly homologous subtypes, including α 2A -, α 2B -, and α 2C -adrenergic. Some species other than humans express a fourth α 2D -adrenergic receptor as well. [1]
Alpha-adrenergic agonist. Alpha-adrenergic agonists are a class of sympathomimetic agents that selectively stimulates alpha adrenergic receptors. The alpha-adrenergic receptor has two subclasses α 1 and α 2. Alpha 2 receptors are associated with sympatholytic properties. Alpha-adrenergic agonists have the opposite function of alpha blockers.
First-dose phenomenon. The first-dose phenomenon is a sudden and severe fall in blood pressure that can occur when changing from a lying to a standing position the first time that an alpha blocker drug is used [1] or when resuming the drug after many months off. [2] This postural hypotension usually happens shortly after the first dose is ...
Alpha blockers work by blocking the effect of nerves in the sympathetic nervous system. This is done by binding to the alpha receptors in smooth muscle or blood vessels. [37] α-blockers can bind both reversibly and irreversibly. [2] There are several α receptors throughout the body where these drugs can bind.
Alpha-1 blocker. Alpha-1 blockers (also called alpha-adrenergic blocking agents or alpha-1 antagonists) constitute a variety of drugs that block the effect of catecholamines on alpha-1-adrenergic receptors. They are mainly used to treat benign prostatic hyperplasia (BPH), hypertension and post-traumatic stress disorder. [1]
Imidazoline receptors are the primary receptors on which clonidine and other imidazolines act. [1] [2] [3] There are three main classes of imidazoline receptor: I 1 is involved in inhibition of the sympathetic nervous system to lower blood pressure, [4] I 2 has as yet uncertain functions but is implicated in several psychiatric conditions, [5] [6] and I 3 regulates insulin secretion.
Pheochromocytoma is a rare tumor of the adrenal medulla composed of chromaffin cells and is part of the paraganglioma (PGL) family of tumors, being defined as an intra-adrenal PGL . [ 2 ][ 4 ][ 5 ] These neuroendocrine tumors can be sympathetic, where they release catecholamines into the bloodstream which cause the most common symptoms ...