Alpha agonist has all of the following actions except: September 2009
Ans. C: General Anesthesia Alpha-adrenoceptor agonists bind to alpha-receptors on vascular smooth muscle and induce smooth contraction and vasoconstriction, thus mimicking the effects of sympathetic adrenergic nerve activation to the blood vessels. Vascular smooth muscle has two types of alpha-adrenoceptors: alphal and alpha2. The alphal-adrenoceptors are the predominant alpha-receptor located on vascular smooth muscle. Depending on the tissue and type of vessel, there are also alpha2-adrenoceptors found on the smooth muscle. There are also alpha2-adrenoceptors located on the sympathetic nerve terminals that inhibit the release of norepinephrine and therefore act as a feedback mechanism for modulating the release of norepinephrine. Alpha-agonists constrict both aeries and veins; however, the vasoconstrictor effect is more pronounced in the aerial resistance vessels (small aeries and aerioles). Alphal-adrenoceptor agonists (systemic vasoconstrictors) Methoxamine Phenylephrine Oxymetazoline Tetrahydralazine Xylometazoline Methoxamine and phenylephrine are used as pressor agents in treating hypotension and shock. Oxymetazoline, tetrahydralazine, xylometazoline and some preparations of phenylephrine are used as nasal decongestants. Alpha2-adrenoceptor agonists (centrally-acting vasodilators) Clonidine Guanabenz Guanfacine Alpha-methyldopa The alpha2-adrenoceptor agonists are used very occasionally as centrally-acting sympatholytic vasodilators for the treatment of hypeension.
Hypotension
Hypeension
General anesthesia
Nasal decongestant