A 3-year-old child has been ad

Methoxamine and phenylephrine are used as pressor agents intreating hypotension and shock. Oxymetazoline, tetrahydrozoline,xylometazoline and some preparations of phenylephrine are used asnasal decongestants.

Side effects of centrally acting α2-adrenoceptor agonistsinclude sedation, dry mouth and nasal mucosa, bradycardia (becauseof increased vagal stimulation of the SA node as well assympathetic withdrawal), orthostatic hypotension, and impotence.Constipation, nausea and gastric upset are also associated with thesympatholytic effects of these drugs. Fluid retention and edema isalso a problem with chronic therapy; therefore, concurrent therapywith a diuretic is necessary. Sudden discontinuation of clonidinecan lead to rebound hypertension, which results from excessivesympathetic activity.

When the alpha receptor isstimulated by epinephrine or norepinephrine, thearteries constrict. This increases the blood pressure and the bloodflow returning to the heart.

α1 receptor – bronchioles(although minor relative to the relaxing effect of β2receptor on bronchioles) blood vessels of ciliary body(stimulation causes mydriasis)

Actions of the α1 receptormainly involve smooth muscle contraction. It causesvasoconstriction in many bloodvessels,

Ansewer is Renin release dorm the kidneys (Causes asignificantly greater suppression of renin release inhibits reninrelease by activation of an intrarenal a-adrenergicreceptor.)