How are a2 agonists involved in vascular tone?

Used as primary tx of systemic HTA Clonidine (decrease NE from sympathetic NS, tx HTA resistant, preop sedation relief anxiety, transdermal patches for hot flashes post menopause, adverse effects are rebound HTA, dry mouth and sedation) Methyldopa (centrally acting antiHTA, imp for HTA w/renal insufficiency, used in pregnant, adverse effects dry mouth, sedation and drousiness)