Adrenergic receptors found in the periphery are alpha-1 (causing vasoconstriction) and beta-2 (vasodilatatory). Blocking of these beta-2 receptors without alpha blockage will lead to unopposed alpha-1 action, which leads to even further vasoconstriction.
Elevated blood pressure seen in essential hypertension is not due to highly elevated catecholamines. Therefore, even if beta-2 receptors are blocked, there won't be an aggravated alpha-1 activity. Pathophysiology of essential hypertension is thought to be related with Na+ retention. A drug like propranolol will block beta-1 receptors, which will decrease renin synthesis. Decreased renin synthesis will decrease the activity of renin-angiotensin-aldosterone system. Among other effects, decreased aldosterone will cause decreased Na+ absorption from collecting ducts.
