Labetolol; a combined b-adrenoceptor blocker that also
blocks a-adrenoceptors. Ordinary b-adrenoceptor blockers
are unsuitable for producing a quick antihypertensive effect
because a quick fall in blood pressure triggers a
compensatory sympathetic discharge that increases the
peripheral vascular resistance via a-adrenoceptors. Blocking
the b-adrenoceptors alone cannot prevent this
compensatory response, but the addition of an a-adrenoceptor
blocker can. It is this action that renders labetolol
suitable for gaining quick control of the blood pressure.
Labetolol, like all b-adrenoceptors, is contraindicated in
women with a history of asthma.