A Adrenergic Receptor Antagonists

Effects of a adrenergic antagonists may be predicted from the consequences of a receptor stimulation. The a1 adrenergic receptors mediate contraction of arterial and venous smooth muscle. The a2 receptors are involved in suppressing sympathetic outflow from the CNS, increasing vagal tone, facilitating platelet aggregation, inhibiting the release of NE and ACh from nerve endings, and regulating metabolic effects (e.g., suppression of insulin secretion and inhibition of lipolysis) and contraction of some arteries and veins.

a receptor antagonists are chemically heterogeneous and have a wide spectrum of pharmacological specificities (Figure 10-3, Table 10-3). Prazosin is much more potent in blocking a1 than a2 receptors (i.e., a1 selective), whereas yohimbine is a2 selective; phentolamine has similar affinities for both of these receptor subtypes. Newer agents discriminate amongst the subtypes of a particular receptor (e.g., tamsulosin has higher potency at a1A than at a1B receptors). Table 10-3 summarizes the properties of three chemically distinct groups of a blockers.

• Phenoxybenzamine • Prazosin •Yohimbine

• Phentolamine • Terazosin

• Tamsulosin

• Penbutolol

• Propranolol

• Acebutolol

• Bisoprolol

• Metoprolol

■ Bucindolol

• Celiprolol

• Phenoxybenzamine • Prazosin •Yohimbine

• Phentolamine • Terazosin

• Tamsulosin

• Penbutolol

• Propranolol

• Acebutolol

• Bisoprolol

• Metoprolol

■ Bucindolol

• Celiprolol

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