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β-Adrenergic receptor antagonists (β-blockers) are medications used in the treatment of various cardiovascular, neurologic, endocrine, ophthalmologic, and psychiatric disorders. Among all the exposures to cardiovascular agents, β-blocker exposures were the leading cause of poison center calls and ranked among the top three in this class as a cause of severe toxicity and mortality.1
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The β-adrenergic receptors are membrane glycoproteins present as three subtypes in various tissues (Table 194-1). These receptors play a critical role in cardiovascular physiology by modulating cardiac activity and vascular tone.
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During times of stress (i.e., catecholamine release), β-adrenergic receptor stimulation increases myocardial and vascular smooth muscle cell activity through a sequence of intracellular events (Figure 194-1).2,3
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The β-receptor is coupled to a stimulatory Gs protein. This Gs protein stimulates adenylate cyclase, which in turn catalyzes the formation of cyclic adenosine monophosphate, the so-called intracellular second messenger. Increased cyclic adenosine monophosphate ultimately phosphorylates the L-type calcium channel, which leads to channel opening and calcium entry into the cell. Extracellular calcium is then coupled to the ryanodine receptor to carry the calcium current to the sarcoplasmic reticulum, which then releases its stored calcium. This process is termed calcium-induced calcium ...