Beta-Blockers: Function and Effects

Catecholamines such as epinephrine and norepinephrine are key players within the endocrine system that are stimulated in response to the “fight or flight” reaction.  When stimulated, these hormones are rapidly released to bring about many physiological changes within the body. Physiologically, epinephrine and norepinephrine bind to adrenergic receptors found in various tissue target sites within the body- specifically in this case, the myocardial tissue of the heart causing a cascade of events. The cascade of events include vasoconstriction of the blood vessels due to increased cardiac output causing strain on the heart and vasculature. However, keep in mind that these effects can vary among target tissues due to the different adrenergic receptors located within each tissue area.

Fig. 1 shows the interaction between the beta-blocker, epinephrine, norepinephrine, and adrenergic receptors. The beta-blockers compete with the catecholamines to block the adrenergic binding sites on the myocardial tissue- thus inhibiting or alleviating muscle contraction, high blood pressure, and increased cardiac output.

Beta blockers…a wonder-drug?

With the increased incidence of abnormal heart rhythms, hypertension, and heart attacks; a catergory of drugs known as beta-blockers have emerged within the pharmaceutical industry to act as preventative and relief measures for these diagnosed health issues. This specific class of drugs work to block the binding sites for epinephrine and norepinephrine on the adrenergic receptors (β1 and β2) found primarily on myocardial tissue- although they have other uses. By blocking the binding sites of these catecholamines, the overall effect is leads to reduced heart rate, along with increased vasodilation of blood vessels resulting in a lowering of blood pressure (see link for more information).

After learning about the stress response on a hormonal level, I became curious regarding efficiency of beta-blockers and how they bring about change in one type of target tissue versus another. Do these drugs have higher affinity for receptors in a specific target tissue? Or is their functionality strictly in terms of concentration? Are there any side-effects one should be aware of that could indicate harmful effects elsewhere in the body after usage?

Varied results.

A recent study in Circulation Research, addresses the specificity of beta-blockers and their varied results. According to the study, beta-blockers should be approached with caution and considered heavily before deciding upon treatment. After analysis of heart therapy combinations, researchers discovered that each beta-blocker has completely different outcomes based on which type of recepor is its target. With the alpha- and beta- receptors as targets, there seems to be an overall benefit to the patient. In contrast, those that target solely the beta- receptors seem to be detrimental in the long run because the heart becomes accustomed to being a more efficient pump but wears out in a shorter amount of time. Other data are congruent with the prior findings, stating that beta-blockers can be selective or non-selective. Non-selective beta-blockers affect all of the systems that epinephrine and norepinephrine interact with normally including the heart, lungs, and blood vessels. Selective on the other hand, involves a very specific target tissue only allowing for a narrow range of effects. Beta-blockers also have side-effects involving the nervous, digestive, and muscular system.

In conclusion, beta-blockers are beneficial and yet sometimes harmful depending on the specificity, severity of the symptoms, and other therapy combinations involved. Beta-blockers have made huge strides for the medical/pharmaceutical field, but ongoing research is necessary to evaluate the entirety of interactions within the body to ensure proper use and full understanding for the future of biomedical research.