Hypertension Physiology and Medications

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Table of Contents

Abstract
Introduction
Mechanisms of Action
Beneficial Effects
Side Effects
Conclusions
References

Abstract

ACE Inhibitors and Angiotensin II receptor blockers are very important drugs in combating hypertension. In this paper, I delve into both of these drugs in detail. An analysis of their mechanisms is given whereby I explained that while ACE inhibitors and ARB’s were similar in terms of inhibiting the effect of angiotensin II, they differ in terms of the blockage of angiotensin II; the breakdown of bradykinin; and the suppression of angiotensin II levels during chronic treatment.

I also look into their beneficial effects, explaining what makes them highly effective. These included reducing heart attacks; strokes; kidney problems; reducing cholesterol build-up; and so on. I then contrast this with their side effects which are more common and severe for ACE inhibitors as compared to ARB’s. Some of these include coughing and angioedema in ACE inhibitors; headaches, dizziness, a runny nose, and muscle cramps in ARB’s. I round off the discussion with a conclusion of my findings. Overall, this provides a balanced and comprehensive analysis of two of the most important drug types in the field of hypertension.

Introduction

ACE Inhibitors are a class of very useful drugs that prevent the formation of the natural substances that are responsible for increasing blood pressure (“Glossary Cardiac Terminology”, 2007). These drugs assist in reducing the heart’s workload and also prevent heart muscle damage. They treat hypertension (or high blood pressure) and do this by controlling the behavior of angiotensin-converting enzymes or ACE (“Hypertension Dictionary”, 2008).

Examples of ACE Inhibitors are enalapril (Vasotec®), captopril (Capoten®), and lisinopril (Zestril®). Angiotensin II receptor blockers, on the other hand, are drugs that help lower blood pressure levels by interfering with the action of angiotensin II (“John Hopkins Hypertension”, 2007). They help blood vessels relax and widen and some examples are Avapro, Diovan, and Cozaar. Both these drugs have served in making the lives of hypertension patients a lot easier than in the past.

Mechanisms of Action

A mechanism of action basically refers to the mechanism through which a pharmacologically active substance produces an effect in a biochemical system or on a living organism (“Mechanism Of Action”, 2008).
Drugs work in varied ways in order to achieve the desired result (whether curative or preventive) and so do ACE Inhibitors and Angiotensin II receptor blockers.
Though these two drugs give more or less of the same results, their mechanisms of action are markedly different.
The similarity between the two is that both of them inhibit the effect of angiotensin II which then causes blood vessels to widen, reducing the workload of the heart and blood pressure (“Angiotensin II receptor”, 2008).
In addition, both ACE inhibitors and ARB’s intervene in the renin-angiotensin system (RAS) cascade. The difference is that ACE inhibitor action is more specific than that of ARB’s since they affect the final step of this cascade which is the binding of the angiotensin II to its receptor (“Mechanism Of Action”, 2007).
Moreover, they also differ in that ACE inhibitors work by lowering the levels of angiotensin II while Angiotensin II receptor blockers (ARB’s) prevent/ block angiotensin II substances from entering receptors in the blood vessels and smooth muscles of the heart. This is because, since angiotensin II can be formed by other enzymes apart from ACE such as chymase, blockade of angiotensin II at cellular receptors, therefore, represents a more precise and effective mechanism for inhibiting the renin-angiotensin system.
Another difference between the two is that while ACE inhibitors reduce the breakdown of bradykinin (potentiation), ARB’s have no such effect (“Mechanism Of Action”, 2007). Bradykinin is a protein that has a very powerful effect on the contraction of smooth muscles such as the heart. This probably explains why very few patients who receive ARB’s experience the “ACE inhibitor cough” as compared to 15- 20 percent of those patients treated ACE inhibitors.
In addition, angiotensin II levels do not remain suppressed during chronic treatment using an ACE inhibitor but instead increase towards the level they were at before treatment (“Mechanism Of Action”, 2007). This suppression is believed to be a result of bradykinin potentiation. ARB’s, on the other hand, block the AT1- receptor and increase plasma angiotensin II at the same time. This results in a situation whereby the AT1- receptor becomes blocked and the AT2- receptor becomes exposed to its agonist angiotensin II. This is quite beneficial and experimental studies show that stimulation of the AT2-receptor may produce anti-proliferative effects treatment (“Mechanism Of Action”, 2007).

Beneficial Effects

Both the ACE inhibitor and angiotensin II have immense benefits for patients beyond just treating hypertension. Medicine Net (2008) gives the following benefits:

ARB’s and ACE inhibitors both reduce heart attacks or myocardial infarction.
Both reduce strokes.
Both prevent the re-occurrence of cardiac arrest.
They both benefit the kidney by reducing proteinuria (loss of protein in the urine), slowing the progression of renal failure especially in diabetics, and also preserving renal (kidney) function.
They both promote greater health by fighting cholesterol build-up.
One difference is that ACE inhibitors have been found to have a therapeutic effect on patients which helps them relax and even recover more (“Therapeutic Benefits”, 2008). This has not been established in the case of ARB’s.

Side Effects

Despite these admittedly remarkable benefits, both ACE inhibitors and ARB’s have their slight weaknesses although side effects with ARB’s are rare and of lesser magnitude. According to the Joint Commission (2005), these side effects include:

ACE inhibitors often cause a dry, persistent cough while ARB’s do not. This occurs in one out of ten patients who use ACE inhibitors.
ACE inhibitors cause angioedema (an allergic reaction that is characterized by edema of the lips eyelids and certain mucosa or other parts of the body and facial swelling. It can prove to be especially dangerous when it affects the laryngeal or pharyngeal mucosa. The swelling then inhibits breathing and can also cause true asphyxia (“Patients and Public”, 2008).
ARB may cause lesser symptoms such as headaches, dizziness, a runny nose, and muscle cramps though this is quite rare.
A very small percentage of people do experience potentially serious side effects from ARB’s such as hyperkalemia, kidney impairment, and altered liver function (Weber, 2008).

Conclusions

In summary, it is evident that both ACE inhibitors and ARB’s are crucial in the treatment of hypertension. As discovered, these drugs do not only treat hypertension but also have extra benefits that make them especially attractive for usage. Overall, ARB’s are better since they have fewer side effects. However, they are more expensive than ACE inhibitors which may prevent many potential users from using them.

References

About Hypertension. 2008. Hypertension dictionary. Web.

Atacand. 2007. Mechanisms of action. Web.

John Hopkins Health Alerts. 2007. Johns Hopkins Hypertension (High Blood Pressure) and Stroke Glossary. Web.

Joint Commission. 2005. ACE-inhibitor and ARB contraindication/ intolerance. Web.

Medicine Net. 2005. ARB’s & ACE Inhibitors offer hidden benefits…beyond blood pressure control. Web.

Medscape Today. 2008. Therapeutic benefits of ACE inhibitors and other antihypertensive drugs in patients with Type 2 Diabetes. Web.

Sherman Health Regional Heart Centre. 2007. Glossary of cardiac terminology. Web.

The Free Dictionary. 2008. Mechanism of action. Web.

The UCB Institute of Allergy. 20008. Patients and public. Web.

Weber, C. 2008. What are Angiotensin Receptor Blockers? Web.

Your Total Health. 2008. Angiotensin II receptor blockers. Web.

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