Vasodilators in the Treatment of Hypertension

Introduction

Vasoconstriction and Vasodilation.png

Vasodilators are medicines that dilate blood vessels thus blood to flow more easily through. Some act directly on the smooth muscle cells lining the blood vessels. Other have a central effect, and regulate blood pressure most likely through the vasomotor center located within the medulla oblongata of the brain.[1]

Pharmacodynamics:

The drug class of vasodilators treat hypertension by directly vasodilating blood vessels in the periphery. Vasodilators decrease resistance in the blood vessels resulting in a decrease in blood pressure.[2] Direct-acting vasodilators dilate arterioles specifically, without having a dilating effect on the venous system.[3] Although, many antihypertensive drugs ultimately produce vasodilation through a cascade of events, this class antihypertensive drugs produce vasodilation by acting directly on the smooth muscle of the vasculature in the periphery.[4] Specifically, direct-acting vasodilators stimulate intracellular components by activating phosphorylation of cyclic-adenosine monophosphate (cAMP) and cyclic-guanosine monophosphate (cGMP).[2] These cyclic second-messengers inhibit smooth muscle contraction, as well as platelet aggregation.[2]

Pharmacokinetics and Adverse Effects:

However, direct vasodilators are usually not the first in line in the treatment of hypertension. This class of drugs have a fairly short half-life, which requires frequent doses throughout the day.[5] This class of drugs are primarily metabolized by the liver and excreted via the kidneys.[3] While vasodilators are successful in controlling hypertension, these medications possess a myriad of side effects. Reflex tachycardia is the primary adverse effect of these drugs, as a consequence of the medication induced baroreflex response compensating for the sudden medication decrease in vascular resistance. Other less serious side effects include orthostatic hypotension, dizziness, weakness, fluid retention and nausea.[6] PTs should be mindful of potential implications of adverse effects of these drugs or contraindications to therapy in patients.

See also Pharmacological Management of Hypertension

References:

  1. Drugs.com Vasodilators Available from: https://www.drugs.com/drug-class/vasodilators.html (last accessed 20.6.2019)
  2. 2.0 2.1 2.2 Walter U, Waldmann R, Nieberding M. Intracellular mechanism of action of vasodilators. European Heart Journal. 1988;9(suppl H):1-6. doi:10.1093/eurheartj/9.suppl_h.1.
  3. 3.0 3.1 Cohn JN, Mcinnes GT, Shepherd AM. Direct-Acting Vasodilators. The Journal of Clinical Hypertension. 2011;13(9):690-692.
  4. Carter B, Saseen J. Hypertension. 5th ed. New York , NY: McGraw-Hill; 2002.
  5. Patel P, Jneid H. Interventional Pharmacology-Vasodilators. The Cardiology Advisor. https://www.thecardiologyadvisor.com/cardiology/interventional-pharmacologyvasodilators/article/583886/. Published September 17, 2018. Accessed October 10, 2018.
  6. Ciccone CD. Pharmacology in Rehabilitation. 5th ed. Philadelphia: F.A. Davis Company; 2016.