Sympathomimetics Flashcards
What are alpha and beta agonists?
Alpha agonists and beta agonists are two types of adrenergic medications that stimulate their respective receptors and mimic the effect of endogenous catecholamines, like norepinephrine and epinephrine.
Where are alpha 1 receptors located and what do they do?
Alpha-1 adrenergic receptors are mainly located on the walls of blood vessels, and when stimulated, they cause vasoconstriction, thus decreasing blood flow to tissues.
In the eyes, alpha-1 adrenergic receptors also trigger mydriasis, or pupil dilation.
In the bladder, they cause sphincter constriction and urinary retention, or holding the urine within the bladder.
And in males, they trigger ejaculation
Where are alpha 2 receptors located and what do they do?
Alpha-2 adrenergic receptors are primarily found on the presynaptic neuron. So when a presynaptic nerve ending is stimulated to release noradrenaline in the synaptic cleft, some of that norepinephrine binds to alpha-2 receptors on the presynaptic membrane. This inhibits further release of norepinephrine and serves as a mechanism of negative feedback control.
Where are Beta 1 receptors found and what do they do?
Beta-1 adrenergic receptors are mainly located in the heart, where they increase the heart rate and contractility, which helps pump out more blood.
Beta-1 receptors are also found in the kidney, where they stimulate a very special kind of cell, called juxtaglomerular cells, to release renin.
Where are beta 2 receptors found and what do they do?
Beta 2 receptors are found on smooth muscle cells in the walls of blood vessels supplying skeletal muscles and the brain, leading to vasodilation and increased blood flow to these tissues.
In the lungs, beta-2 adrenergic receptors cause bronchodilation, increasing oxygen delivery to cells.
In the gastrointestinal tract, they decrease motility and slow digestion.
In the eyes, they act on the ciliary body to promote the secretion of aqueous humor, which provides support and helps to maintain the shape of the eye.
In the liver, they cause more glucose to be released into the blood; and in the pancreatic islets of Langerhans, they promote the release of glucagon, which again, helps raise blood glucose levels.
Finally, They stimulate an enzyme found on the surface of the cells lining capillary walls called lipoprotein lipase, which breaks down triglycerides into free fatty acids and cholesterol.
How many types of sympathomimetics are there?
Three types
direct-acting agonists, which directly activate adrenergic receptors to produce the desired effect;
indirect-acting agonists like amphetamines and cocaine, which increase the release of endogenous catecholamines and enhance their effect;
mixed-acting agonists like ephedrine, which utilize both of these mechanisms.
What does phenylephrine do?
phenylephrine causes systemic vasoconstriction and increases blood pressure, therefore it’s used to treat hypotension.
But, when blood pressure increases, the body compensates by lowering the heart rate, leading to compensatory bradycardia, which is a slower than normal heart rate.
