How a beta receptor antagonist causes a decrease in blood pressure?
To understand how beta adrenergic blockade lowers blood
pressure, you need to understand a little physiology.
Beta receptors are present in many different places in the body:
the heart, the blood vessels, the kidneys, the lungs, the muscles,
etc. They perform different tasks in each different place as well,
and there are different classes of receptors. For instance, in the
heart, the receptors are called beta-1 receptors and they increase
the rate of firing of the SA node (chronotropy), increases cardiac
conduction velocity (dromotropy) and increase the strength with
which the heart beats (inotropy). In the arterioles, the receptors
cause dilatation of the vessels and are called beta-2 receptors. In
the kidneys, beta-1 receptors increase renin output from the
juxtamedullary cells when stimulated. Renin is an enzyme that
produces a potent vasocontrictor when it activates the angiotensin
cascade.
Now, how does beta antagonism lower blood pressure. First, in
the heart, beta blockade causes a slowing of the heart rate and
stroke volume, effectively decreasing cardiac output. In the
kidneys, beta blockade decreases renin release, which decreases the
amount of systemic vasoconstrictors in the body. These two effects
cause the blood pressure to decrease over time.
