Morgan & Mikhail Chap 14(Adrenergic Agonists & Antagonists)

Question 1

ADRENOCEPTOR PHYSIOLOGY

Answer 1

The term adrenergic originally referred to the effects of epinephrine (adrenaline), though norepinephrine (noradrenaline) is the primary neurotransmitter responsible for most of the adrenergic activity of the sympathetic nervous system. With the exception of eccrine sweat glands and some blood vessels, norepinephrine is released by postganglionic sympathetic fibers at end-organ tissues (Figure 14–1). In contrast, acetylcholine is released by preganglionic sympathetic fibers and all parasympathetic fibers.

Question 2

α1-Receptors

Answer 2

Question 3

α2-Receptors

Answer 3

Question 4

β1-Receptors

Answer 4

Question 5

β2-Receptors

Answer 5

Question 6

β3-Receptors

Answer 6

β3-Receptors are found in the gallbladder and brain adipose tissue. Their role in
gallbladder physiology is unknown, but they are thought to play a role in lipolysis, thermogenesis in brown fat, and bladder relaxation.

Question 7

Dopaminergic Receptors

Answer 7

Dopamine (DA) receptors are a group of adrenergic receptors that are activated by dopamine; these receptors are classified as D1 and D2 receptors. Activation of D1 receptors mediates vasodilation in the kidney, intestine, and heart. D2 receptors are believed to play a role in the antiemetic action of droperidol, haloperidol, and related agents

Question 8

Adrenergic Agonists

Answer 8

Adrenergic agonists interact with varying specificity (selectivity) at α- and β-
adrenoceptors

“Overlapping” receptor activity complicates the prediction of clinical effects.
For example, epinephrine stimulates α1-, α2-, β1-, and β2-adrenoceptors. Its net effect on arterial blood pressure depends on the dose-dependent balance between α1 vasoconstriction, α2- and β2-vasodilation, and β1-inotropic influences (and, to a minor degree, β2-inotropic influences).

Question 9

Receptor selectivity of adrenergic agonists

Answer 9

Question 10

Effects of adrenergic agonists on organ systems

Answer 10

Question 11

Adrenergic agonists can be categorized as direct or indirect

Answer 11

Direct agonists bind to the
receptor, whereas indirect agonists increase endogenous neurotransmitter activity.

Question 12

PHENYLEPHRINE

Answer 12

Question 13

α2-AGONISTS

Answer 13

Clonidine decreases anesthetic and analgesic requirements (decreases minimum alveolar concentration) and provides sedation and anxiolysis

Dexmedetomidine has
sedative, analgesic, and sympatholytic effects that blunt many of the cardiovascular responses seen during the perioperative period.

Question 14

EPINEPHRINE

Answer 14

Question 15

EPHEDRINE

Answer 15

Question 16

NOREPINEPHRINE

Answer 16

Question 17

DOPAMINE

Answer 17

Question 18

DOBUTAMINE

Answer 18

Question 19

Adrenergic Antagonists

Answer 19

Adrenergic antagonists bind but do not activate adrenoceptors. They prevent adrenergic
agonist activity. Like the agonists, the antagonists differ in their spectrum of receptor interaction

Question 20

MIXED ANTAGONISTS: LABETALOL

Answer 20

Labetalol lowers blood pressure without reflex tachycardia because of its combination of α and β effects, which is beneficial to patients with coronary artery disease

Question 21

β-BLOCKERS

Answer 21

β-Receptor blockers have variable degrees of selectivity for the β1-receptors. Those that are more β1 selective have less influence on bronchopulmonary and vascular β2- receptors (Table 14–3). Theoretically, a selective β1-blocker would have less of an inhibitory effect on β2-receptors and, therefore, might be preferred in patients with
chronic obstructive lung disease or peripheral vascular disease. Patients with peripheral vascular disease could potentially have a decrease in blood flow if β2- receptors, which dilate the arterioles, are blocked. β-Receptor blocking agents also reduce intraocular pressure in patients with glaucoma.

Question 22

ESMOLOL

Answer 22

Esmolol is an ultrashort-acting selective β1-antagonist that reduces heart rate and,
to a lesser extent, blood pressure.

Question 23

METOPROLOL

Answer 23

Metoprolol is a selective β1-antagonist with no intrinsic sympathomimetic activity. It is available for both oral and intravenous use. It can be administered intravenously in 1 to 5 mg increments every 2 to 5 min, titrated to blood pressure and heart rate. Extended release
metoprolol given orally can be used to treat patients with chronic heart failure.

Question 24

PERIOPERATIVE β-BLOCKER THERAPY

Answer 24

Abrupt discontinuation of β-blocker therapy for 24 to 48 h may trigger a withdrawal syndrome characterized by rebound hypertension, tachycardia, and angina
pectoris. This effect seems to be caused by an increase in the number of β-adrenergic receptors (upregulation).

Question 25

Pharmacology of β-blockers

Answer 25