Pharmacology of the ANS 3 Flashcards
Where are alpha 1 adrenoreceptors found and what do they do?
- Found in blood vessels and GI tract
- Cause vasoconstriction
Where are alpha 2 adrenoreceptors found and what do they do?
- Found in pre-synaptic cells
- Inhibit release of neurotransmitters
Where are beta 1 adrenoreceptors found and what do they do?
- Found in heart
- Increase rate and force of contraction
Where are beta 2 adrenoreceptors found and what do they do?
- Found in bronchial and uterine smooth muscle
- Cause muscle relaxation
- Also found in blood vessels in skeletal muscle
- Cause vasodilation
Describe the general effects of alpha 1 adrenoreceptors
- Activate phospholipase C to activate 2nd messengers
- Stimulation results in vasoconstriction and constriction of smooth muscle except in GI tract
What is the effect of alpha 1 stimulation on vascular smooth muscle
- Constriction
- Leads to increased peripheral resistance, decreased vascular compliance and increased central venous pressure
- Increase in systolic and diastolic arterial pressure
Describe alpha 1 adrenoreceptor antagonists and hypertension
- Selective alpha 1 adrenoreceptor antagonists such as doxazosin and prazosin cause vasodilation and fall in arterial pressure
- Used in treating resistant hypertension
- Have long plasma half-lives- can be taken once a day
- Side effects include postural hypertension and erectile dysfunction
What is the use of doxazosin as an alpha 1 adrenoreceptor antagonist?
- Relax smooth muscle in benign protastic hyperplasia, improving urinary flow
- Also evidence that these receptors play a role in trophoc response in hypertension, may prevent these changes
What is the use of alpha 1 adrenoreceptors in local anaesthetics?
- Injection of lidocaine- spreads out widely, numbness spread
- Lidocaine with adrenaline, greater focus of aneasthetic- constricted vessels in skin with adrenaline
What is the use of alpha 1 adrenoreceptors in nasal decongestants?
- Parasympathetics nervous system controls glandular secretion and causes vasodilation
- Sympathetic nervous system causes vasoconstriction
- Alpha ar agonists such as pseudophedrine and oxymetazoline will decrease nasal secretions- vasocontstriction in nose
- Parasympathetic also involved in gland regulation
What is the use of alpha 1 adrenoreceptors in other decongestants?
- Parasympathetic agents such as atropine will also reduce nasal secretions, but atropine is readily absorbed via nasal mucosa
- Can lead to many side effects but useful drug
Describe the general action of alpha 2 adrenoreceptors
- Linked to adenylate cyclase (inhibit)
- Reducing cytosolic levels of cAMP helps preventing the release of noradrenaline
Describe alpha 2 adrenoreceptor agonists and hypertension
- Selective alpha 2 AR agonists such as clonidine will inhibit the release of NA and can be used to treat resistant hypertension
- Methylnoradrenaline will also activate alpha 2 adrenoreceptors and its precursor methyl dopa (substitutes dopa in normal reaction)
- May also be used in resistant hypertension
Describe the general action of beta adrenoreceptors
- Beta receptors activate adenylate cyclase and increase cAMP levels in cell
- Beta 1 and Beta 2 differ in their distribution and their agonist/antagonist profiles
Describe the distribution of beta adrenoreceptors
- 1 in heart
- 2 in airway smooth muscle
What are the effects of beta 1 adrenoreceptor agonists?
- Increase heart rate (chonotropic) and force of contraction (inotropic)
- Reduces cardiac efficiency (amount if work required to pump blood)
- Can help restore automaticity
- Can disturb cardiac rhythm and ischaemic heart more susceptible to dysrhythmias
What are the uses and side effects of beta 1 adrenoreceptor agonist dobutamine?
- Stimulate failing heart
- Slightly more effective with inotropic than chronotropic
- High incidence of dysrhythmia
- Also reduces cardiac efficiency as oxygen consumption increases more than cardiac work
What are the effects of beta 2 adrenoreceptor agonists?
- Relax airway smooth muscle by acting directly on receptors to increase intracellular cAMP levels
- Effective regardless of constricting stimulus
- Useful in asthma where more than one bronchoconstrictor substance may be present
What are the uses of beta 2 adrenoreceptor salbutamol?
- Relieve symptoms of asthma
- Also used in COPD but are much less effective in chronic obstructive lung disease
- Agonists do not affect underlying airways inflammation inasthma and over-reliance on this form of therapy should be avoided
What are the uses of beta agonists in premature labour?
- Beta agnoists such as salbutamol relax uterine smooth muscle and can be given as an infusion to delay delivery
- Allows mother to receive steroid therapy to mature baby’s lungs
What are the effects of beta-blockers?
- Like propranolol, depend on levels of sympathetic activity
- Beta blockers have little effect on restoring heart rate, CO or arterial pressure normally but will blunt effects of exercise on these variables
- Exercise tolerance reduced because of effects on heart and loss of vasodilation in skeletal muscles
How do beta blockers reduce hypertension?
- Reduce cardiac output
- Reduce sympathetic activity
- Modify renin (kidney hormone that is involved in blood pressure) release
Why is hypertension bad?
- May lead to heart attacks or strokes
What are the uses of beta 1 adrenoreceptor antagonists?
- While receptor agonists are used to stimulate failing heart, antagnists also used to treat angina pectoris
- Work by improving oxygenation of heart muscle
- Also used to regulate dysrhythmias
