Cardio: Adrenergic Drugs Flashcards
- Affects:
- α1, α2
- β1
Norepinephrine
- Affects:
- α1, α2
- β1, β2, β3
Epinephrine
- Affects:
- β1, β2, β3
- D1 (& D5), D2 (& D3, D4)
- At high concentrations: α1
Dopamine
Adrenergic receptors of the
Heart
- β1 = Increased contractility
- β1 = Increased automaticity
- β1 = Increased conduction velocity
Adrenergic receptors fo the
Blood Vessels
- α1 = Arteriolar constriction
- β2 = Arteriolar dilation of Skeletal muscle and Liver
- D1 = Arteriolar dilation of Kidney and Mesentry
- α1 = Venoconstriction
- β2 = Venodilation
Adrenergic receptors of the
Bronchioles
- β2 = Bronchodilation
Adrenergic receptors of the
Iris
- α1 = Radial muscle contraction –> mydriasis
Adrenergic receptors of the
GI Tract and Urinary Bladder
- α1 = Sphincter contraction
- β2 = Decreased motility
Adrenergic receptors of the
Uterus
- β1 = Relaxation of uterus
Metabolic affects of adrenergic receptors on the
Liver
- α1 / β2 = Gluconeogenesis, Glycogenolysis
Metabolic affects of adrenergic receptors on the
Fat
- β1 / β3 = Lipolysis
Metabolic affects of adrenergic receptors on the
Pancreas
- α2 = Decreased insulin secretion
Metabolic affects of adrenergic receptors on the
Kidney
- β1 = Renin secretion
- These receptors include typical postsynaptic receptors mediating smooth-muscle contraction
α1
- These receptors include presynaptic autoregulatory and postsynaptic receptors
- Activation of prysynaptic autoregulatory inhibits NE release while blockage of the presynaptic receptors enhances NE releaase
- Postsynaptic receptors exist in extrasynaptic vascular smooth muscle, ciliary, epithelium, and in the brain
α2
Mechanism of Transduction
β1
- Gs protein
- Increases adenylyl cyclase activity
- Opens L-type Ca2+ channels
Mechanism of Transduction
β2
- Gs protein
- Increases adenylyl cyclase activity
Mechanism of Transduction
β3
- Gs protein
- Increases adenylyl cyclase activity
Mechanism of Transduction
α1
- Gq protein
- Increases phospholipase C –> *Increases *IP3
- -> Increases Ca2+
- *Increases *phospholipase D (Minor effectors)
- Gq, Gi/Go
- Increases phospholipase A2 (Minor effectors)
Mechanism of Transduction
α2
- Gi protein
- decreases adenylyl cyclase activity
- Gi (via βy subunits)
- Opens K+ channels (L- and N- types)
- Go
- Closes Ca2+ channels
Epinephrine cardiac effects
- β1 actions
- Increases automaticity, Heart Rate, Conduction velocity, Myocardial contractile force (MCF), Cardiac output (CO), and O2 consumption
- Accelerates phase 4 diastolic depolarization in Purkinje fibers and further facilitates activation of latent pacemaker cells
- Can cause ventricular arrhythmias (especially in the presence of halogenated hydrocarbon anesthetics)
Epinephrine vascular effects on
peripheral resistance and blood pressure
- Increases Cutaneous, Mesenteric, and Renal vascular resistance (α1 receptor)
- Decreases Skeletal and Liver vascular resistance at low concentrations (β2 receptor > α1 receptor) –> dilation
- Increases Skeletal and Liver vascular resistance at high concentrations (α1 receptor > β2 receptor) –> constriction
- Low Dose Epi - decrease BP (β2) vasodilation, *increase HR (β1), **decrease* or no change in Mean Blood Pressure (MBP)
- High Dose Epi - Increase MBP (α1) both Sys / Dia
Epinephrine nonvascular effects on
Bronchiole Smooth Muscle
- Relaxes Bronchal smooth muscle (β2)
- Most evident when bronchial muscle is contracted due to disease or drugs
Epinephrine Metabolic effects
- Hyperglycemia occurs due to gluconeogenesis and glycogenolysis in the Liver (α1 / β2)
- Inhibition of insulin release (α2) from Pancreas
- Lipolysis elevates free Fatty Acids in the blood (β1 and β3)
Norepinephrine effects the
Blood pressure and Vasculature
- Increases peripheral resistance in most vascular beds (α1) with no dilation anywhere
- Increases Total peripheral resistance (TRP)
- Increases Mean Blood Pressure (MBP)
- Decreases Blood flow in the Skin, Kidney, Liver, and Skeletal muscle w/ flow to CNS not reduced
Norepinephrine cardiac effects
- β1 actions same as Epinephrine
- Heart rate decreases due to compensatory Vagal reflex activity initiated by the elevated MBP; overcomes the direct cardioacceleratory action of β1 receptor activation
α receptor general locations
- α1 - post-synaptic
- α2 - pre and post-synaptic (β cells of the Pancreas)
β receptor general locations
- β1 - post-synaptic
- β2 - extra-junctional on EO (end organs)
- NEVER at synaptic nerve terminal
- β3 -
D receptor general locations
- D1 - post-synaptic
- D2 - pre and post-synaptic
