Nursing Pharmacology:  Autonomic Pharmacology Adrenergic Drugs

Introduction

• Distribution of adrenergic receptor subtypes and adrenergic receptor number are important factors in organ or cellular responses to adrenergic input.

  • Adrenergic receptor type in bronchiolar smooth muscle is principally ß₂: epinephrine and isoproterenol might be expected to be effective bronchodilators because of their activity at ß₂ receptors.

    • Norepinphrine is unlikely to have this same effect due to its relative lack of activity at ß₂ sites.

  • α receptor dominate in the cutaneous vascular beds.

    • Norepinephrine and epinephrine cause constriction.

    • Isoproterenol with limited activity at alpha recetors has little effect.

  • Both α and β adrenergic receptor are present in skeletal muscle vascular beds.

    • α receptor activation causes vasoconstriction.

    • β receptor activation promotes vasodilatation.

    • Since ß₂ receptors are activated at lower, physiological concentrations, vasodilation results.

• Physiological effects caused by sympathomimetcs are due not only to direct effects, but also to indirect or reflex effects.

  • α receptor agonist causes an increase in blood pressure.

  • Carotid/aortic baroreceptors activations initiates a compensatory reflex.

  • Sympathetic tone is reduced (decreases heart rate)

  • Parasympathetic tone is increased (decreases heart rate)

  • Blood pressure tends to return to lower levels

Adrenergic Agonists

--increased effect; --decreased effect

(adapted from: Table 12-1 Stoelting, R.K., "Pharmacokinetics and Pharmacodynamics of Injected and Inhaled Drugs", in Pharmacology and Physiology in Anesthetic Practice, Lippincott-Raven Publishers, 1999, p. 260)

Categories of Action

•  Smooth Muscle Effects

  • Smooth muscle activation, including activation of blood vessel vasculature (skin, kidney).

  • Activation of glands (salivary and sweat).

  • Smooth muscle inhibition, including inhibition of smooth muscle of the gut, bronchioles, and skeletal muscle vascular smooth muscle.

•  Cardiac Effects

  • Increased heart rate (positive chronotropic effect)

  • Increased contractility (positive inotropic effect)

• Metabolic Effects

  • Increase in rate of muscle and liver glycogenolysis

  • Increase in free-fatty acid release from fat

•  Endocrine

  • Regulation/modulation of insulin, pituitary, and renin secretion

•  Central Nervous System Effects

  • Respiratory stimulation

  • CNS stimulation

  • Appetite attenuation

• Presynaptic Effects

  • Presynaptic effects: modulation of  release of norepinephrine or acetylcholine

Hoffman, B.B and Lefkowitz, R.J, Catecholamines, Sympathomimetic Drugs, and Adrenergic Receptor Antagonists, In, Goodman and Gillman's The Pharmacologial Basis of Therapeutics,(Hardman, J.G, Limbird, L.E, Molinoff, P.B., Ruddon, R.W, and Gilman, A.G.,eds) TheMcGraw-Hill Companies, Inc.,1996, pp.199-242

Stoelting, R.K., "Sympathomimetics", in Pharmacology and Physiology in Anesthetic Practice, Lippincott-Raven Publishers, 1999, p. 260