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C H A P T E R 3 0 Adrenergic agonists

of the heart muscle. b 2 -receptors on the other hand are found in the lung, the uterus and the liver. A very impor- tant function of b 2 -receptors is to cause opening of the airways by dilation of bronchial muscle. Stimulation of b 2 -receptors also results in glycogenolysis and relaxation of the uterus. Therapeutic actions and indications The effects of the sympathomimetic drugs are mediated by the adrenergic receptors in target organs: heart rate increases with increased myocardial contractility; bron- chioles dilate and respirations increase in rate and depth; blood vessels constrict, causing an increase in blood pressure; intraocular pressure decreases; glycogenoly- sis (breakdown of glucose stores so that the glucose can be used as energy) occurs; pupils dilate; and sweating can increase (see Figure 30.2). These drugs are gener- ally indicated for the treatment of hypotensive states or shock, bronchospasm and some types of asthma.

FIGURE 30.1  After gently exposing the lower conjunctival sac, an eyedrop is administered. [From Lynn, P. (2006). Taylor’s clinical nursing skills: A nursing process approach (2nd edn). Philadelphia: Lippincott Williams & Wilkins, p. 244, Figure 4.]

Brain stem and spinal cord Alpha 2 receptors

Sympathetic chain Nerves and ganglia

Physiological adrenergic effects Eyes Pupils dilate, loss of accommodation Mouth

modulate release of noradrenaline into synapse

Organs

Eye

Salivation Secretions Respiratory tract Bronchodilation R depth of respirations CV P + Inotrope effect Conduction Vasoconstriction, BP blood flow to muscles GI Pancreatic secretions Gastric secretions GI motility Perfusion Sphincter contraction Renal blood flow Uterine activity Bladder relaxation Sphincter contraction Genital stimulation Skin Vasoconstriction (pale) Piloerection Sweating GY

Lacrimal gland Parotid gland Salivary gland

Lungs Larynx

Heart

Stomach

Liver

Celiac ganglion and plexus

Pancreas Adrenal gland Kidney Intestine Colon

Superior mesenteric ganglion

Inferior mesenteric ganglion and plexus

Bladder

Reproductive organs

FIGURE 30.2  Sympathetic nervous system and physiological effects of adrenergic stimulation. Adrenergic agonists cause stimulation of adrenergic receptors, producing physiological effects associated with sympathetic stimulation. Receptor-site-specific adrenergic agonists have more pronounced effect on particular responses.