C H A P T E R 3 0
Adrenergic agonists
457
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.]
Eye
Brain stem
and spinal cord
Alpha 2 receptors
modulate release
of noradrenaline
into synapse
Physiological adrenergic effects
Eyes
Pupils dilate, loss of accommodation
Mouth
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
GY
Renal blood flow
Uterine activity
Bladder relaxation
Sphincter contraction
Genital stimulation
Skin
Vasoconstriction (pale)
Piloerection
Sweating
Sympathetic
chain Nerves and
ganglia
Organs
Lacrimal gland
Parotid gland
Salivary gland
Lungs
Larynx
Heart
Stomach
Liver
Celiac
ganglion
and plexus
Superior
mesenteric
ganglion
Inferior
mesenteric
ganglion and
plexus
Pancreas
Adrenal gland
Kidney
Intestine
Colon
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.
